Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1 ACPI ACPI support is enabled.
2 AGP AGP (Accelerated Graphics Port) is enabled.
3 ALSA ALSA sound support is enabled.
4 APIC APIC support is enabled.
5 APM Advanced Power Management support is enabled.
6 APPARMOR AppArmor support is enabled.
7 ARM ARM architecture is enabled.
8 ARM64 ARM64 architecture is enabled.
9 CLK Common clock infrastructure is enabled.
10 CMA Contiguous Memory Area support is enabled.
11 DRM Direct Rendering Management support is enabled.
12 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
13 EARLY Parameter processed too early to be embedded in initrd.
14 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
15 EFI EFI Partitioning (GPT) is enabled
16 EVM Extended Verification Module
17 FB The frame buffer device is enabled.
18 FTRACE Function tracing enabled.
19 GCOV GCOV profiling is enabled.
20 HIBERNATION HIBERNATION is enabled.
21 HW Appropriate hardware is enabled.
22 HYPER_V HYPERV support is enabled.
23 IMA Integrity measurement architecture is enabled.
24 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
25 IPV6 IPv6 support is enabled.
26 ISAPNP ISA PnP code is enabled.
27 ISDN Appropriate ISDN support is enabled.
28 ISOL CPU Isolation is enabled.
29 JOY Appropriate joystick support is enabled.
30 KGDB Kernel debugger support is enabled.
31 KVM Kernel Virtual Machine support is enabled.
32 LIBATA Libata driver is enabled
33 LOONGARCH LoongArch architecture is enabled.
34 LOOP Loopback device support is enabled.
35 LP Printer support is enabled.
36 M68k M68k architecture is enabled.
37 These options have more detailed description inside of
38 Documentation/arch/m68k/kernel-options.rst.
39 MDA MDA console support is enabled.
40 MIPS MIPS architecture is enabled.
41 MOUSE Appropriate mouse support is enabled.
42 MSI Message Signaled Interrupts (PCI).
43 MTD MTD (Memory Technology Device) support is enabled.
44 NET Appropriate network support is enabled.
45 NFS Appropriate NFS support is enabled.
46 NUMA NUMA support is enabled.
47 OF Devicetree is enabled.
48 PARISC The PA-RISC architecture is enabled.
49 PCI PCI bus support is enabled.
50 PCIE PCI Express support is enabled.
51 PCMCIA The PCMCIA subsystem is enabled.
52 PNP Plug & Play support is enabled.
53 PPC PowerPC architecture is enabled.
54 PPT Parallel port support is enabled.
55 PS2 Appropriate PS/2 support is enabled.
56 PV_OPS A paravirtualized kernel is enabled.
57 RAM RAM disk support is enabled.
58 RDT Intel Resource Director Technology.
59 RISCV RISCV architecture is enabled.
60 S390 S390 architecture is enabled.
61 SCSI Appropriate SCSI support is enabled.
62 A lot of drivers have their options described inside
63 the Documentation/scsi/ sub-directory.
64 SDW SoundWire support is enabled.
65 SECURITY Different security models are enabled.
66 SELINUX SELinux support is enabled.
67 SERIAL Serial support is enabled.
68 SH SuperH architecture is enabled.
69 SMP The kernel is an SMP kernel.
70 SPARC Sparc architecture is enabled.
71 SUSPEND System suspend states are enabled.
72 SWSUSP Software suspend (hibernation) is enabled.
73 TPM TPM drivers are enabled.
74 UMS USB Mass Storage support is enabled.
75 USB USB support is enabled.
76 NVME NVMe support is enabled
77 USBHID USB Human Interface Device support is enabled.
78 V4L Video For Linux support is enabled.
79 VGA The VGA console has been enabled.
80 VMMIO Driver for memory mapped virtio devices is enabled.
81 VT Virtual terminal support is enabled.
82 WDT Watchdog support is enabled.
83 X86-32 X86-32, aka i386 architecture is enabled.
84 X86-64 X86-64 architecture is enabled.
85 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
86 X86_UV SGI UV support is enabled.
87 XEN Xen support is enabled
88 XTENSA xtensa architecture is enabled.
89
90In addition, the following text indicates that the option
91
92 BOOT Is a boot loader parameter.
93 BUGS= Relates to possible processor bugs on the said processor.
94 KNL Is a kernel start-up parameter.
95
96
97Kernel parameters
98
99 accept_memory= [MM]
100 Format: { eager | lazy }
101 default: lazy
102 By default, unaccepted memory is accepted lazily to
103 avoid prolonged boot times. The lazy option will add
104 some runtime overhead until all memory is eventually
105 accepted. In most cases the overhead is negligible.
106 For some workloads or for debugging purposes
107 accept_memory=eager can be used to accept all memory
108 at once during boot.
109
110 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY]
111 Advanced Configuration and Power Interface
112 Format: { force | on | off | strict | noirq | rsdt |
113 copy_dsdt | nospcr }
114 force -- enable ACPI if default was off
115 on -- enable ACPI but allow fallback to DT [arm64,riscv64]
116 off -- disable ACPI if default was on
117 noirq -- do not use ACPI for IRQ routing
118 strict -- Be less tolerant of platforms that are not
119 strictly ACPI specification compliant.
120 rsdt -- prefer RSDT over (default) XSDT
121 copy_dsdt -- copy DSDT to memory
122 nocmcff -- Disable firmware first mode for corrected
123 errors. This disables parsing the HEST CMC error
124 source to check if firmware has set the FF flag. This
125 may result in duplicate corrected error reports.
126 nospcr -- disable console in ACPI SPCR table as
127 default _serial_ console on ARM64
128 spcr -- enable console in ACPI SPCR table as
129 default _serial_ console on x86
130 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or
131 "acpi=nospcr" are available
132 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force"
133 are available
134
135 See also Documentation/power/runtime_pm.rst, pci=noacpi
136
137 acpi_apic_instance= [ACPI,IOAPIC,EARLY]
138 Format: <int>
139 2: use 2nd APIC table, if available
140 1,0: use 1st APIC table
141 default: 0
142
143 acpi_backlight= [HW,ACPI]
144 { vendor | video | native | none }
145 If set to vendor, prefer vendor-specific driver
146 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
147 of the ACPI video.ko driver.
148 If set to video, use the ACPI video.ko driver.
149 If set to native, use the device's native backlight mode.
150 If set to none, disable the ACPI backlight interface.
151
152 acpi_force_32bit_fadt_addr [ACPI,EARLY]
153 force FADT to use 32 bit addresses rather than the
154 64 bit X_* addresses. Some firmware have broken 64
155 bit addresses for force ACPI ignore these and use
156 the older legacy 32 bit addresses.
157
158 acpica_no_return_repair [HW, ACPI]
159 Disable AML predefined validation mechanism
160 This mechanism can repair the evaluation result to make
161 the return objects more ACPI specification compliant.
162 This option is useful for developers to identify the
163 root cause of an AML interpreter issue when the issue
164 has something to do with the repair mechanism.
165
166 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
167 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
168 Format: <int>
169 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
170 debug output. Bits in debug_layer correspond to a
171 _COMPONENT in an ACPI source file, e.g.,
172 #define _COMPONENT ACPI_EVENTS
173 Bits in debug_level correspond to a level in
174 ACPI_DEBUG_PRINT statements, e.g.,
175 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
176 The debug_level mask defaults to "info". See
177 Documentation/firmware-guide/acpi/debug.rst for more information about
178 debug layers and levels.
179
180 Enable processor driver info messages:
181 acpi.debug_layer=0x20000000
182 Enable AML "Debug" output, i.e., stores to the Debug
183 object while interpreting AML:
184 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
185 Enable all messages related to ACPI hardware:
186 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
187
188 Some values produce so much output that the system is
189 unusable. The "log_buf_len" parameter may be useful
190 if you need to capture more output.
191
192 acpi.poweroff_on_fatal= [ACPI]
193 {0 | 1}
194 Causes the system to poweroff when the ACPI bytecode signals
195 a fatal error. The default value of this setting is 1.
196 Overriding this value should only be done for diagnosing
197 ACPI firmware problems, as the system might behave erratically
198 after having encountered a fatal ACPI error.
199
200 acpi_enforce_resources= [ACPI]
201 { strict | lax | no }
202 Check for resource conflicts between native drivers
203 and ACPI OperationRegions (SystemIO and SystemMemory
204 only). IO ports and memory declared in ACPI might be
205 used by the ACPI subsystem in arbitrary AML code and
206 can interfere with legacy drivers.
207 strict (default): access to resources claimed by ACPI
208 is denied; legacy drivers trying to access reserved
209 resources will fail to bind to device using them.
210 lax: access to resources claimed by ACPI is allowed;
211 legacy drivers trying to access reserved resources
212 will bind successfully but a warning message is logged.
213 no: ACPI OperationRegions are not marked as reserved,
214 no further checks are performed.
215
216 acpi_force_table_verification [HW,ACPI,EARLY]
217 Enable table checksum verification during early stage.
218 By default, this is disabled due to x86 early mapping
219 size limitation.
220
221 acpi_irq_balance [HW,ACPI]
222 ACPI will balance active IRQs
223 default in APIC mode
224
225 acpi_irq_nobalance [HW,ACPI]
226 ACPI will not move active IRQs (default)
227 default in PIC mode
228
229 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
230 Format: <irq>,<irq>...
231
232 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
233 use by PCI
234 Format: <irq>,<irq>...
235
236 acpi_mask_gpe= [HW,ACPI]
237 Due to the existence of _Lxx/_Exx, some GPEs triggered
238 by unsupported hardware/firmware features can result in
239 GPE floodings that cannot be automatically disabled by
240 the GPE dispatcher.
241 This facility can be used to prevent such uncontrolled
242 GPE floodings.
243 Format: <byte> or <bitmap-list>
244
245 acpi_no_auto_serialize [HW,ACPI]
246 Disable auto-serialization of AML methods
247 AML control methods that contain the opcodes to create
248 named objects will be marked as "Serialized" by the
249 auto-serialization feature.
250 This feature is enabled by default.
251 This option allows to turn off the feature.
252
253 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
254 kernels.
255
256 acpi_no_static_ssdt [HW,ACPI,EARLY]
257 Disable installation of static SSDTs at early boot time
258 By default, SSDTs contained in the RSDT/XSDT will be
259 installed automatically and they will appear under
260 /sys/firmware/acpi/tables.
261 This option turns off this feature.
262 Note that specifying this option does not affect
263 dynamic table installation which will install SSDT
264 tables to /sys/firmware/acpi/tables/dynamic.
265
266 acpi_no_watchdog [HW,ACPI,WDT]
267 Ignore the ACPI-based watchdog interface (WDAT) and let
268 a native driver control the watchdog device instead.
269
270 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY]
271 Pass the RSDP address to the kernel, mostly used
272 on machines running EFI runtime service to boot the
273 second kernel for kdump.
274
275 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
276 Format: To spoof as Windows 98: ="Microsoft Windows"
277
278 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
279 of 2 which is mandated by ACPI 6) as the supported ACPI
280 specification revision (when using this switch, it may
281 be necessary to carry out a cold reboot _twice_ in a
282 row to make it take effect on the platform firmware).
283
284 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
285 acpi_osi="string1" # add string1
286 acpi_osi="!string2" # remove string2
287 acpi_osi=!* # remove all strings
288 acpi_osi=! # disable all built-in OS vendor
289 strings
290 acpi_osi=!! # enable all built-in OS vendor
291 strings
292 acpi_osi= # disable all strings
293
294 'acpi_osi=!' can be used in combination with single or
295 multiple 'acpi_osi="string1"' to support specific OS
296 vendor string(s). Note that such command can only
297 affect the default state of the OS vendor strings, thus
298 it cannot affect the default state of the feature group
299 strings and the current state of the OS vendor strings,
300 specifying it multiple times through kernel command line
301 is meaningless. This command is useful when one do not
302 care about the state of the feature group strings which
303 should be controlled by the OSPM.
304 Examples:
305 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
306 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
307 can make '_OSI("Windows 2000")' TRUE.
308
309 'acpi_osi=' cannot be used in combination with other
310 'acpi_osi=' command lines, the _OSI method will not
311 exist in the ACPI namespace. NOTE that such command can
312 only affect the _OSI support state, thus specifying it
313 multiple times through kernel command line is also
314 meaningless.
315 Examples:
316 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
317 FALSE.
318
319 'acpi_osi=!*' can be used in combination with single or
320 multiple 'acpi_osi="string1"' to support specific
321 string(s). Note that such command can affect the
322 current state of both the OS vendor strings and the
323 feature group strings, thus specifying it multiple times
324 through kernel command line is meaningful. But it may
325 still not able to affect the final state of a string if
326 there are quirks related to this string. This command
327 is useful when one want to control the state of the
328 feature group strings to debug BIOS issues related to
329 the OSPM features.
330 Examples:
331 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
332 '_OSI("Module Device")' FALSE.
333 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
334 '_OSI("Module Device")' TRUE.
335 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
336 equivalent to
337 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
338 and
339 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
340 they all will make '_OSI("Windows 2000")' TRUE.
341
342 acpi_pm_good [X86]
343 Override the pmtimer bug detection: force the kernel
344 to assume that this machine's pmtimer latches its value
345 and always returns good values.
346
347 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode
348 Format: { level | edge | high | low }
349
350 acpi_skip_timer_override [HW,ACPI,EARLY]
351 Recognize and ignore IRQ0/pin2 Interrupt Override.
352 For broken nForce2 BIOS resulting in XT-PIC timer.
353
354 acpi_sleep= [HW,ACPI] Sleep options
355 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig,
356 s4_nohwsig, old_ordering, nonvs,
357 sci_force_enable, nobl }
358 See Documentation/power/video.rst for information on
359 s3_bios and s3_mode.
360 s3_beep is for debugging; it makes the PC's speaker beep
361 as soon as the kernel's real-mode entry point is called.
362 s4_hwsig causes the kernel to check the ACPI hardware
363 signature during resume from hibernation, and gracefully
364 refuse to resume if it has changed. This complies with
365 the ACPI specification but not with reality, since
366 Windows does not do this and many laptops do change it
367 on docking. So the default behaviour is to allow resume
368 and simply warn when the signature changes, unless the
369 s4_hwsig option is enabled.
370 s4_nohwsig prevents ACPI hardware signature from being
371 used (or even warned about) during resume.
372 old_ordering causes the ACPI 1.0 ordering of the _PTS
373 control method, with respect to putting devices into
374 low power states, to be enforced (the ACPI 2.0 ordering
375 of _PTS is used by default).
376 nonvs prevents the kernel from saving/restoring the
377 ACPI NVS memory during suspend/hibernation and resume.
378 sci_force_enable causes the kernel to set SCI_EN directly
379 on resume from S1/S3 (which is against the ACPI spec,
380 but some broken systems don't work without it).
381 nobl causes the internal blacklist of systems known to
382 behave incorrectly in some ways with respect to system
383 suspend and resume to be ignored (use wisely).
384
385 acpi_use_timer_override [HW,ACPI,EARLY]
386 Use timer override. For some broken Nvidia NF5 boards
387 that require a timer override, but don't have HPET
388
389 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in
390 kernel's map of available physical RAM.
391
392 agp= [AGP]
393 { off | try_unsupported }
394 off: disable AGP support
395 try_unsupported: try to drive unsupported chipsets
396 (may crash computer or cause data corruption)
397
398 ALSA [HW,ALSA]
399 See Documentation/sound/alsa-configuration.rst
400
401 alignment= [KNL,ARM]
402 Allow the default userspace alignment fault handler
403 behaviour to be specified. Bit 0 enables warnings,
404 bit 1 enables fixups, and bit 2 sends a segfault.
405
406 align_va_addr= [X86-64]
407 Align virtual addresses by clearing slice [14:12] when
408 allocating a VMA at process creation time. This option
409 gives you up to 3% performance improvement on AMD F15h
410 machines (where it is enabled by default) for a
411 CPU-intensive style benchmark, and it can vary highly in
412 a microbenchmark depending on workload and compiler.
413
414 32: only for 32-bit processes
415 64: only for 64-bit processes
416 on: enable for both 32- and 64-bit processes
417 off: disable for both 32- and 64-bit processes
418
419 alloc_snapshot [FTRACE]
420 Allocate the ftrace snapshot buffer on boot up when the
421 main buffer is allocated. This is handy if debugging
422 and you need to use tracing_snapshot() on boot up, and
423 do not want to use tracing_snapshot_alloc() as it needs
424 to be done where GFP_KERNEL allocations are allowed.
425
426 allow_mismatched_32bit_el0 [ARM64,EARLY]
427 Allow execve() of 32-bit applications and setting of the
428 PER_LINUX32 personality on systems where only a strict
429 subset of the CPUs support 32-bit EL0. When this
430 parameter is present, the set of CPUs supporting 32-bit
431 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
432 and hot-unplug operations may be restricted.
433
434 See Documentation/arch/arm64/asymmetric-32bit.rst for more
435 information.
436
437 amd_iommu= [HW,X86-64]
438 Pass parameters to the AMD IOMMU driver in the system.
439 Possible values are:
440 fullflush - Deprecated, equivalent to iommu.strict=1
441 off - do not initialize any AMD IOMMU found in
442 the system
443 force_isolation - Force device isolation for all
444 devices. The IOMMU driver is not
445 allowed anymore to lift isolation
446 requirements as needed. This option
447 does not override iommu=pt
448 force_enable - Force enable the IOMMU on platforms known
449 to be buggy with IOMMU enabled. Use this
450 option with care.
451 pgtbl_v1 - Use v1 page table for DMA-API (Default).
452 pgtbl_v2 - Use v2 page table for DMA-API.
453 irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
454 nohugepages - Limit page-sizes used for v1 page-tables
455 to 4 KiB.
456 v2_pgsizes_only - Limit page-sizes used for v1 page-tables
457 to 4KiB/2Mib/1GiB.
458
459
460 amd_iommu_dump= [HW,X86-64]
461 Enable AMD IOMMU driver option to dump the ACPI table
462 for AMD IOMMU. With this option enabled, AMD IOMMU
463 driver will print ACPI tables for AMD IOMMU during
464 IOMMU initialization.
465
466 amd_iommu_intr= [HW,X86-64]
467 Specifies one of the following AMD IOMMU interrupt
468 remapping modes:
469 legacy - Use legacy interrupt remapping mode.
470 vapic - Use virtual APIC mode, which allows IOMMU
471 to inject interrupts directly into guest.
472 This mode requires kvm-amd.avic=1.
473 (Default when IOMMU HW support is present.)
474
475 amd_pstate= [X86,EARLY]
476 disable
477 Do not enable amd_pstate as the default
478 scaling driver for the supported processors
479 passive
480 Use amd_pstate with passive mode as a scaling driver.
481 In this mode autonomous selection is disabled.
482 Driver requests a desired performance level and platform
483 tries to match the same performance level if it is
484 satisfied by guaranteed performance level.
485 active
486 Use amd_pstate_epp driver instance as the scaling driver,
487 driver provides a hint to the hardware if software wants
488 to bias toward performance (0x0) or energy efficiency (0xff)
489 to the CPPC firmware. then CPPC power algorithm will
490 calculate the runtime workload and adjust the realtime cores
491 frequency.
492 guided
493 Activate guided autonomous mode. Driver requests minimum and
494 maximum performance level and the platform autonomously
495 selects a performance level in this range and appropriate
496 to the current workload.
497
498 amd_prefcore=
499 [X86]
500 disable
501 Disable amd-pstate preferred core.
502
503 amd_dynamic_epp=
504 [X86]
505 disable
506 Disable amd-pstate dynamic EPP.
507 enable
508 Enable amd-pstate dynamic EPP.
509
510 amijoy.map= [HW,JOY] Amiga joystick support
511 Map of devices attached to JOY0DAT and JOY1DAT
512 Format: <a>,<b>
513 See also Documentation/input/joydev/joystick.rst
514
515 analog.map= [HW,JOY] Analog joystick and gamepad support
516 Specifies type or capabilities of an analog joystick
517 connected to one of 16 gameports
518 Format: <type1>,<type2>,..<type16>
519
520 apc= [HW,SPARC]
521 Power management functions (SPARCstation-4/5 + deriv.)
522 Format: noidle
523 Disable APC CPU standby support. SPARCstation-Fox does
524 not play well with APC CPU idle - disable it if you have
525 APC and your system crashes randomly.
526
527 apic [APIC,X86-64] Use IO-APIC. Default.
528
529 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller
530 Change the output verbosity while booting
531 Format: { quiet (default) | verbose | debug }
532 Change the amount of debugging information output
533 when initialising the APIC and IO-APIC components.
534
535 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting
536 Format: { bsp (default) | all | none }
537 bsp: External NMI is delivered only to CPU 0
538 all: External NMIs are broadcast to all CPUs as a
539 backup of CPU 0
540 none: External NMI is masked for all CPUs. This is
541 useful so that a dump capture kernel won't be
542 shot down by NMI
543
544 apicpmtimer Do APIC timer calibration using the pmtimer. Implies
545 apicmaintimer. Useful when your PIT timer is totally
546 broken.
547
548 autoconf= [IPV6]
549 See Documentation/networking/ipv6.rst.
550
551 apm= [APM] Advanced Power Management
552 See header of arch/x86/kernel/apm_32.c.
553
554 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
555 Format: { "0" | "1" }
556 See security/apparmor/Kconfig help text
557 0 -- disable.
558 1 -- enable.
559 Default value is set via kernel config option.
560
561 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
562 Format: <io>,<irq>,<nodeID>
563
564 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of
565 32 bit applications.
566
567 arm64.nobti [ARM64] Unconditionally disable Branch Target
568 Identification support
569
570 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack
571 support
572
573 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
574 Set instructions support
575
576 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And
577 Monitoring support
578
579 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
580 support
581
582 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
583 support
584
585 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
586 Extension support
587
588 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
589 Extension support
590
591 ataflop= [HW,M68k]
592
593 atarimouse= [HW,MOUSE] Atari Mouse
594
595 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
596 EzKey and similar keyboards
597
598 atkbd.reset= [HW] Reset keyboard during initialization
599
600 atkbd.set= [HW] Select keyboard code set
601 Format: <int> (2 = AT (default), 3 = PS/2)
602
603 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
604 keyboards
605
606 atkbd.softraw= [HW] Choose between synthetic and real raw mode
607 Format: <bool> (0 = real, 1 = synthetic (default))
608
609 atkbd.softrepeat= [HW]
610 Use software keyboard repeat
611
612 audit= [KNL] Enable the audit sub-system
613 Format: { "0" | "1" | "off" | "on" }
614 0 | off - kernel audit is disabled and can not be
615 enabled until the next reboot
616 unset - kernel audit is initialized but disabled and
617 will be fully enabled by the userspace auditd.
618 1 | on - kernel audit is initialized and partially
619 enabled, storing at most audit_backlog_limit
620 messages in RAM until it is fully enabled by the
621 userspace auditd.
622 Default: unset
623
624 audit_backlog_limit= [KNL] Set the audit queue size limit.
625 Format: <int> (must be >=0)
626 Default: 64
627
628 bau= [X86_UV] Enable the BAU on SGI UV. The default
629 behavior is to disable the BAU (i.e. bau=0).
630 Format: { "0" | "1" }
631 0 - Disable the BAU.
632 1 - Enable the BAU.
633 unset - Disable the BAU.
634
635 bdev_allow_write_mounted=
636 Format: <bool>
637 Control the ability to open a mounted block device
638 for writing, i.e., allow / disallow writes that bypass
639 the FS. This was implemented as a means to prevent
640 fuzzers from crashing the kernel by overwriting the
641 metadata underneath a mounted FS without its awareness.
642 This also prevents destructive formatting of mounted
643 filesystems by naive storage tooling that don't use
644 O_EXCL. Default is Y and can be changed through the
645 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED.
646
647 bert_disable [ACPI]
648 Disable BERT OS support on buggy BIOSes.
649
650 bgrt_disable [ACPI,X86,EARLY]
651 Disable BGRT to avoid flickering OEM logo.
652
653 blkdevparts= Manual partition parsing of block device(s) for
654 embedded devices based on command line input.
655 See Documentation/block/cmdline-partition.rst
656
657 boot_delay= [KNL,EARLY]
658 Milliseconds to delay each printk during boot.
659 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
660 and you may also have to specify "lpj=". Boot_delay
661 values larger than 10 seconds (10000) are assumed
662 erroneous and ignored.
663 Format: integer
664
665 bootconfig [KNL,EARLY]
666 Extended command line options can be added to an initrd
667 and this will cause the kernel to look for it.
668
669 See Documentation/admin-guide/bootconfig.rst
670
671 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
672 bttv.radio= Most important insmod options are available as
673 kernel args too.
674 bttv.pll= See Documentation/admin-guide/media/bttv.rst
675 bttv.tuner=
676
677 bulk_remove=off [PPC] This parameter disables the use of the pSeries
678 firmware feature for flushing multiple hpte entries
679 at a time.
680
681 c101= [NET] Moxa C101 synchronous serial card
682
683 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
684 Sometimes CPU hardware bugs make them report the cache
685 size incorrectly. The kernel will attempt work arounds
686 to fix known problems, but for some CPUs it is not
687 possible to determine what the correct size should be.
688 This option provides an override for these situations.
689
690 carrier_timeout=
691 [NET] Specifies amount of time (in seconds) that
692 the kernel should wait for a network carrier. By default
693 it waits 120 seconds.
694
695 ca_keys= [KEYS] This parameter identifies a specific key(s) on
696 the system trusted keyring to be used for certificate
697 trust validation.
698 format: { id:<keyid> | builtin }
699
700 cca= [MIPS,EARLY] Override the kernel pages' cache coherency
701 algorithm. Accepted values range from 0 to 7
702 inclusive. See arch/mips/include/asm/pgtable-bits.h
703 for platform specific values (SB1, Loongson3 and
704 others).
705
706 ccw_timeout_log [S390]
707 See Documentation/arch/s390/common_io.rst for details.
708
709 cfi= [X86-64] Set Control Flow Integrity checking features
710 when CONFIG_FINEIBT is enabled.
711 Format: feature[,feature...]
712 Default: auto
713
714 auto: Use FineIBT if IBT available, otherwise kCFI.
715 Under FineIBT, enable "paranoid" mode when
716 FRED is not available.
717 off: Turn off CFI checking.
718 kcfi: Use kCFI (disable FineIBT).
719 fineibt: Use FineIBT (even if IBT not available).
720 norand: Do not re-randomize CFI hashes.
721 paranoid: Add caller hash checking under FineIBT.
722 bhi: Enable register poisoning to stop speculation
723 across FineIBT. (Disabled by default.)
724 warn: Do not enforce CFI checking: warn only.
725 debug: Report CFI initialization details.
726
727 cgroup_disable= [KNL] Disable a particular controller or optional feature
728 Format: {name of the controller(s) or feature(s) to disable}
729 The effects of cgroup_disable=foo are:
730 - foo isn't auto-mounted if you mount all cgroups in
731 a single hierarchy
732 - foo isn't visible as an individually mountable
733 subsystem
734 - if foo is an optional feature then the feature is
735 disabled and corresponding cgroup files are not
736 created
737 {Currently only "memory" controller deal with this and
738 cut the overhead, others just disable the usage. So
739 only cgroup_disable=memory is actually worthy}
740 Specifying "pressure" disables per-cgroup pressure
741 stall information accounting feature
742
743 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
744 Format: { { controller | "all" | "named" }
745 [,{ controller | "all" | "named" }...] }
746 Like cgroup_disable, but only applies to cgroup v1;
747 the blacklisted controllers remain available in cgroup2.
748 "all" blacklists all controllers and "named" disables
749 named mounts. Specifying both "all" and "named" disables
750 all v1 hierarchies.
751
752 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups
753 Format: { "true" | "false" }
754 /proc/cgroups lists only v1 controllers by default.
755 This compatibility option enables listing also v2
756 controllers (whose v1 code is not compiled!), so that
757 semi-legacy software can check this file to decide
758 about usage of v2 (sic) controllers.
759
760 cgroup_favordynmods= [KNL] Enable or Disable favordynmods.
761 Format: { "true" | "false" }
762 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.
763
764 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
765 Format: <string>
766 nosocket -- Disable socket memory accounting.
767 nokmem -- Disable kernel memory accounting.
768 nobpf -- Disable BPF memory accounting.
769
770 check_pages= [MM,EARLY] Enable sanity checking of pages after
771 allocations / before freeing. This adds checks to catch
772 double-frees, use-after-frees, and other sources of
773 page corruption by inspecting page internals (flags,
774 mapcount/refcount, memcg_data, etc.).
775 Format: { "0" | "1" }
776 Default: 0 (1 if CONFIG_DEBUG_VM is set)
777
778 checkreqprot= [SELINUX] Set initial checkreqprot flag value.
779 Format: { "0" | "1" }
780 See security/selinux/Kconfig help text.
781 0 -- check protection applied by kernel (includes
782 any implied execute protection).
783 1 -- check protection requested by application.
784 Default value is set via a kernel config option.
785 Value can be changed at runtime via
786 /sys/fs/selinux/checkreqprot.
787 Setting checkreqprot to 1 is deprecated.
788
789 cio_ignore= [S390]
790 See Documentation/arch/s390/common_io.rst for details.
791
792 clearcpuid=X[,X...] [X86]
793 Disable CPUID feature X for the kernel. See
794 arch/x86/include/asm/cpufeatures.h for the valid bit
795 numbers X. Note the Linux-specific bits are not necessarily
796 stable over kernel options, but the vendor-specific
797 ones should be.
798 X can also be a string as appearing in the flags: line
799 in /proc/cpuinfo which does not have the above
800 instability issue. However, not all features have names
801 in /proc/cpuinfo.
802 Note that using this option will taint your kernel.
803 Also note that user programs calling CPUID directly
804 or using the feature without checking anything
805 will still see it. This just prevents it from
806 being used by the kernel or shown in /proc/cpuinfo.
807 Also note the kernel might malfunction if you disable
808 some critical bits.
809
810 clk_ignore_unused
811 [CLK]
812 Prevents the clock framework from automatically gating
813 clocks that have not been explicitly enabled by a Linux
814 device driver but are enabled in hardware at reset or
815 by the bootloader/firmware. Note that this does not
816 force such clocks to be always-on nor does it reserve
817 those clocks in any way. This parameter is useful for
818 debug and development, but should not be needed on a
819 platform with proper driver support. For more
820 information, see Documentation/driver-api/clk.rst.
821
822 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
823 [Deprecated]
824 Forces specified clocksource (if available) to be used
825 when calculating gettimeofday(). If specified
826 clocksource is not available, it defaults to PIT.
827 Format: { pit | tsc | cyclone | pmtmr }
828
829 clocksource= Override the default clocksource
830 Format: <string>
831 Override the default clocksource and use the clocksource
832 with the name specified.
833 Some clocksource names to choose from, depending on
834 the platform:
835 [all] jiffies (this is the base, fallback clocksource)
836 [ACPI] acpi_pm
837 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
838 pxa_timer,timer3,32k_counter,timer0_1
839 [X86-32] pit,hpet,tsc;
840 scx200_hrt on Geode; cyclone on IBM x440
841 [MIPS] MIPS
842 [PARISC] cr16
843 [S390] tod
844 [SH] SuperH
845 [SPARC64] tick
846 [X86-64] hpet,tsc
847
848 clocksource.arm_arch_timer.evtstrm=
849 [ARM,ARM64,EARLY]
850 Format: <bool>
851 Enable/disable the eventstream feature of the ARM
852 architected timer so that code using WFE-based polling
853 loops can be debugged more effectively on production
854 systems.
855
856 clocksource.verify_n_cpus= [KNL]
857 Limit the number of CPUs checked for clocksources
858 marked with CLOCK_SOURCE_VERIFY_PERCPU that
859 are marked unstable due to excessive skew.
860 A negative value says to check all CPUs, while
861 zero says not to check any. Values larger than
862 nr_cpu_ids are silently truncated to nr_cpu_ids.
863 The actual CPUs are chosen randomly, with
864 no replacement if the same CPU is chosen twice.
865
866 clocksource-wdtest.holdoff= [KNL]
867 Set the time in seconds that the clocksource
868 watchdog test waits before commencing its tests.
869 Defaults to zero when built as a module and to
870 10 seconds when built into the kernel.
871
872 cma=nn[MG]@[start[MG][-end[MG]]]
873 [KNL,CMA,EARLY]
874 Sets the size of kernel global memory area for
875 contiguous memory allocations and optionally the
876 placement constraint by the physical address range of
877 memory allocations. A value of 0 disables CMA
878 altogether. For more information, see
879 kernel/dma/contiguous.c
880
881 cma_pernuma=nn[MG]
882 [KNL,CMA,EARLY]
883 Sets the size of kernel per-numa memory area for
884 contiguous memory allocations. A value of 0 disables
885 per-numa CMA altogether. And If this option is not
886 specified, the default value is 0.
887 With per-numa CMA enabled, DMA users on node nid will
888 first try to allocate buffer from the pernuma area
889 which is located in node nid, if the allocation fails,
890 they will fallback to the global default memory area.
891
892 numa_cma=<node>:nn[MG][,<node>:nn[MG]]
893 [KNL,CMA,EARLY]
894 Sets the size of kernel numa memory area for
895 contiguous memory allocations. It will reserve CMA
896 area for the specified node.
897
898 With numa CMA enabled, DMA users on node nid will
899 first try to allocate buffer from the numa area
900 which is located in node nid, if the allocation fails,
901 they will fallback to the global default memory area.
902
903 cmo_free_hint= [PPC] Format: { yes | no }
904 Specify whether pages are marked as being inactive
905 when they are freed. This is used in CMO environments
906 to determine OS memory pressure for page stealing by
907 a hypervisor.
908 Default: yes
909
910 coherent_pool=nn[KMG] [ARM,KNL,EARLY]
911 Sets the size of memory pool for coherent, atomic dma
912 allocations, by default set to 256K.
913
914 com20020= [HW,NET] ARCnet - COM20020 chipset
915 Format:
916 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
917
918 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
919 Format: <io>[,<irq>]
920
921 com90xx= [HW,NET]
922 ARCnet - COM90xx chipset (memory-mapped buffers)
923 Format: <io>[,<irq>[,<memstart>]]
924
925 condev= [HW,S390] console device
926 conmode=
927
928 con3215_drop= [S390,EARLY] 3215 console drop mode.
929 Format: y|n|Y|N|1|0
930 When set to true, drop data on the 3215 console when
931 the console buffer is full. In this case the
932 operator using a 3270 terminal emulator (for example
933 x3270) does not have to enter the clear key for the
934 console output to advance and the kernel to continue.
935 This leads to a much faster boot time when a 3270
936 terminal emulator is active. If no 3270 terminal
937 emulator is used, this parameter has no effect.
938
939 console= [KNL] Output console device and options.
940
941 tty<n> Use the virtual console device <n>.
942
943 ttyS<n>[,options]
944 ttyUSB0[,options]
945 Use the specified serial port. The options are of
946 the form "bbbbpnf", where "bbbb" is the baud rate,
947 "p" is parity ("n", "o", or "e"), "n" is number of
948 bits, and "f" is flow control ("r" for RTS or
949 omit it). Default is "9600n8".
950
951 See Documentation/admin-guide/serial-console.rst for more
952 information. See
953 Documentation/networking/netconsole.rst for an
954 alternative.
955
956 <DEVNAME>:<n>.<n>[,options]
957 Use the specified serial port on the serial core bus.
958 The addressing uses DEVNAME of the physical serial port
959 device, followed by the serial core controller instance,
960 and the serial port instance. The options are the same
961 as documented for the ttyS addressing above.
962
963 The mapping of the serial ports to the tty instances
964 can be viewed with:
965
966 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/*
967 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0
968
969 In the above example, the console can be addressed with
970 console=00:04:0.0. Note that a console addressed this
971 way will only get added when the related device driver
972 is ready. The use of an earlycon parameter in addition to
973 the console may be desired for console output early on.
974
975 uart[8250],io,<addr>[,options]
976 uart[8250],mmio,<addr>[,options]
977 uart[8250],mmio16,<addr>[,options]
978 uart[8250],mmio32,<addr>[,options]
979 uart[8250],0x<addr>[,options]
980 Start an early, polled-mode console on the 8250/16550
981 UART at the specified I/O port or MMIO address,
982 switching to the matching ttyS device later.
983 MMIO inter-register address stride is either 8-bit
984 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
985 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
986 to be equivalent to 'mmio'. 'options' are specified in
987 the same format described for ttyS above; if unspecified,
988 the h/w is not re-initialized.
989
990 hvc<n> Use the hypervisor console device <n>. This is for
991 both Xen and PowerPC hypervisors.
992
993 { null | "" }
994 Use to disable console output, i.e., to have kernel
995 console messages discarded.
996 This must be the only console= parameter used on the
997 kernel command line.
998
999 If the device connected to the port is not a TTY but a braille
1000 device, prepend "brl," before the device type, for instance
1001 console=brl,ttyS0
1002 For now, only VisioBraille is supported.
1003
1004 console_msg_format=
1005 [KNL] Change console messages format
1006 default
1007 By default we print messages on consoles in
1008 "[time stamp] text\n" format (time stamp may not be
1009 printed, depending on CONFIG_PRINTK_TIME or
1010 `printk_time' param).
1011 syslog
1012 Switch to syslog format: "<%u>[time stamp] text\n"
1013 IOW, each message will have a facility and loglevel
1014 prefix. The format is similar to one used by syslog()
1015 syscall, or to executing "dmesg -S --raw" or to reading
1016 from /proc/kmsg.
1017
1018 consoleblank= [KNL] The console blank (screen saver) timeout in
1019 seconds. A value of 0 disables the blank timer.
1020 Defaults to 0.
1021
1022 coredump_filter=
1023 [KNL] Change the default value for
1024 /proc/<pid>/coredump_filter.
1025 See also Documentation/filesystems/proc.rst.
1026
1027 coresight_cpu_debug.enable
1028 [ARM,ARM64]
1029 Format: <bool>
1030 Enable/disable the CPU sampling based debugging.
1031 0: default value, disable debugging
1032 1: enable debugging at boot time
1033
1034 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
1035 Format:
1036 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
1037
1038 cpuidle.off=1 [CPU_IDLE]
1039 disable the cpuidle sub-system
1040
1041 cpuidle.governor=
1042 [CPU_IDLE] Name of the cpuidle governor to use.
1043
1044 cpufreq.off=1 [CPU_FREQ]
1045 disable the cpufreq sub-system
1046
1047 cpufreq.default_governor=
1048 [CPU_FREQ] Name of the default cpufreq governor or
1049 policy to use. This governor must be registered in the
1050 kernel before the cpufreq driver probes.
1051
1052 cpu_init_udelay=N
1053 [X86,EARLY] Delay for N microsec between assert and de-assert
1054 of APIC INIT to start processors. This delay occurs
1055 on every CPU online, such as boot, and resume from suspend.
1056 Default: 10000
1057
1058 cpuhp.parallel=
1059 [SMP] Enable/disable parallel bringup of secondary CPUs
1060 Format: <bool>
1061 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise
1062 the parameter has no effect.
1063
1064 crash_kexec_post_notifiers
1065 Only jump to kdump kernel after running the panic
1066 notifiers and dumping kmsg. This option increases
1067 the risks of a kdump failure, since some panic
1068 notifiers can make the crashed kernel more unstable.
1069 In configurations where kdump may not be reliable,
1070 running the panic notifiers could allow collecting
1071 more data on dmesg, like stack traces from other CPUS
1072 or extra data dumped by panic_print. Note that some
1073 configurations enable this option unconditionally,
1074 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP.
1075
1076 crashkernel=size[KMG][@offset[KMG]]
1077 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'
1078 upon panic. This parameter reserves the physical
1079 memory region [offset, offset + size] for that kernel
1080 image. If '@offset' is omitted, then a suitable offset
1081 is selected automatically.
1082 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region
1083 under 4G first, and fall back to reserve region above
1084 4G when '@offset' hasn't been specified.
1085 See Documentation/admin-guide/kdump/kdump.rst for further details.
1086
1087 crashkernel=range1:size1[,range2:size2,...][@offset]
1088 [KNL] Same as above, but depends on the memory
1089 in the running system. The syntax of range is
1090 start-[end] where start and end are both
1091 a memory unit (amount[KMG]). See also
1092 Documentation/admin-guide/kdump/kdump.rst for an example.
1093
1094 crashkernel=size[KMG],high
1095 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be
1096 above 4G.
1097 Allow kernel to allocate physical memory region from top,
1098 so could be above 4G if system have more than 4G ram
1099 installed. Otherwise memory region will be allocated
1100 below 4G, if available.
1101 It will be ignored if crashkernel=X is specified.
1102 crashkernel=size[KMG],low
1103 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G.
1104 When crashkernel=X,high is passed, kernel could allocate
1105 physical memory region above 4G, that cause second kernel
1106 crash on system that require some amount of low memory,
1107 e.g. swiotlb requires at least 64M+32K low memory, also
1108 enough extra low memory is needed to make sure DMA buffers
1109 for 32-bit devices won't run out. Kernel would try to allocate
1110 default size of memory below 4G automatically. The default
1111 size is platform dependent.
1112 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)
1113 --> arm64: 128MiB
1114 --> riscv: 128MiB
1115 --> loongarch: 128MiB
1116 This one lets the user specify own low range under 4G
1117 for second kernel instead.
1118 0: to disable low allocation.
1119 It will be ignored when crashkernel=X,high is not used
1120 or memory reserved is below 4G.
1121 crashkernel=size[KMG],cma
1122 [KNL, X86, ppc] Reserve additional crash kernel memory from
1123 CMA. This reservation is usable by the first system's
1124 userspace memory and kernel movable allocations (memory
1125 balloon, zswap). Pages allocated from this memory range
1126 will not be included in the vmcore so this should not
1127 be used if dumping of userspace memory is intended and
1128 it has to be expected that some movable kernel pages
1129 may be missing from the dump.
1130
1131 A standard crashkernel reservation, as described above,
1132 is still needed to hold the crash kernel and initrd.
1133
1134 This option increases the risk of a kdump failure: DMA
1135 transfers configured by the first kernel may end up
1136 corrupting the second kernel's memory.
1137
1138 This reservation method is intended for systems that
1139 can't afford to sacrifice enough memory for standard
1140 crashkernel reservation and where less reliable and
1141 possibly incomplete kdump is preferable to no kdump at
1142 all.
1143
1144 cryptomgr.notests
1145 [KNL] Disable crypto self-tests
1146
1147 cs89x0_dma= [HW,NET]
1148 Format: <dma>
1149
1150 cs89x0_media= [HW,NET]
1151 Format: { rj45 | aui | bnc }
1152
1153 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU
1154 function call handling. When switched on,
1155 additional debug data is printed to the console
1156 in case a hanging CPU is detected, and that
1157 CPU is pinged again in order to try to resolve
1158 the hang situation. The default value of this
1159 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
1160 Kconfig option.
1161
1162 dasd= [HW,NET]
1163 See header of drivers/s390/block/dasd_devmap.c.
1164
1165 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
1166 (one device per port)
1167 Format: <port#>,<type>
1168 See also Documentation/input/devices/joystick-parport.rst
1169
1170 debug [KNL,EARLY] Enable kernel debugging (events log level).
1171
1172 debug_boot_weak_hash
1173 [KNL,EARLY] Enable printing [hashed] pointers early in the
1174 boot sequence. If enabled, we use a weak hash instead
1175 of siphash to hash pointers. Use this option if you are
1176 seeing instances of '(___ptrval___)') and need to see a
1177 value (hashed pointer) instead. Cryptographically
1178 insecure, please do not use on production kernels.
1179
1180 debug_locks_verbose=
1181 [KNL] verbose locking self-tests
1182 Format: <int>
1183 Print debugging info while doing the locking API
1184 self-tests.
1185 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
1186 (no extra messages), setting it to -1 (all bits set)
1187 will print _a_lot_ more information - normally only
1188 useful to lockdep developers.
1189
1190 debug_objects [KNL,EARLY] Enable object debugging
1191
1192 debug_guardpage_minorder=
1193 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this
1194 parameter allows control of the order of pages that will
1195 be intentionally kept free (and hence protected) by the
1196 buddy allocator. Bigger value increase the probability
1197 of catching random memory corruption, but reduce the
1198 amount of memory for normal system use. The maximum
1199 possible value is MAX_PAGE_ORDER/2. Setting this
1200 parameter to 1 or 2 should be enough to identify most
1201 random memory corruption problems caused by bugs in
1202 kernel or driver code when a CPU writes to (or reads
1203 from) a random memory location. Note that there exists
1204 a class of memory corruptions problems caused by buggy
1205 H/W or F/W or by drivers badly programming DMA
1206 (basically when memory is written at bus level and the
1207 CPU MMU is bypassed) which are not detectable by
1208 CONFIG_DEBUG_PAGEALLOC, hence this option will not
1209 help tracking down these problems.
1210
1211 debug_pagealloc=
1212 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
1213 enables the feature at boot time. By default, it is
1214 disabled and the system will work mostly the same as a
1215 kernel built without CONFIG_DEBUG_PAGEALLOC.
1216 Note: to get most of debug_pagealloc error reports, it's
1217 useful to also enable the page_owner functionality.
1218 on: enable the feature
1219
1220 debugfs= [KNL,EARLY] This parameter enables what is exposed to
1221 userspace and debugfs internal clients.
1222 Format: { on, off }
1223 on: All functions are enabled.
1224 off: Filesystem is not registered and clients
1225 get a -EPERM as result when trying to register files
1226 or directories within debugfs.
1227 This is equivalent of the runtime functionality if
1228 debugfs was not enabled in the kernel at all.
1229 Default value is set in build-time with a kernel configuration.
1230
1231 debugpat [X86] Enable PAT debugging
1232
1233 default_hugepagesz=
1234 [HW] The size of the default HugeTLB page. This is
1235 the size represented by the legacy /proc/ hugepages
1236 APIs. In addition, this is the default hugetlb size
1237 used for shmget(), mmap() and mounting hugetlbfs
1238 filesystems. If not specified, defaults to the
1239 architecture's default huge page size. Huge page
1240 sizes are architecture dependent. See also
1241 Documentation/admin-guide/mm/hugetlbpage.rst.
1242 Format: size[KMG]
1243
1244 deferred_probe_timeout=
1245 [KNL] Debugging option to set a timeout in seconds for
1246 deferred probe to give up waiting on dependencies to
1247 probe. Only specific dependencies (subsystems or
1248 drivers) that have opted in will be ignored. A timeout
1249 of 0 will timeout at the end of initcalls. If the time
1250 out hasn't expired, it'll be restarted by each
1251 successful driver registration. This option will also
1252 dump out devices still on the deferred probe list after
1253 retrying.
1254
1255 delayacct [KNL] Enable per-task delay accounting
1256
1257 dell_smm_hwmon.ignore_dmi=
1258 [HW] Continue probing hardware even if DMI data
1259 indicates that the driver is running on unsupported
1260 hardware.
1261
1262 dell_smm_hwmon.force=
1263 [HW] Activate driver even if SMM BIOS signature does
1264 not match list of supported models and enable otherwise
1265 blacklisted features.
1266
1267 dell_smm_hwmon.power_status=
1268 [HW] Report power status in /proc/i8k
1269 (disabled by default).
1270
1271 dell_smm_hwmon.restricted=
1272 [HW] Allow controlling fans only if SYS_ADMIN
1273 capability is set.
1274
1275 dell_smm_hwmon.fan_mult=
1276 [HW] Factor to multiply fan speed with.
1277
1278 dell_smm_hwmon.fan_max=
1279 [HW] Maximum configurable fan speed.
1280
1281 dfltcc= [HW,S390]
1282 Format: { on | off | def_only | inf_only | always }
1283 on: s390 zlib hardware support for compression on
1284 level 1 and decompression (default)
1285 off: No s390 zlib hardware support
1286 def_only: s390 zlib hardware support for deflate
1287 only (compression on level 1)
1288 inf_only: s390 zlib hardware support for inflate
1289 only (decompression)
1290 always: Same as 'on' but ignores the selected compression
1291 level always using hardware support (used for debugging)
1292
1293 dhash_entries= [KNL]
1294 Set number of hash buckets for dentry cache.
1295
1296 disable_1tb_segments [PPC,EARLY]
1297 Disables the use of 1TB hash page table segments. This
1298 causes the kernel to fall back to 256MB segments which
1299 can be useful when debugging issues that require an SLB
1300 miss to occur.
1301
1302 disable= [IPV6]
1303 See Documentation/networking/ipv6.rst.
1304
1305 disable_radix [PPC,EARLY]
1306 Disable RADIX MMU mode on POWER9
1307
1308 disable_tlbie [PPC]
1309 Disable TLBIE instruction. Currently does not work
1310 with KVM, with HASH MMU, or with coherent accelerators.
1311
1312 disable_ddw [PPC/PSERIES,EARLY]
1313 Disable Dynamic DMA Window support. Use this
1314 to workaround buggy firmware.
1315
1316 disable_ipv6= [IPV6]
1317 See Documentation/networking/ipv6.rst.
1318
1319 disable_mtrr_cleanup [X86,EARLY]
1320 The kernel tries to adjust MTRR layout from continuous
1321 to discrete, to make X server driver able to add WB
1322 entry later. This parameter disables that.
1323
1324 disable_mtrr_trim [X86, Intel and AMD only,EARLY]
1325 By default the kernel will trim any uncacheable
1326 memory out of your available memory pool based on
1327 MTRR settings. This parameter disables that behavior,
1328 possibly causing your machine to run very slowly.
1329
1330 disable_timer_pin_1 [X86,EARLY]
1331 Disable PIN 1 of APIC timer
1332 Can be useful to work around chipset bugs.
1333
1334 dis_ucode_ldr [X86] Disable the microcode loader.
1335
1336 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1337 this option disables the debugging code at boot.
1338
1339 dma_debug_entries=<number>
1340 This option allows to tune the number of preallocated
1341 entries for DMA-API debugging code. One entry is
1342 required per DMA-API allocation. Use this if the
1343 DMA-API debugging code disables itself because the
1344 architectural default is too low.
1345
1346 dma_debug_driver=<driver_name>
1347 With this option the DMA-API debugging driver
1348 filter feature can be enabled at boot time. Just
1349 pass the driver to filter for as the parameter.
1350 The filter can be disabled or changed to another
1351 driver later using sysfs.
1352
1353 reg_file_data_sampling=
1354 [X86] Controls mitigation for Register File Data
1355 Sampling (RFDS) vulnerability. RFDS is a CPU
1356 vulnerability which may allow userspace to infer
1357 kernel data values previously stored in floating point
1358 registers, vector registers, or integer registers.
1359 RFDS only affects Intel Atom processors.
1360
1361 on: Turns ON the mitigation.
1362 off: Turns OFF the mitigation.
1363
1364 This parameter overrides the compile time default set
1365 by CONFIG_MITIGATION_RFDS. Mitigation cannot be
1366 disabled when other VERW based mitigations (like MDS)
1367 are enabled. In order to disable RFDS mitigation all
1368 VERW based mitigations need to be disabled.
1369
1370 For details see:
1371 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
1372
1373 dm_verity.keyring_unsealed=
1374 [KNL] When set to 1, leave the dm-verity keyring
1375 unsealed after initialization so userspace can
1376 provision keys. Once the keyring is restricted
1377 it becomes active and is searched during signature
1378 verification.
1379
1380 driver_async_probe= [KNL]
1381 List of driver names to be probed asynchronously. *
1382 matches with all driver names. If * is specified, the
1383 rest of the listed driver names are those that will NOT
1384 match the *.
1385 Format: <driver_name1>,<driver_name2>...
1386
1387 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1388 Broken monitors, graphic adapters, KVMs and EDIDless
1389 panels may send no or incorrect EDID data sets.
1390 This parameter allows to specify an EDID data sets
1391 in the /lib/firmware directory that are used instead.
1392 An EDID data set will only be used for a particular
1393 connector, if its name and a colon are prepended to
1394 the EDID name. Each connector may use a unique EDID
1395 data set by separating the files with a comma. An EDID
1396 data set with no connector name will be used for
1397 any connectors not explicitly specified.
1398
1399 dscc4.setup= [NET]
1400
1401 dt_cpu_ftrs= [PPC,EARLY]
1402 Format: {"off" | "known"}
1403 Control how the dt_cpu_ftrs device-tree binding is
1404 used for CPU feature discovery and setup (if it
1405 exists).
1406 off: Do not use it, fall back to legacy cpu table.
1407 known: Do not pass through unknown features to guests
1408 or userspace, only those that the kernel is aware of.
1409
1410 dump_apple_properties [X86]
1411 Dump name and content of EFI device properties on
1412 x86 Macs. Useful for driver authors to determine
1413 what data is available or for reverse-engineering.
1414
1415 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1416 <module>.dyndbg[="val"]
1417 Enable debug messages at boot time. See
1418 Documentation/admin-guide/dynamic-debug-howto.rst
1419 for details.
1420
1421 early_ioremap_debug [KNL,EARLY]
1422 Enable debug messages in early_ioremap support. This
1423 is useful for tracking down temporary early mappings
1424 which are not unmapped.
1425
1426 earlycon= [KNL,EARLY] Output early console device and options.
1427
1428 When used with no options, the early console is
1429 determined by stdout-path property in device tree's
1430 chosen node or the ACPI SPCR table if supported by
1431 the platform.
1432
1433 cdns,<addr>[,options]
1434 Start an early, polled-mode console on a Cadence
1435 (xuartps) serial port at the specified address. Only
1436 supported option is baud rate. If baud rate is not
1437 specified, the serial port must already be setup and
1438 configured.
1439
1440 uart[8250],io,<addr>[,options[,uartclk]]
1441 uart[8250],mmio,<addr>[,options[,uartclk]]
1442 uart[8250],mmio32,<addr>[,options[,uartclk]]
1443 uart[8250],mmio32be,<addr>[,options[,uartclk]]
1444 uart[8250],0x<addr>[,options]
1445 Start an early, polled-mode console on the 8250/16550
1446 UART at the specified I/O port or MMIO address.
1447 MMIO inter-register address stride is either 8-bit
1448 (mmio) or 32-bit (mmio32 or mmio32be).
1449 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1450 to be equivalent to 'mmio'. 'options' are specified
1451 in the same format described for "console=ttyS<n>"; if
1452 unspecified, the h/w is not initialized. 'uartclk' is
1453 the uart clock frequency; if unspecified, it is set
1454 to 'BASE_BAUD' * 16.
1455
1456 pl011,<addr>
1457 pl011,mmio32,<addr>
1458 Start an early, polled-mode console on a pl011 serial
1459 port at the specified address. The pl011 serial port
1460 must already be setup and configured. Options are not
1461 yet supported. If 'mmio32' is specified, then only
1462 the driver will use only 32-bit accessors to read/write
1463 the device registers.
1464
1465 liteuart,<addr>
1466 Start an early console on a litex serial port at the
1467 specified address. The serial port must already be
1468 setup and configured. Options are not yet supported.
1469
1470 meson,<addr>
1471 Start an early, polled-mode console on a meson serial
1472 port at the specified address. The serial port must
1473 already be setup and configured. Options are not yet
1474 supported.
1475
1476 msm_serial,<addr>
1477 Start an early, polled-mode console on an msm serial
1478 port at the specified address. The serial port
1479 must already be setup and configured. Options are not
1480 yet supported.
1481
1482 msm_serial_dm,<addr>
1483 Start an early, polled-mode console on an msm serial
1484 dm port at the specified address. The serial port
1485 must already be setup and configured. Options are not
1486 yet supported.
1487
1488 owl,<addr>
1489 Start an early, polled-mode console on a serial port
1490 of an Actions Semi SoC, such as S500 or S900, at the
1491 specified address. The serial port must already be
1492 setup and configured. Options are not yet supported.
1493
1494 rda,<addr>
1495 Start an early, polled-mode console on a serial port
1496 of an RDA Micro SoC, such as RDA8810PL, at the
1497 specified address. The serial port must already be
1498 setup and configured. Options are not yet supported.
1499
1500 sbi
1501 Use RISC-V SBI (Supervisor Binary Interface) for early
1502 console.
1503
1504 smh Use ARM semihosting calls for early console.
1505
1506 s3c2410,<addr>
1507 s3c2412,<addr>
1508 s3c2440,<addr>
1509 s3c6400,<addr>
1510 s5pv210,<addr>
1511 exynos4210,<addr>
1512 Use early console provided by serial driver available
1513 on Samsung SoCs, requires selecting proper type and
1514 a correct base address of the selected UART port. The
1515 serial port must already be setup and configured.
1516 Options are not yet supported.
1517
1518 lantiq,<addr>
1519 Start an early, polled-mode console on a lantiq serial
1520 (lqasc) port at the specified address. The serial port
1521 must already be setup and configured. Options are not
1522 yet supported.
1523
1524 lpuart,<addr>
1525 lpuart32,<addr>
1526 Use early console provided by Freescale LP UART driver
1527 found on Freescale Vybrid and QorIQ LS1021A processors.
1528 A valid base address must be provided, and the serial
1529 port must already be setup and configured.
1530
1531 ec_imx21,<addr>
1532 ec_imx6q,<addr>
1533 Start an early, polled-mode, output-only console on the
1534 Freescale i.MX UART at the specified address. The UART
1535 must already be setup and configured.
1536
1537 ar3700_uart,<addr>
1538 Start an early, polled-mode console on the
1539 Armada 3700 serial port at the specified
1540 address. The serial port must already be setup
1541 and configured. Options are not yet supported.
1542
1543 qcom_geni,<addr>
1544 Start an early, polled-mode console on a Qualcomm
1545 Generic Interface (GENI) based serial port at the
1546 specified address. The serial port must already be
1547 setup and configured. Options are not yet supported.
1548
1549 efifb,[options]
1550 Start an early, unaccelerated console on the EFI
1551 memory mapped framebuffer (if available). On cache
1552 coherent non-x86 systems that use system memory for
1553 the framebuffer, pass the 'ram' option so that it is
1554 mapped with the correct attributes.
1555
1556 linflex,<addr>
1557 Use early console provided by Freescale LINFlexD UART
1558 serial driver for NXP S32V234 SoCs. A valid base
1559 address must be provided, and the serial port must
1560 already be setup and configured.
1561
1562 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY]
1563 earlyprintk=vga
1564 earlyprintk=sclp
1565 earlyprintk=xen
1566 earlyprintk=serial[,ttySn[,baudrate]]
1567 earlyprintk=serial[,0x...[,baudrate]]
1568 earlyprintk=ttySn[,baudrate]
1569 earlyprintk=dbgp[debugController#]
1570 earlyprintk=mmio32,membase[,{nocfg|baudrate}]
1571 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}]
1572 earlyprintk=xdbc[xhciController#]
1573 earlyprintk=bios
1574
1575 earlyprintk is useful when the kernel crashes before
1576 the normal console is initialized. It is not enabled by
1577 default because it has some cosmetic problems.
1578
1579 Use "nocfg" to skip UART configuration, assume
1580 BIOS/firmware has configured UART correctly.
1581
1582 Append ",keep" to not disable it when the real console
1583 takes over.
1584
1585 Only one of vga, serial, or usb debug port can
1586 be used at a time.
1587
1588 Currently only ttyS0 and ttyS1 may be specified by
1589 name. Other I/O ports may be explicitly specified
1590 on some architectures (x86 and arm at least) by
1591 replacing ttySn with an I/O port address, like this:
1592 earlyprintk=serial,0x1008,115200
1593 You can find the port for a given device in
1594 /proc/tty/driver/serial:
1595 2: uart:ST16650V2 port:00001008 irq:18 ...
1596
1597 Interaction with the standard serial driver is not
1598 very good.
1599
1600 The VGA output is eventually overwritten by
1601 the real console.
1602
1603 The xen option can only be used in Xen domains.
1604
1605 The sclp output can only be used on s390.
1606
1607 The bios output can only be used on SuperH.
1608
1609 The optional "force" to "pciserial" enables use of a
1610 PCI device even when its classcode is not of the
1611 UART class.
1612
1613 edac_report= [HW,EDAC] Control how to report EDAC event
1614 Format: {"on" | "off" | "force"}
1615 on: enable EDAC to report H/W event. May be overridden
1616 by other higher priority error reporting module.
1617 off: disable H/W event reporting through EDAC.
1618 force: enforce the use of EDAC to report H/W event.
1619 default: on.
1620
1621 edd= [EDD]
1622 Format: {"off" | "on" | "skip[mbr]"}
1623
1624 efi= [EFI,EARLY]
1625 Format: { "debug", "disable_early_pci_dma",
1626 "nochunk", "noruntime", "nosoftreserve",
1627 "novamap", "no_disable_early_pci_dma" }
1628 debug: enable misc debug output.
1629 disable_early_pci_dma: disable the busmaster bit on all
1630 PCI bridges while in the EFI boot stub.
1631 nochunk: disable reading files in "chunks" in the EFI
1632 boot stub, as chunking can cause problems with some
1633 firmware implementations.
1634 noruntime : disable EFI runtime services support
1635 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1636 attribute may cause the kernel to reserve the
1637 memory range for a memory mapping driver to
1638 claim. Specify efi=nosoftreserve to disable this
1639 reservation and treat the memory by its base type
1640 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1641 novamap: do not call SetVirtualAddressMap().
1642 no_disable_early_pci_dma: Leave the busmaster bit set
1643 on all PCI bridges while in the EFI boot stub
1644
1645 efi_no_storage_paranoia [EFI,X86,EARLY]
1646 Using this parameter you can use more than 50% of
1647 your efi variable storage. Use this parameter only if
1648 you are really sure that your UEFI does sane gc and
1649 fulfills the spec otherwise your board may brick.
1650
1651 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1652 that is to be dynamically loaded by Linux. If there are
1653 multiple variables with the same name but with different
1654 vendor GUIDs, all of them will be loaded. See
1655 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1656
1657
1658 eisa_irq_edge= [PARISC,HW]
1659 See header of drivers/parisc/eisa.c.
1660
1661 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging
1662 Format: ekgdboc=kbd
1663
1664 This is designed to be used in conjunction with
1665 the boot argument: earlyprintk=vga
1666
1667 This parameter works in place of the kgdboc parameter
1668 but can only be used if the backing tty is available
1669 very early in the boot process. For early debugging
1670 via a serial port see kgdboc_earlycon instead.
1671
1672 elanfreq= [X86-32]
1673 See comment before function elanfreq_setup() in
1674 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1675
1676 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY]
1677 Specifies physical address of start of kernel core
1678 image elf header and optionally the size. Generally
1679 kexec loader will pass this option to capture kernel.
1680 See Documentation/admin-guide/kdump/kdump.rst for details.
1681
1682 enable_mtrr_cleanup [X86,EARLY]
1683 The kernel tries to adjust MTRR layout from continuous
1684 to discrete, to make X server driver able to add WB
1685 entry later. This parameter enables that.
1686
1687 enable_timer_pin_1 [X86]
1688 Enable PIN 1 of APIC timer
1689 Can be useful to work around chipset bugs
1690 (in particular on some ATI chipsets).
1691 The kernel tries to set a reasonable default.
1692
1693 enforcing= [SELINUX] Set initial enforcing status.
1694 Format: {"0" | "1"}
1695 See security/selinux/Kconfig help text.
1696 0 -- permissive (log only, no denials).
1697 1 -- enforcing (deny and log).
1698 Default value is 0.
1699 Value can be changed at runtime via
1700 /sys/fs/selinux/enforce.
1701
1702 erst_disable [ACPI]
1703 Disable Error Record Serialization Table (ERST)
1704 support.
1705
1706 ether= [HW,NET] Ethernet cards parameters
1707 This option is obsoleted by the "netdev=" option, which
1708 has equivalent usage. See its documentation for details.
1709
1710 evm= [EVM]
1711 Format: { "fix" }
1712 Permit 'security.evm' to be updated regardless of
1713 current integrity status.
1714
1715 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier
1716 stages so cover more early boot allocations.
1717 Please note that as side effect some optimizations
1718 might be disabled to achieve that (e.g. parallelized
1719 memory initialization is disabled) so the boot process
1720 might take longer, especially on systems with a lot of
1721 memory. Available with CONFIG_PAGE_EXTENSION=y.
1722
1723 failslab=
1724 fail_usercopy=
1725 fail_page_alloc=
1726 fail_skb_realloc=
1727 fail_make_request=[KNL]
1728 General fault injection mechanism.
1729 Format: <interval>,<probability>,<space>,<times>
1730 See also Documentation/fault-injection/.
1731
1732 fb_tunnels= [NET]
1733 Format: { initns | none }
1734 See Documentation/admin-guide/sysctl/net.rst for
1735 fb_tunnels_only_for_init_ns
1736
1737 floppy= [HW]
1738 See Documentation/admin-guide/blockdev/floppy.rst.
1739
1740 forcepae [X86-32]
1741 Forcefully enable Physical Address Extension (PAE).
1742 Many Pentium M systems disable PAE but may have a
1743 functionally usable PAE implementation.
1744 Warning: use of this parameter will taint the kernel
1745 and may cause unknown problems.
1746
1747 fred= [X86-64]
1748 Enable/disable Flexible Return and Event Delivery.
1749 Format: { on | off }
1750 on: enable FRED when it's present, the default setting.
1751 off: disable FRED.
1752
1753 ftrace=[tracer]
1754 [FTRACE] will set and start the specified tracer
1755 as early as possible in order to facilitate early
1756 boot debugging.
1757
1758 ftrace_boot_snapshot
1759 [FTRACE] On boot up, a snapshot will be taken of the
1760 ftrace ring buffer that can be read at:
1761 /sys/kernel/tracing/snapshot.
1762 This is useful if you need tracing information from kernel
1763 boot up that is likely to be overridden by user space
1764 start up functionality.
1765
1766 Optionally, the snapshot can also be defined for a tracing
1767 instance that was created by the trace_instance= command
1768 line parameter.
1769
1770 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
1771
1772 The above will cause the "foo" tracing instance to trigger
1773 a snapshot at the end of boot up.
1774
1775 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> |
1776 ,<instance>=2(orig_cpu)]
1777 [FTRACE] will dump the trace buffers on oops.
1778 If no parameter is passed, ftrace will dump global
1779 buffers of all CPUs, if you pass 2 or orig_cpu, it
1780 will dump only the buffer of the CPU that triggered
1781 the oops, or the specific instance will be dumped if
1782 its name is passed. Multiple instance dump is also
1783 supported, and instances are separated by commas. Each
1784 instance supports only dump on CPU that triggered the
1785 oops by passing 2 or orig_cpu to it.
1786
1787 ftrace_dump_on_oops=foo=orig_cpu
1788
1789 The above will dump only the buffer of "foo" instance
1790 on CPU that triggered the oops.
1791
1792 ftrace_dump_on_oops,foo,bar=orig_cpu
1793
1794 The above will dump global buffer on all CPUs, the
1795 buffer of "foo" instance on all CPUs and the buffer
1796 of "bar" instance on CPU that triggered the oops.
1797
1798 ftrace_filter=[function-list]
1799 [FTRACE] Limit the functions traced by the function
1800 tracer at boot up. function-list is a comma-separated
1801 list of functions. This list can be changed at run
1802 time by the set_ftrace_filter file in the debugfs
1803 tracing directory.
1804
1805 ftrace_notrace=[function-list]
1806 [FTRACE] Do not trace the functions specified in
1807 function-list. This list can be changed at run time
1808 by the set_ftrace_notrace file in the debugfs
1809 tracing directory.
1810
1811 ftrace_graph_filter=[function-list]
1812 [FTRACE] Limit the top level callers functions traced
1813 by the function graph tracer at boot up.
1814 function-list is a comma-separated list of functions
1815 that can be changed at run time by the
1816 set_graph_function file in the debugfs tracing directory.
1817
1818 ftrace_graph_notrace=[function-list]
1819 [FTRACE] Do not trace from the functions specified in
1820 function-list. This list is a comma-separated list of
1821 functions that can be changed at run time by the
1822 set_graph_notrace file in the debugfs tracing directory.
1823
1824 ftrace_graph_max_depth=<uint>
1825 [FTRACE] Used with the function graph tracer. This is
1826 the max depth it will trace into a function. This value
1827 can be changed at run time by the max_graph_depth file
1828 in the tracefs tracing directory. default: 0 (no limit)
1829
1830 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier
1831 devices by scanning the firmware to infer the
1832 consumer/supplier relationships. This feature is
1833 especially useful when drivers are loaded as modules as
1834 it ensures proper ordering of tasks like device probing
1835 (suppliers first, then consumers), supplier boot state
1836 clean up (only after all consumers have probed),
1837 suspend/resume & runtime PM (consumers first, then
1838 suppliers).
1839 Format: { off | permissive | on | rpm }
1840 off -- Don't create device links from firmware info.
1841 permissive -- Create device links from firmware info
1842 but use it only for ordering boot state clean
1843 up (sync_state() calls).
1844 on -- Create device links from firmware info and use it
1845 to enforce probe and suspend/resume ordering.
1846 rpm -- Like "on", but also use to order runtime PM.
1847
1848 fw_devlink.strict=<bool>
1849 [KNL,EARLY] Treat all inferred dependencies as mandatory
1850 dependencies. This only applies for fw_devlink=on|rpm.
1851 Format: <bool>
1852
1853 fw_devlink.sync_state =
1854 [KNL,EARLY] When all devices that could probe have finished
1855 probing, this parameter controls what to do with
1856 devices that haven't yet received their sync_state()
1857 calls.
1858 Format: { strict | timeout }
1859 strict -- Default. Continue waiting on consumers to
1860 probe successfully.
1861 timeout -- Give up waiting on consumers and call
1862 sync_state() on any devices that haven't yet
1863 received their sync_state() calls after
1864 deferred_probe_timeout has expired or by
1865 late_initcall() if !CONFIG_MODULES.
1866
1867 gamecon.map[2|3]=
1868 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1869 support via parallel port (up to 5 devices per port)
1870 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1871 See also Documentation/input/devices/joystick-parport.rst
1872
1873 gamma= [HW,DRM]
1874
1875 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART
1876 Format: off | on
1877 default: on
1878
1879 gather_data_sampling=
1880 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS)
1881 mitigation.
1882
1883 Gather Data Sampling is a hardware vulnerability which
1884 allows unprivileged speculative access to data which was
1885 previously stored in vector registers.
1886
1887 This issue is mitigated by default in updated microcode.
1888 The mitigation may have a performance impact but can be
1889 disabled. On systems without the microcode mitigation
1890 disabling AVX serves as a mitigation.
1891
1892 force: Disable AVX to mitigate systems without
1893 microcode mitigation. No effect if the microcode
1894 mitigation is present. Known to cause crashes in
1895 userspace with buggy AVX enumeration.
1896
1897 off: Disable GDS mitigation.
1898
1899 gbpages [X86] Use GB pages for kernel direct mappings.
1900
1901 gcov_persist= [GCOV] When non-zero (default), profiling data for
1902 kernel modules is saved and remains accessible via
1903 debugfs, even when the module is unloaded/reloaded.
1904 When zero, profiling data is discarded and associated
1905 debugfs files are removed at module unload time.
1906
1907 goldfish [X86] Enable the goldfish android emulator platform.
1908 Don't use this when you are not running on the
1909 android emulator
1910
1911 gpio-mockup.gpio_mockup_ranges
1912 [HW] Sets the ranges of gpiochip of for this device.
1913 Format: <start1>,<end1>,<start2>,<end2>...
1914 gpio-mockup.gpio_mockup_named_lines
1915 [HW] Let the driver know GPIO lines should be named.
1916
1917 gpt [EFI] Forces disk with valid GPT signature but
1918 invalid Protective MBR to be treated as GPT. If the
1919 primary GPT is corrupted, it enables the backup/alternate
1920 GPT to be used instead.
1921
1922 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1923 the "Enable 0" bit of the configuration register.
1924 Format: 0 | 1
1925 Default: 0
1926 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1927 the "Enable 0" bit of the configuration register.
1928 Format: 0 | 1
1929 Default: 0
1930 grcan.select= [HW] Select which physical interface to use.
1931 Format: 0 | 1
1932 Default: 0
1933 grcan.txsize= [HW] Sets the size of the tx buffer.
1934 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1935 Default: 1024
1936 grcan.rxsize= [HW] Sets the size of the rx buffer.
1937 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1938 Default: 1024
1939
1940 hardened_usercopy=
1941 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1942 hardening is enabled for this boot. Hardened
1943 usercopy checking is used to protect the kernel
1944 from reading or writing beyond known memory
1945 allocation boundaries as a proactive defense
1946 against bounds-checking flaws in the kernel's
1947 copy_to_user()/copy_from_user() interface.
1948 The default is determined by
1949 CONFIG_HARDENED_USERCOPY_DEFAULT_ON.
1950 on Perform hardened usercopy checks.
1951 off Disable hardened usercopy checks.
1952
1953 hardlockup_all_cpu_backtrace=
1954 [KNL] Should the hard-lockup detector generate
1955 backtraces on all cpus.
1956 Format: 0 | 1
1957
1958 hash_pointers=
1959 [KNL,EARLY]
1960 By default, when pointers are printed to the console
1961 or buffers via the %p format string, that pointer is
1962 "hashed", i.e. obscured by hashing the pointer value.
1963 This is a security feature that hides actual kernel
1964 addresses from unprivileged users, but it also makes
1965 debugging the kernel more difficult since unequal
1966 pointers can no longer be compared. The choices are:
1967 Format: { auto | always | never }
1968 Default: auto
1969
1970 auto - Hash pointers unless slab_debug is enabled.
1971 always - Always hash pointers (even if slab_debug is
1972 enabled).
1973 never - Never hash pointers. This option should only
1974 be specified when debugging the kernel. Do
1975 not use on production kernels. The boot
1976 param "no_hash_pointers" is an alias for
1977 this mode.
1978
1979 For controlling hashing dynamically at runtime,
1980 use the "kernel.kptr_restrict" sysctl instead.
1981
1982 hashdist= [KNL,NUMA] Large hashes allocated during boot
1983 are distributed across NUMA nodes. Defaults on
1984 for 64-bit NUMA, off otherwise.
1985 Format: 0 | 1 (for off | on)
1986
1987 hd= [EIDE] (E)IDE hard drive subsystem geometry
1988 Format: <cyl>,<head>,<sect>
1989
1990 hest_disable [ACPI]
1991 Disable Hardware Error Source Table (HEST) support;
1992 corresponding firmware-first mode error processing
1993 logic will be disabled.
1994
1995 hibernate= [HIBERNATION]
1996 noresume Don't check if there's a hibernation image
1997 present during boot.
1998 nocompress Don't compress/decompress hibernation images.
1999 no Disable hibernation and resume.
2000 protect_image Turn on image protection during restoration
2001 (that will set all pages holding image data
2002 during restoration read-only).
2003
2004 hibernate.compressor= [HIBERNATION] Compression algorithm to be
2005 used with hibernation.
2006 Format: { lzo | lz4 }
2007 Default: lzo
2008
2009 lzo: Select LZO compression algorithm to
2010 compress/decompress hibernation image.
2011
2012 lz4: Select LZ4 compression algorithm to
2013 compress/decompress hibernation image.
2014
2015 hibernate.pm_test_delay=
2016 [HIBERNATION]
2017 Sets the number of seconds to remain in a hibernation test
2018 mode before resuming the system (see
2019 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
2020 is set. Default value is 5.
2021
2022 hibernate_compression_threads=
2023 [HIBERNATION]
2024 Set the number of threads used for compressing or decompressing
2025 hibernation images.
2026
2027 Format: <integer>
2028 Default: 3
2029 Minimum: 1
2030 Example: hibernate_compression_threads=4
2031
2032 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact
2033 size of <nn>. This works even on boxes that have no
2034 highmem otherwise. This also works to reduce highmem
2035 size on bigger boxes.
2036
2037 highres= [KNL] Enable/disable high resolution timer mode.
2038 Valid parameters: "on", "off"
2039 Default: "on"
2040
2041 hlt [BUGS=ARM,SH]
2042
2043 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename).
2044 Format: <string>
2045 This allows setting the system's hostname during early
2046 startup. This sets the name returned by gethostname.
2047 Using this parameter to set the hostname makes it
2048 possible to ensure the hostname is correctly set before
2049 any userspace processes run, avoiding the possibility
2050 that a process may call gethostname before the hostname
2051 has been explicitly set, resulting in the calling
2052 process getting an incorrect result. The string must
2053 not exceed the maximum allowed hostname length (usually
2054 64 characters) and will be truncated otherwise.
2055
2056 hpet= [X86-32,HPET] option to control HPET usage
2057 Format: { enable (default) | disable | force |
2058 verbose }
2059 disable: disable HPET and use PIT instead
2060 force: allow force enabled of undocumented chips (ICH4,
2061 VIA, nVidia)
2062 verbose: show contents of HPET registers during setup
2063
2064 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
2065 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
2066
2067 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot.
2068 If this follows hugepagesz (below), it specifies
2069 the number of pages of hugepagesz to be allocated.
2070 If this is the first HugeTLB parameter on the command
2071 line, it specifies the number of pages to allocate for
2072 the default huge page size. If using node format, the
2073 number of pages to allocate per-node can be specified.
2074 See also Documentation/admin-guide/mm/hugetlbpage.rst.
2075 Format: <integer> or (node format)
2076 <node>:<integer>[,<node>:<integer>]
2077
2078 hugepagesz=
2079 [HW,EARLY] The size of the HugeTLB pages. This is
2080 used in conjunction with hugepages (above) to
2081 allocate huge pages of a specific size at boot. The
2082 pair hugepagesz=X hugepages=Y can be specified once
2083 for each supported huge page size. Huge page sizes
2084 are architecture dependent. See also
2085 Documentation/admin-guide/mm/hugetlbpage.rst.
2086 Format: size[KMG]
2087
2088 hugepage_alloc_threads=
2089 [HW] The number of threads that should be used to
2090 allocate hugepages during boot. This option can be
2091 used to improve system bootup time when allocating
2092 a large amount of huge pages.
2093 The default value is 25% of the available hardware threads.
2094
2095 Note that this parameter only applies to non-gigantic huge pages.
2096
2097 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation
2098 of gigantic hugepages. Or using node format, the size
2099 of a CMA area per node can be specified.
2100 Format: nn[KMGTPE] or (node format)
2101 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
2102
2103 Reserve a CMA area of given size and allocate gigantic
2104 hugepages using the CMA allocator. If enabled, the
2105 boot-time allocation of gigantic hugepages is skipped.
2106
2107 hugetlb_cma_only=
2108 [HW,CMA,EARLY] When allocating new HugeTLB pages, only
2109 try to allocate from the CMA areas.
2110
2111 This option does nothing if hugetlb_cma= is not also
2112 specified.
2113
2114 hugetlb_free_vmemmap=
2115 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
2116 enabled.
2117 Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
2118 Allows heavy hugetlb users to free up some more
2119 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
2120 Format: { on | off (default) }
2121
2122 on: enable HVO
2123 off: disable HVO
2124
2125 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
2126 the default is on.
2127
2128 Note that the vmemmap pages may be allocated from the added
2129 memory block itself when memory_hotplug.memmap_on_memory is
2130 enabled, those vmemmap pages cannot be optimized even if this
2131 feature is enabled. Other vmemmap pages not allocated from
2132 the added memory block itself do not be affected.
2133
2134 hung_task_panic=
2135 [KNL] Number of hung tasks to trigger kernel panic.
2136 Format: <int>
2137
2138 When set to a non-zero value, a kernel panic will be triggered if
2139 the number of detected hung tasks reaches this value.
2140
2141 0: don't panic
2142 1: panic immediately on first hung task
2143 N: panic after N hung tasks are detected in a single scan
2144
2145 The default value is controlled by the
2146 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value
2147 selected by this boot parameter can be changed later by the
2148 kernel.hung_task_panic sysctl.
2149
2150 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
2151 terminal devices. Valid values: 0..8
2152 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
2153 If specified, z/VM IUCV HVC accepts connections
2154 from listed z/VM user IDs only.
2155
2156 hv_nopvspin [X86,HYPER_V,EARLY]
2157 Disables the paravirt spinlock optimizations
2158 which allow the hypervisor to 'idle' the guest
2159 on lock contention.
2160
2161 hw_protection= [HW]
2162 Format: reboot | shutdown
2163
2164 Hardware protection action taken on critical events like
2165 overtemperature or imminent voltage loss.
2166
2167 i2c_bus= [HW] Override the default board specific I2C bus speed
2168 or register an additional I2C bus that is not
2169 registered from board initialization code.
2170 Format:
2171 <bus_id>,<clkrate>
2172
2173 i2c_touchscreen_props= [HW,ACPI,X86]
2174 Set device-properties for ACPI-enumerated I2C-attached
2175 touchscreen, to e.g. fix coordinates of upside-down
2176 mounted touchscreens. If you need this option please
2177 submit a drivers/platform/x86/touchscreen_dmi.c patch
2178 adding a DMI quirk for this.
2179
2180 Format:
2181 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...]
2182 Where <val> is one of:
2183 Omit "=<val>" entirely Set a boolean device-property
2184 Unsigned number Set a u32 device-property
2185 Anything else Set a string device-property
2186
2187 Examples (split over multiple lines):
2188 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x:
2189 touchscreen-inverted-y
2190
2191 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920:
2192 touchscreen-size-y=1080:touchscreen-inverted-y:
2193 firmware-name=gsl1680-vendor-model.fw:silead,home-button
2194
2195 i8042.debug [HW] Toggle i8042 debug mode
2196 i8042.unmask_kbd_data
2197 [HW] Enable printing of interrupt data from the KBD port
2198 (disabled by default, and as a pre-condition
2199 requires that i8042.debug=1 be enabled)
2200 i8042.direct [HW] Put keyboard port into non-translated mode
2201 i8042.dumbkbd [HW] Pretend that controller can only read data from
2202 keyboard and cannot control its state
2203 (Don't attempt to blink the leds)
2204 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
2205 i8042.nokbd [HW] Don't check/create keyboard port
2206 i8042.noloop [HW] Disable the AUX Loopback command while probing
2207 for the AUX port
2208 i8042.nomux [HW] Don't check presence of an active multiplexing
2209 controller
2210 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
2211 controllers
2212 i8042.notimeout [HW] Ignore timeout condition signalled by controller
2213 i8042.reset [HW] Reset the controller during init, cleanup and
2214 suspend-to-ram transitions, only during s2r
2215 transitions, or never reset
2216 Format: { 1 | Y | y | 0 | N | n }
2217 1, Y, y: always reset controller
2218 0, N, n: don't ever reset controller
2219 Default: only on s2r transitions on x86; most other
2220 architectures force reset to be always executed
2221 i8042.unlock [HW] Unlock (ignore) the keylock
2222 i8042.kbdreset [HW] Reset device connected to KBD port
2223 i8042.probe_defer
2224 [HW] Allow deferred probing upon i8042 probe errors
2225
2226 i810= [HW,DRM]
2227
2228 i915.invert_brightness=
2229 [DRM] Invert the sense of the variable that is used to
2230 set the brightness of the panel backlight. Normally a
2231 brightness value of 0 indicates backlight switched off,
2232 and the maximum of the brightness value sets the backlight
2233 to maximum brightness. If this parameter is set to 0
2234 (default) and the machine requires it, or this parameter
2235 is set to 1, a brightness value of 0 sets the backlight
2236 to maximum brightness, and the maximum of the brightness
2237 value switches the backlight off.
2238 -1 -- never invert brightness
2239 0 -- machine default
2240 1 -- force brightness inversion
2241
2242 ia32_emulation= [X86-64]
2243 Format: <bool>
2244 When true, allows loading 32-bit programs and executing 32-bit
2245 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at
2246 boot time. When false, unconditionally disables IA32 emulation.
2247
2248 icn= [HW,ISDN]
2249 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
2250
2251
2252 idle= [X86,EARLY]
2253 Format: idle=poll, idle=halt, idle=nomwait
2254
2255 idle=poll: Don't do power saving in the idle loop
2256 using HLT, but poll for rescheduling event. This will
2257 make the CPUs eat a lot more power, but may be useful
2258 to get slightly better performance in multiprocessor
2259 benchmarks. It also makes some profiling using
2260 performance counters more accurate. Please note that
2261 on systems with MONITOR/MWAIT support (like Intel
2262 EM64T CPUs) this option has no performance advantage
2263 over the normal idle loop. It may also interact badly
2264 with hyperthreading.
2265
2266 idle=halt: Halt is forced to be used for CPU idle.
2267 In such case C2/C3 won't be used again.
2268
2269 idle=nomwait: Disable mwait for CPU C-states
2270
2271 idxd.sva= [HW]
2272 Format: <bool>
2273 Allow force disabling of Shared Virtual Memory (SVA)
2274 support for the idxd driver. By default it is set to
2275 true (1).
2276
2277 idxd.tc_override= [HW]
2278 Format: <bool>
2279 Allow override of default traffic class configuration
2280 for the device. By default it is set to false (0).
2281
2282 ieee754= [MIPS] Select IEEE Std 754 conformance mode
2283 Format: { strict | legacy | 2008 | relaxed | emulated }
2284 Default: strict
2285
2286 Choose which programs will be accepted for execution
2287 based on the IEEE 754 NaN encoding(s) supported by
2288 the FPU and the NaN encoding requested with the value
2289 of an ELF file header flag individually set by each
2290 binary. Hardware implementations are permitted to
2291 support either or both of the legacy and the 2008 NaN
2292 encoding mode.
2293
2294 Available settings are as follows:
2295 strict accept binaries that request a NaN encoding
2296 supported by the FPU
2297 legacy only accept legacy-NaN binaries, if supported
2298 by the FPU
2299 2008 only accept 2008-NaN binaries, if supported
2300 by the FPU
2301 relaxed accept any binaries regardless of whether
2302 supported by the FPU
2303 emulated accept any binaries but enable FPU emulator
2304 if binary mode is unsupported by the FPU.
2305
2306 The FPU emulator is always able to support both NaN
2307 encodings, so if no FPU hardware is present or it has
2308 been disabled with 'nofpu', then the settings of
2309 'legacy' and '2008' strap the emulator accordingly,
2310 'relaxed' straps the emulator for both legacy-NaN and
2311 2008-NaN, whereas 'strict' enables legacy-NaN only on
2312 legacy processors and both NaN encodings on MIPS32 or
2313 MIPS64 CPUs.
2314
2315 The setting for ABS.fmt/NEG.fmt instruction execution
2316 mode generally follows that for the NaN encoding,
2317 except where unsupported by hardware.
2318
2319 ignore_loglevel [KNL,EARLY]
2320 Ignore loglevel setting - this will print /all/
2321 kernel messages to the console. Useful for debugging.
2322 We also add it as printk module parameter, so users
2323 could change it dynamically, usually by
2324 /sys/module/printk/parameters/ignore_loglevel.
2325
2326 ignore_rlimit_data
2327 Ignore RLIMIT_DATA setting for data mappings,
2328 print warning at first misuse. Can be changed via
2329 /sys/module/kernel/parameters/ignore_rlimit_data.
2330
2331 ihash_entries= [KNL]
2332 Set number of hash buckets for inode cache.
2333
2334 ima_appraise= [IMA] appraise integrity measurements
2335 Format: { "off" | "enforce" | "fix" | "log" }
2336 default: "enforce"
2337
2338 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
2339 The builtin appraise policy appraises all files
2340 owned by uid=0.
2341
2342 ima_canonical_fmt [IMA]
2343 Use the canonical format for the binary runtime
2344 measurements, instead of host native format.
2345
2346 ima_hash= [IMA]
2347 Format: { md5 | sha1 | rmd160 | sha256 | sha384
2348 | sha512 | ... }
2349 default: "sha1"
2350
2351 The list of supported hash algorithms is defined
2352 in crypto/hash_info.h.
2353
2354 ima_policy= [IMA]
2355 The builtin policies to load during IMA setup.
2356 Format: "tcb | appraise_tcb | secure_boot |
2357 fail_securely | critical_data"
2358
2359 The "tcb" policy measures all programs exec'd, files
2360 mmap'd for exec, and all files opened with the read
2361 mode bit set by either the effective uid (euid=0) or
2362 uid=0.
2363
2364 The "appraise_tcb" policy appraises the integrity of
2365 all files owned by root.
2366
2367 The "secure_boot" policy appraises the integrity
2368 of files (eg. kexec kernel image, kernel modules,
2369 firmware, policy, etc) based on file signatures.
2370
2371 The "fail_securely" policy forces file signature
2372 verification failure also on privileged mounted
2373 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
2374 flag.
2375
2376 The "critical_data" policy measures kernel integrity
2377 critical data.
2378
2379 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
2380 Load a policy which meets the needs of the Trusted
2381 Computing Base. This means IMA will measure all
2382 programs exec'd, files mmap'd for exec, and all files
2383 opened for read by uid=0.
2384
2385 ima_template= [IMA]
2386 Select one of defined IMA measurements template formats.
2387 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
2388 "ima-sigv2" }
2389 Default: "ima-ng"
2390
2391 ima_template_fmt=
2392 [IMA] Define a custom template format.
2393 Format: { "field1|...|fieldN" }
2394
2395 ima= [IMA] Enable or disable IMA
2396 Format: { "off" | "on" }
2397 Default: "on"
2398 Note that disabling IMA is limited to kdump kernel.
2399
2400 indirect_target_selection= [X86,Intel] Mitigation control for Indirect
2401 Target Selection(ITS) bug in Intel CPUs. Updated
2402 microcode is also required for a fix in IBPB.
2403
2404 on: Enable mitigation (default).
2405 off: Disable mitigation.
2406 force: Force the ITS bug and deploy default
2407 mitigation.
2408 vmexit: Only deploy mitigation if CPU is affected by
2409 guest/host isolation part of ITS.
2410 stuff: Deploy RSB-fill mitigation when retpoline is
2411 also deployed. Otherwise, deploy the default
2412 mitigation.
2413
2414 For details see:
2415 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst
2416
2417 init= [KNL]
2418 Format: <full_path>
2419 Run specified binary instead of /sbin/init as init
2420 process.
2421
2422 initcall_debug [KNL] Trace initcalls as they are executed. Useful
2423 for working out where the kernel is dying during
2424 startup.
2425
2426 initcall_blacklist= [KNL] Do not execute a comma-separated list of
2427 initcall functions. Useful for debugging built-in
2428 modules and initcalls.
2429
2430 initramfs_async= [KNL]
2431 Format: <bool>
2432 Default: 1
2433 This parameter controls whether the initramfs
2434 image is unpacked asynchronously, concurrently
2435 with devices being probed and
2436 initialized. This should normally just work,
2437 but as a debugging aid, one can get the
2438 historical behaviour of the initramfs
2439 unpacking being completed before device_ and
2440 late_ initcalls.
2441
2442 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk
2443
2444 initrdmem= [KNL,EARLY] Specify a physical address and size from which to
2445 load the initrd. If an initrd is compiled in or
2446 specified in the bootparams, it takes priority over this
2447 setting.
2448 Format: ss[KMG],nn[KMG]
2449 Default is 0, 0
2450
2451 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with
2452 zeroes.
2453 Format: 0 | 1
2454 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2455
2456 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes.
2457 Format: 0 | 1
2458 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2459
2460 init_pkru= [X86] Specify the default memory protection keys rights
2461 register contents for all processes. 0x55555554 by
2462 default (disallow access to all but pkey 0). Can
2463 override in debugfs after boot.
2464
2465 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2466 Format: <irq>
2467
2468 int_pln_enable [X86] Enable power limit notification interrupt
2469
2470 integrity_audit=[IMA]
2471 Format: { "0" | "1" }
2472 0 -- basic integrity auditing messages. (Default)
2473 1 -- additional integrity auditing messages.
2474
2475 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2476 on
2477 Enable intel iommu driver.
2478 off
2479 Disable intel iommu driver.
2480 igfx_off [Default Off]
2481 By default, gfx is mapped as normal device. If a gfx
2482 device has a dedicated DMAR unit, the DMAR unit is
2483 bypassed by not enabling DMAR with this option. In
2484 this case, gfx device will use physical address for
2485 DMA.
2486 strict [Default Off]
2487 Deprecated, equivalent to iommu.strict=1.
2488 sp_off [Default Off]
2489 By default, super page will be supported if Intel IOMMU
2490 has the capability. With this option, super page will
2491 not be supported.
2492 sm_on
2493 Enable the Intel IOMMU scalable mode if the hardware
2494 advertises that it has support for the scalable mode
2495 translation.
2496 sm_off
2497 Disallow use of the Intel IOMMU scalable mode.
2498 tboot_noforce [Default Off]
2499 Do not force the Intel IOMMU enabled under tboot.
2500 By default, tboot will force Intel IOMMU on, which
2501 could harm performance of some high-throughput
2502 devices like 40GBit network cards, even if identity
2503 mapping is enabled.
2504 Note that using this option lowers the security
2505 provided by tboot because it makes the system
2506 vulnerable to DMA attacks.
2507
2508 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2509 0 disables intel_idle and fall back on acpi_idle.
2510 1 to 9 specify maximum depth of C-state.
2511
2512 intel_pstate= [X86,EARLY]
2513 disable
2514 Do not enable intel_pstate as the default
2515 scaling driver for the supported processors
2516 active
2517 Use intel_pstate driver to bypass the scaling
2518 governors layer of cpufreq and provides it own
2519 algorithms for p-state selection. There are two
2520 P-state selection algorithms provided by
2521 intel_pstate in the active mode: powersave and
2522 performance. The way they both operate depends
2523 on whether or not the hardware managed P-states
2524 (HWP) feature has been enabled in the processor
2525 and possibly on the processor model.
2526 passive
2527 Use intel_pstate as a scaling driver, but configure it
2528 to work with generic cpufreq governors (instead of
2529 enabling its internal governor). This mode cannot be
2530 used along with the hardware-managed P-states (HWP)
2531 feature.
2532 force
2533 Enable intel_pstate on systems that prohibit it by default
2534 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2535 instead of acpi-cpufreq may disable platform features, such
2536 as thermal controls and power capping, that rely on ACPI
2537 P-States information being indicated to OSPM and therefore
2538 should be used with caution. This option does not work with
2539 processors that aren't supported by the intel_pstate driver
2540 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2541 no_hwp
2542 Do not enable hardware P state control (HWP)
2543 if available.
2544 hwp_only
2545 Only load intel_pstate on systems which support
2546 hardware P state control (HWP) if available.
2547 support_acpi_ppc
2548 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2549 Description Table, specifies preferred power management
2550 profile as "Enterprise Server" or "Performance Server",
2551 then this feature is turned on by default.
2552 per_cpu_perf_limits
2553 Allow per-logical-CPU P-State performance control limits using
2554 cpufreq sysfs interface
2555 no_cas
2556 Do not enable capacity-aware scheduling (CAS) on
2557 hybrid systems
2558
2559 intremap= [X86-64,Intel-IOMMU,EARLY]
2560 on enable Interrupt Remapping (default)
2561 off disable Interrupt Remapping
2562 nosid disable Source ID checking
2563 no_x2apic_optout
2564 BIOS x2APIC opt-out request will be ignored
2565 nopost disable Interrupt Posting
2566 posted_msi
2567 enable MSIs delivered as posted interrupts
2568
2569 iomem= Disable strict checking of access to MMIO memory
2570 strict regions from userspace.
2571 relaxed
2572
2573 iommu= [X86,EARLY]
2574
2575 off
2576 Don't initialize and use any kind of IOMMU.
2577
2578 force
2579 Force the use of the hardware IOMMU even when
2580 it is not actually needed (e.g. because < 3 GB
2581 memory).
2582
2583 noforce
2584 Don't force hardware IOMMU usage when it is not
2585 needed. (default).
2586
2587 biomerge
2588 panic
2589 nopanic
2590 merge
2591 nomerge
2592
2593 soft
2594 Use software bounce buffering (SWIOTLB) (default for
2595 Intel machines). This can be used to prevent the usage
2596 of an available hardware IOMMU.
2597
2598 pt
2599 nopt
2600 nobypass [PPC/POWERNV]
2601 Disable IOMMU bypass, using IOMMU for PCI devices.
2602
2603 AMD Gart HW IOMMU-specific options:
2604
2605 <size>
2606 Set the size of the remapping area in bytes.
2607
2608 allowed
2609 Overwrite iommu off workarounds for specific chipsets
2610
2611 fullflush
2612 Flush IOMMU on each allocation (default).
2613
2614 nofullflush
2615 Don't use IOMMU fullflush.
2616
2617 memaper[=<order>]
2618 Allocate an own aperture over RAM with size
2619 32MB<<order. (default: order=1, i.e. 64MB)
2620
2621 merge
2622 Do scatter-gather (SG) merging. Implies "force"
2623 (experimental).
2624
2625 nomerge
2626 Don't do scatter-gather (SG) merging.
2627
2628 noaperture
2629 Ask the IOMMU not to touch the aperture for AGP.
2630
2631 noagp
2632 Don't initialize the AGP driver and use full aperture.
2633
2634 panic
2635 Always panic when IOMMU overflows.
2636
2637 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices.
2638 Format: { "0" | "1" }
2639 0 - Try to allocate a 32-bit DMA address first, before
2640 falling back to the full range if needed.
2641 1 - Allocate directly from the full usable range,
2642 forcing Dual Address Cycle for PCI cards supporting
2643 greater than 32-bit addressing.
2644
2645 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour
2646 Format: { "0" | "1" }
2647 0 - Lazy mode.
2648 Request that DMA unmap operations use deferred
2649 invalidation of hardware TLBs, for increased
2650 throughput at the cost of reduced device isolation.
2651 Will fall back to strict mode if not supported by
2652 the relevant IOMMU driver.
2653 1 - Strict mode.
2654 DMA unmap operations invalidate IOMMU hardware TLBs
2655 synchronously.
2656 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2657 Note: on x86, strict mode specified via one of the
2658 legacy driver-specific options takes precedence.
2659
2660 iommu.passthrough=
2661 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default.
2662 Format: { "0" | "1" }
2663 0 - Use IOMMU translation for DMA.
2664 1 - Bypass the IOMMU for DMA.
2665 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2666
2667 iommu.debug_pagealloc=
2668 [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this
2669 parameter enables the feature at boot time. By default, it
2670 is disabled and the system behaves the same way as a kernel
2671 built without CONFIG_IOMMU_DEBUG_PAGEALLOC.
2672 Format: { "0" | "1" }
2673 0 - Sanitizer disabled.
2674 1 - Sanitizer enabled, expect runtime overhead.
2675
2676 io7= [HW] IO7 for Marvel-based Alpha systems
2677 See comment before marvel_specify_io7 in
2678 arch/alpha/kernel/core_marvel.c.
2679
2680 io_delay= [X86,EARLY] I/O delay method
2681 0x80
2682 Standard port 0x80 based delay
2683 0xed
2684 Alternate port 0xed based delay (needed on some systems)
2685 udelay
2686 Simple two microseconds delay
2687 none
2688 No delay
2689
2690 ip= [IP_PNP]
2691 See Documentation/admin-guide/nfs/nfsroot.rst.
2692
2693 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V
2694 IPC identifiers from 32,768 to 16,777,216.
2695
2696 ipe.enforce= [IPE]
2697 Format: <bool>
2698 Determine whether IPE starts in permissive (0) or
2699 enforce (1) mode. The default is enforce.
2700
2701 ipe.success_audit=
2702 [IPE]
2703 Format: <bool>
2704 Start IPE with success auditing enabled, emitting
2705 an audit event when a binary is allowed. The default
2706 is 0.
2707
2708 irqaffinity= [SMP] Set the default irq affinity mask
2709 The argument is a cpu list, as described above.
2710
2711 irqchip.gicv2_force_probe=
2712 [ARM,ARM64,EARLY]
2713 Format: <bool>
2714 Force the kernel to look for the second 4kB page
2715 of a GICv2 controller even if the memory range
2716 exposed by the device tree is too small.
2717
2718 irqchip.gicv3_nolpi=
2719 [ARM,ARM64,EARLY]
2720 Force the kernel to ignore the availability of
2721 LPIs (and by consequence ITSs). Intended for system
2722 that use the kernel as a bootloader, and thus want
2723 to let secondary kernels in charge of setting up
2724 LPIs.
2725
2726 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY]
2727 Enables support for pseudo-NMIs in the kernel. This
2728 requires the kernel to be built with
2729 CONFIG_ARM64_PSEUDO_NMI.
2730
2731 irqchip.riscv_imsic_noipi
2732 [RISC-V,EARLY]
2733 Force the kernel to not use IMSIC software injected MSIs
2734 as IPIs. Intended for system where IMSIC is trap-n-emulated,
2735 and thus want to reduce MMIO traps when triggering IPIs
2736 to multiple harts.
2737
2738 irqfixup [HW]
2739 When an interrupt is not handled search all handlers
2740 for it. Intended to get systems with badly broken
2741 firmware running.
2742
2743 irqhandler.duration_warn_us= [KNL]
2744 Warn if an IRQ handler exceeds the specified duration
2745 threshold in microseconds. Useful for identifying
2746 long-running IRQs in the system.
2747
2748 irqpoll [HW]
2749 When an interrupt is not handled search all handlers
2750 for it. Also check all handlers each timer
2751 interrupt. Intended to get systems with badly broken
2752 firmware running.
2753
2754 isapnp= [ISAPNP]
2755 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2756
2757 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2758 [Deprecated - use cpusets instead]
2759 Format: [flag-list,]<cpu-list>
2760
2761 Specify one or more CPUs to isolate from disturbances
2762 specified in the flag list (default: domain):
2763
2764 nohz
2765 Disable the tick when a single task runs as well as
2766 disabling other kernel noises like having RCU callbacks
2767 offloaded. This is equivalent to the nohz_full parameter.
2768
2769 A residual 1Hz tick is offloaded to workqueues, which you
2770 need to affine to housekeeping through the global
2771 workqueue's affinity configured via the
2772 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2773 by using the 'domain' flag described below.
2774
2775 NOTE: by default the global workqueue runs on all CPUs,
2776 so to protect individual CPUs the 'cpumask' file has to
2777 be configured manually after bootup.
2778
2779 domain
2780 Isolate from the general SMP balancing and scheduling
2781 algorithms. Note that performing domain isolation this way
2782 is irreversible: it's not possible to bring back a CPU to
2783 the domains once isolated through isolcpus. It's strongly
2784 advised to use cpusets instead to disable scheduler load
2785 balancing through the "cpuset.sched_load_balance" file.
2786 It offers a much more flexible interface where CPUs can
2787 move in and out of an isolated set anytime.
2788
2789 You can move a process onto or off an "isolated" CPU via
2790 the CPU affinity syscalls or cpuset.
2791 <cpu number> begins at 0 and the maximum value is
2792 "number of CPUs in system - 1".
2793
2794 managed_irq
2795
2796 Isolate from being targeted by managed interrupts
2797 which have an interrupt mask containing isolated
2798 CPUs. The affinity of managed interrupts is
2799 handled by the kernel and cannot be changed via
2800 the /proc/irq/* interfaces.
2801
2802 This isolation is best effort and only effective
2803 if the automatically assigned interrupt mask of a
2804 device queue contains isolated and housekeeping
2805 CPUs. If housekeeping CPUs are online then such
2806 interrupts are directed to the housekeeping CPU
2807 so that IO submitted on the housekeeping CPU
2808 cannot disturb the isolated CPU.
2809
2810 If a queue's affinity mask contains only isolated
2811 CPUs then this parameter has no effect on the
2812 interrupt routing decision, though interrupts are
2813 only delivered when tasks running on those
2814 isolated CPUs submit IO. IO submitted on
2815 housekeeping CPUs has no influence on those
2816 queues.
2817
2818 The format of <cpu-list> is described above.
2819
2820 iucv= [HW,NET]
2821
2822 ivrs_ioapic [HW,X86-64]
2823 Provide an override to the IOAPIC-ID<->DEVICE-ID
2824 mapping provided in the IVRS ACPI table.
2825 By default, PCI segment is 0, and can be omitted.
2826
2827 For example, to map IOAPIC-ID decimal 10 to
2828 PCI segment 0x1 and PCI device 00:14.0,
2829 write the parameter as:
2830 ivrs_ioapic=10@0001:00:14.0
2831
2832 Deprecated formats:
2833 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0
2834 write the parameter as:
2835 ivrs_ioapic[10]=00:14.0
2836 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and
2837 PCI device 00:14.0 write the parameter as:
2838 ivrs_ioapic[10]=0001:00:14.0
2839
2840 ivrs_hpet [HW,X86-64]
2841 Provide an override to the HPET-ID<->DEVICE-ID
2842 mapping provided in the IVRS ACPI table.
2843 By default, PCI segment is 0, and can be omitted.
2844
2845 For example, to map HPET-ID decimal 10 to
2846 PCI segment 0x1 and PCI device 00:14.0,
2847 write the parameter as:
2848 ivrs_hpet=10@0001:00:14.0
2849
2850 Deprecated formats:
2851 * To map HPET-ID decimal 0 to PCI device 00:14.0
2852 write the parameter as:
2853 ivrs_hpet[0]=00:14.0
2854 * To map HPET-ID decimal 10 to PCI segment 0x1 and
2855 PCI device 00:14.0 write the parameter as:
2856 ivrs_ioapic[10]=0001:00:14.0
2857
2858 ivrs_acpihid [HW,X86-64]
2859 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2860 mapping provided in the IVRS ACPI table.
2861 By default, PCI segment is 0, and can be omitted.
2862
2863 For example, to map UART-HID:UID AMD0020:0 to
2864 PCI segment 0x1 and PCI device ID 00:14.5,
2865 write the parameter as:
2866 ivrs_acpihid=AMD0020:0@0001:00:14.5
2867
2868 Deprecated formats:
2869 * To map UART-HID:UID AMD0020:0 to PCI segment is 0,
2870 PCI device ID 00:14.5, write the parameter as:
2871 ivrs_acpihid[00:14.5]=AMD0020:0
2872 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and
2873 PCI device ID 00:14.5, write the parameter as:
2874 ivrs_acpihid[0001:00:14.5]=AMD0020:0
2875
2876 js= [HW,JOY] Analog joystick
2877 See Documentation/input/joydev/joystick.rst.
2878
2879 kasan_multi_shot
2880 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2881 report on every invalid memory access. Without this
2882 parameter KASAN will print report only for the first
2883 invalid access.
2884
2885 keep_bootcon [KNL,EARLY]
2886 Do not unregister boot console at start. This is only
2887 useful for debugging when something happens in the window
2888 between unregistering the boot console and initializing
2889 the real console.
2890
2891 keepinitrd [HW,ARM] See retain_initrd.
2892
2893 kernelcore= [KNL,X86,PPC,EARLY]
2894 Format: nn[KMGTPE] | nn% | "mirror"
2895 This parameter specifies the amount of memory usable by
2896 the kernel for non-movable allocations. The requested
2897 amount is spread evenly throughout all nodes in the
2898 system as ZONE_NORMAL. The remaining memory is used for
2899 movable memory in its own zone, ZONE_MOVABLE. In the
2900 event, a node is too small to have both ZONE_NORMAL and
2901 ZONE_MOVABLE, kernelcore memory will take priority and
2902 other nodes will have a larger ZONE_MOVABLE.
2903
2904 ZONE_MOVABLE is used for the allocation of pages that
2905 may be reclaimed or moved by the page migration
2906 subsystem. Note that allocations like PTEs-from-HighMem
2907 still use the HighMem zone if it exists, and the Normal
2908 zone if it does not.
2909
2910 It is possible to specify the exact amount of memory in
2911 the form of "nn[KMGTPE]", a percentage of total system
2912 memory in the form of "nn%", or "mirror". If "mirror"
2913 option is specified, mirrored (reliable) memory is used
2914 for non-movable allocations and remaining memory is used
2915 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2916 are exclusive, so you cannot specify multiple forms.
2917
2918 kfence.burst= [MM,KFENCE] The number of additional successive
2919 allocations to be attempted through KFENCE for each
2920 sample interval.
2921 Format: <unsigned integer>
2922 Default: 0
2923
2924 kfence.check_on_panic=
2925 [MM,KFENCE] Whether to check all KFENCE-managed objects'
2926 canaries on panic.
2927 Format: <bool>
2928 Default: false
2929
2930 kfence.deferrable=
2931 [MM,KFENCE] Whether to use a deferrable timer to trigger
2932 allocations. This avoids forcing CPU wake-ups if the
2933 system is idle, at the risk of a less predictable
2934 sample interval.
2935 Format: <bool>
2936 Default: CONFIG_KFENCE_DEFERRABLE
2937
2938 kfence.fault= [MM,KFENCE] Controls the behavior when a KFENCE
2939 error is detected.
2940 report - print the error report and continue (default).
2941 oops - print the error report and oops.
2942 panic - print the error report and panic.
2943
2944 kfence.sample_interval=
2945 [MM,KFENCE] KFENCE's sample interval in milliseconds.
2946 Format: <unsigned integer>
2947 0 - Disable KFENCE.
2948 >0 - Enabled KFENCE with given sample interval.
2949 Default: CONFIG_KFENCE_SAMPLE_INTERVAL
2950
2951 kfence.skip_covered_thresh=
2952 [MM,KFENCE] If pool utilization reaches this threshold
2953 (pool usage%), KFENCE limits currently covered
2954 allocations of the same source from further filling
2955 up the pool.
2956 Format: <unsigned integer>
2957 Default: 75
2958
2959 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port.
2960 Format: <Controller#>[,poll interval]
2961 The controller # is the number of the ehci usb debug
2962 port as it is probed via PCI. The poll interval is
2963 optional and is the number seconds in between
2964 each poll cycle to the debug port in case you need
2965 the functionality for interrupting the kernel with
2966 gdb or control-c on the dbgp connection. When
2967 not using this parameter you use sysrq-g to break into
2968 the kernel debugger.
2969
2970 kgdboc= [KGDB,HW] kgdb over consoles.
2971 Requires a tty driver that supports console polling,
2972 or a supported polling keyboard driver (non-usb).
2973 Serial only format: <serial_device>[,baud]
2974 keyboard only format: kbd
2975 keyboard and serial format: kbd,<serial_device>[,baud]
2976 Optional Kernel mode setting:
2977 kms, kbd format: kms,kbd
2978 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2979
2980 kgdboc_earlycon= [KGDB,HW,EARLY]
2981 If the boot console provides the ability to read
2982 characters and can work in polling mode, you can use
2983 this parameter to tell kgdb to use it as a backend
2984 until the normal console is registered. Intended to
2985 be used together with the kgdboc parameter which
2986 specifies the normal console to transition to.
2987
2988 The name of the early console should be specified
2989 as the value of this parameter. Note that the name of
2990 the early console might be different than the tty
2991 name passed to kgdboc. It's OK to leave the value
2992 blank and the first boot console that implements
2993 read() will be picked.
2994
2995 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the
2996 kernel debugger at the earliest opportunity.
2997
2998 kho= [KEXEC,EARLY]
2999 Format: { "0" | "1" | "off" | "on" | "y" | "n" }
3000 Enables or disables Kexec HandOver.
3001 "0" | "off" | "n" - kexec handover is disabled
3002 "1" | "on" | "y" - kexec handover is enabled
3003
3004 kho_scratch= [KEXEC,EARLY]
3005 Format: ll[KMG],mm[KMG],nn[KMG] | nn%
3006 Defines the size of the KHO scratch region. The KHO
3007 scratch regions are physically contiguous memory
3008 ranges that can only be used for non-kernel
3009 allocations. That way, even when memory is heavily
3010 fragmented with handed over memory, the kexeced
3011 kernel will always have enough contiguous ranges to
3012 bootstrap itself.
3013
3014 It is possible to specify the exact amount of
3015 memory in the form of "ll[KMG],mm[KMG],nn[KMG]"
3016 where the first parameter defines the size of a low
3017 memory scratch area, the second parameter defines
3018 the size of a global scratch area and the third
3019 parameter defines the size of additional per-node
3020 scratch areas. The form "nn%" defines scale factor
3021 (in percents) of memory that was used during boot.
3022
3023 kmac= [MIPS] Korina ethernet MAC address.
3024 Configure the RouterBoard 532 series on-chip
3025 Ethernet adapter MAC address.
3026
3027 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable
3028 Valid arguments: on, off
3029 Default: on
3030 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
3031 the default is off.
3032
3033 kprobe_event=[probe-list]
3034 [FTRACE] Add kprobe events and enable at boot time.
3035 The probe-list is a semicolon delimited list of probe
3036 definitions. Each definition is same as kprobe_events
3037 interface, but the parameters are comma delimited.
3038 For example, to add a kprobe event on vfs_read with
3039 arg1 and arg2, add to the command line;
3040
3041 kprobe_event=p,vfs_read,$arg1,$arg2
3042
3043 See also Documentation/trace/kprobetrace.rst "Kernel
3044 Boot Parameter" section.
3045
3046 kpti= [ARM64,EARLY] Control page table isolation of
3047 user and kernel address spaces.
3048 Default: enabled on cores which need mitigation.
3049 0: force disabled
3050 1: force enabled
3051
3052 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires
3053 CONFIG_KUNIT to be set to be fully enabled. The
3054 default value can be overridden via
3055 KUNIT_DEFAULT_ENABLED.
3056 Default is 1 (enabled)
3057
3058 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
3059 Default is 0 (don't ignore, but inject #GP)
3060
3061 kvm.eager_page_split=
3062 [KVM,X86] Controls whether or not KVM will try to
3063 proactively split all huge pages during dirty logging.
3064 Eager page splitting reduces interruptions to vCPU
3065 execution by eliminating the write-protection faults
3066 and MMU lock contention that would otherwise be
3067 required to split huge pages lazily.
3068
3069 VM workloads that rarely perform writes or that write
3070 only to a small region of VM memory may benefit from
3071 disabling eager page splitting to allow huge pages to
3072 still be used for reads.
3073
3074 The behavior of eager page splitting depends on whether
3075 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
3076 disabled, all huge pages in a memslot will be eagerly
3077 split when dirty logging is enabled on that memslot. If
3078 enabled, eager page splitting will be performed during
3079 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
3080 cleared.
3081
3082 Eager page splitting is only supported when kvm.tdp_mmu=Y.
3083
3084 Default is Y (on).
3085
3086 kvm.enable_pmu=[KVM,X86]
3087 If enabled, KVM will virtualize PMU functionality based
3088 on the virtual CPU model defined by userspace. This
3089 can be overridden on a per-VM basis via
3090 KVM_CAP_PMU_CAPABILITY.
3091
3092 If disabled, KVM will not virtualize PMU functionality,
3093 e.g. MSRs, PMCs, PMIs, etc., even if userspace defines
3094 a virtual CPU model that contains PMU assets.
3095
3096 Note, KVM's vPMU support implicitly requires running
3097 with an in-kernel local APIC, e.g. to deliver PMIs to
3098 the guest. Running without an in-kernel local APIC is
3099 not supported, though KVM will allow such a combination
3100 (with severely degraded functionality).
3101
3102 See also enable_mediated_pmu.
3103
3104 Default is Y (on).
3105
3106 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86]
3107 If enabled, KVM will enable virtualization in hardware
3108 when KVM is loaded, and disable virtualization when KVM
3109 is unloaded (if KVM is built as a module).
3110
3111 If disabled, KVM will dynamically enable and disable
3112 virtualization on-demand when creating and destroying
3113 VMs, i.e. on the 0=>1 and 1=>0 transitions of the
3114 number of VMs.
3115
3116 Enabling virtualization at module load avoids potential
3117 latency for creation of the 0=>1 VM, as KVM serializes
3118 virtualization enabling across all online CPUs. The
3119 "cost" of enabling virtualization when KVM is loaded,
3120 is that doing so may interfere with using out-of-tree
3121 hypervisors that want to "own" virtualization hardware.
3122
3123 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
3124 Default is false (don't support).
3125
3126 kvm.nx_huge_pages=
3127 [KVM] Controls the software workaround for the
3128 X86_BUG_ITLB_MULTIHIT bug.
3129 force : Always deploy workaround.
3130 off : Never deploy workaround.
3131 auto : Deploy workaround based on the presence of
3132 X86_BUG_ITLB_MULTIHIT.
3133
3134 Default is 'auto'.
3135
3136 If the software workaround is enabled for the host,
3137 guests do need not to enable it for nested guests.
3138
3139 kvm.nx_huge_pages_recovery_ratio=
3140 [KVM] Controls how many 4KiB pages are periodically zapped
3141 back to huge pages. 0 disables the recovery, otherwise if
3142 the value is N KVM will zap 1/Nth of the 4KiB pages every
3143 period (see below). The default is 60.
3144
3145 kvm.nx_huge_pages_recovery_period_ms=
3146 [KVM] Controls the time period at which KVM zaps 4KiB pages
3147 back to huge pages. If the value is a non-zero N, KVM will
3148 zap a portion (see ratio above) of the pages every N msecs.
3149 If the value is 0 (the default), KVM will pick a period based
3150 on the ratio, such that a page is zapped after 1 hour on average.
3151
3152 kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL]
3153 If enabled, KVM will provide a mediated virtual PMU,
3154 instead of the default perf-based virtual PMU (if
3155 kvm.enable_pmu is true and PMU is enumerated via the
3156 virtual CPU model).
3157
3158 With a perf-based vPMU, KVM operates as a user of perf,
3159 i.e. emulates guest PMU counters using perf events.
3160 KVM-created perf events are managed by perf as regular
3161 (guest-only) events, e.g. are scheduled in/out, contend
3162 for hardware resources, etc. Using a perf-based vPMU
3163 allows guest and host usage of the PMU to co-exist, but
3164 incurs non-trivial overhead and can result in silently
3165 dropped guest events (due to resource contention).
3166
3167 With a mediated vPMU, hardware PMU state is context
3168 switched around the world switch to/from the guest.
3169 KVM mediates which events the guest can utilize, but
3170 gives the guest direct access to all other PMU assets
3171 when possible (KVM may intercept some accesses if the
3172 virtual CPU model provides a subset of hardware PMU
3173 functionality). Using a mediated vPMU significantly
3174 reduces PMU virtualization overhead and eliminates lost
3175 guest events, but is mutually exclusive with using perf
3176 to profile KVM guests and adds latency to most VM-Exits
3177 (to context switch PMU state).
3178
3179 Default is N (off).
3180
3181 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in
3182 KVM/SVM. Default is 1 (enabled).
3183
3184 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,
3185 a.k.a. Two-Dimensional Page Tables. Default is 1
3186 (enabled). Disable by KVM if hardware lacks support
3187 for NPT.
3188
3189 kvm-amd.ciphertext_hiding_asids=
3190 [KVM,AMD] Ciphertext hiding prevents disallowed accesses
3191 to SNP private memory from reading ciphertext. Instead,
3192 reads will see constant default values (0xff).
3193
3194 If ciphertext hiding is enabled, the joint SEV-ES and
3195 SEV-SNP ASID space is partitioned into separate SEV-ES
3196 and SEV-SNP ASID ranges, with the SEV-SNP range being
3197 [1..max_snp_asid] and the SEV-ES range being
3198 (max_snp_asid..min_sev_asid), where min_sev_asid is
3199 enumerated by CPUID.0x.8000_001F[EDX].
3200
3201 A non-zero value enables SEV-SNP ciphertext hiding and
3202 adjusts the ASID ranges for SEV-ES and SEV-SNP guests.
3203 KVM caps the number of SEV-SNP ASIDs at the maximum
3204 possible value, e.g. specifying -1u will assign all
3205 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note,
3206 assigning all joint ASIDs to SEV-SNP, i.e. configuring
3207 max_snp_asid == min_sev_asid-1, will effectively make
3208 SEV-ES unusable.
3209
3210 kvm-arm.mode=
3211 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of
3212 operation.
3213
3214 none: Forcefully disable KVM.
3215
3216 nvhe: Standard nVHE-based mode, without support for
3217 protected guests.
3218
3219 protected: Mode with support for guests whose state is
3220 kept private from the host, using VHE or
3221 nVHE depending on HW support.
3222
3223 nested: VHE-based mode with support for nested
3224 virtualization. Requires at least ARMv8.4
3225 hardware (with FEAT_NV2).
3226
3227 Defaults to VHE/nVHE based on hardware support. Setting
3228 mode to "protected" will disable kexec and hibernation
3229 for the host. To force nVHE on VHE hardware, add
3230 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the
3231 command-line.
3232 "nested" and "protected" are experimental and should be
3233 used with extreme caution.
3234
3235 kvm-arm.vgic_v3_group0_trap=
3236 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0
3237 system registers
3238
3239 kvm-arm.vgic_v3_group1_trap=
3240 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1
3241 system registers
3242
3243 kvm-arm.vgic_v3_common_trap=
3244 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common
3245 system registers
3246
3247 kvm-arm.vgic_v4_enable=
3248 [KVM,ARM,EARLY] Allow use of GICv4 for direct
3249 injection of LPIs.
3250
3251 kvm-arm.wfe_trap_policy=
3252 [KVM,ARM] Control when to set WFE instruction trap for
3253 KVM VMs. Traps are allowed but not guaranteed by the
3254 CPU architecture.
3255
3256 trap: set WFE instruction trap
3257
3258 notrap: clear WFE instruction trap
3259
3260 kvm-arm.wfi_trap_policy=
3261 [KVM,ARM] Control when to set WFI instruction trap for
3262 KVM VMs. Traps are allowed but not guaranteed by the
3263 CPU architecture.
3264
3265 trap: set WFI instruction trap
3266
3267 notrap: clear WFI instruction trap
3268
3269 kvm_cma_resv_ratio=n [PPC,EARLY]
3270 Reserves given percentage from system memory area for
3271 contiguous memory allocation for KVM hash pagetable
3272 allocation.
3273 By default it reserves 5% of total system memory.
3274 Format: <integer>
3275 Default: 5
3276
3277 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
3278 a.k.a. Two-Dimensional Page Tables. Default is 1
3279 (enabled). Disable by KVM if hardware lacks support
3280 for EPT.
3281
3282 kvm-intel.emulate_invalid_guest_state=
3283 [KVM,Intel] Control whether to emulate invalid guest
3284 state. Ignored if kvm-intel.enable_unrestricted_guest=1,
3285 as guest state is never invalid for unrestricted
3286 guests. This param doesn't apply to nested guests (L2),
3287 as KVM never emulates invalid L2 guest state.
3288 Default is 1 (enabled).
3289
3290 kvm-intel.flexpriority=
3291 [KVM,Intel] Control KVM's use of FlexPriority feature
3292 (TPR shadow). Default is 1 (enabled). Disable by KVM if
3293 hardware lacks support for it.
3294
3295 kvm-intel.nested=
3296 [KVM,Intel] Control nested virtualization feature in
3297 KVM/VMX. Default is 1 (enabled).
3298
3299 kvm-intel.unrestricted_guest=
3300 [KVM,Intel] Control KVM's use of unrestricted guest
3301 feature (virtualized real and unpaged mode). Default
3302 is 1 (enabled). Disable by KVM if EPT is disabled or
3303 hardware lacks support for it.
3304
3305 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
3306 CVE-2018-3620.
3307
3308 Valid arguments: never, cond, always
3309
3310 always: L1D cache flush on every VMENTER.
3311 cond: Flush L1D on VMENTER only when the code between
3312 VMEXIT and VMENTER can leak host memory.
3313 never: Disables the mitigation
3314
3315 Default is cond (do L1 cache flush in specific instances)
3316
3317 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor
3318 Identification feature (tagged TLBs). Default is 1
3319 (enabled). Disable by KVM if hardware lacks support
3320 for it.
3321
3322 l1d_flush= [X86,INTEL,EARLY]
3323 Control mitigation for L1D based snooping vulnerability.
3324
3325 Certain CPUs are vulnerable to an exploit against CPU
3326 internal buffers which can forward information to a
3327 disclosure gadget under certain conditions.
3328
3329 In vulnerable processors, the speculatively
3330 forwarded data can be used in a cache side channel
3331 attack, to access data to which the attacker does
3332 not have direct access.
3333
3334 This parameter controls the mitigation. The
3335 options are:
3336
3337 on - enable the interface for the mitigation
3338
3339 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on
3340 affected CPUs
3341
3342 The kernel PTE inversion protection is unconditionally
3343 enabled and cannot be disabled.
3344
3345 full
3346 Provides all available mitigations for the
3347 L1TF vulnerability. Disables SMT and
3348 enables all mitigations in the
3349 hypervisors, i.e. unconditional L1D flush.
3350
3351 SMT control and L1D flush control via the
3352 sysfs interface is still possible after
3353 boot. Hypervisors will issue a warning
3354 when the first VM is started in a
3355 potentially insecure configuration,
3356 i.e. SMT enabled or L1D flush disabled.
3357
3358 full,force
3359 Same as 'full', but disables SMT and L1D
3360 flush runtime control. Implies the
3361 'nosmt=force' command line option.
3362 (i.e. sysfs control of SMT is disabled.)
3363
3364 flush
3365 Leaves SMT enabled and enables the default
3366 hypervisor mitigation, i.e. conditional
3367 L1D flush.
3368
3369 SMT control and L1D flush control via the
3370 sysfs interface is still possible after
3371 boot. Hypervisors will issue a warning
3372 when the first VM is started in a
3373 potentially insecure configuration,
3374 i.e. SMT enabled or L1D flush disabled.
3375
3376 flush,nosmt
3377
3378 Disables SMT and enables the default
3379 hypervisor mitigation.
3380
3381 SMT control and L1D flush control via the
3382 sysfs interface is still possible after
3383 boot. Hypervisors will issue a warning
3384 when the first VM is started in a
3385 potentially insecure configuration,
3386 i.e. SMT enabled or L1D flush disabled.
3387
3388 flush,nowarn
3389 Same as 'flush', but hypervisors will not
3390 warn when a VM is started in a potentially
3391 insecure configuration.
3392
3393 off
3394 Disables hypervisor mitigations and doesn't
3395 emit any warnings.
3396 It also drops the swap size and available
3397 RAM limit restriction on both hypervisor and
3398 bare metal.
3399
3400 Default is 'flush'.
3401
3402 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
3403
3404 l2cr= [PPC]
3405
3406 l3cr= [PPC]
3407
3408 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS
3409 disabled it.
3410
3411 lapic= [X86,APIC] Do not use TSC deadline
3412 value for LAPIC timer one-shot implementation. Default
3413 back to the programmable timer unit in the LAPIC.
3414 Format: notscdeadline
3415
3416 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer
3417 in C2 power state.
3418
3419 libata.dma= [LIBATA] DMA control
3420 libata.dma=0 Disable all PATA and SATA DMA
3421 libata.dma=1 PATA and SATA Disk DMA only
3422 libata.dma=2 ATAPI (CDROM) DMA only
3423 libata.dma=4 Compact Flash DMA only
3424 Combinations also work, so libata.dma=3 enables DMA
3425 for disks and CDROMs, but not CFs.
3426
3427 libata.ignore_hpa= [LIBATA] Ignore HPA limit
3428 libata.ignore_hpa=0 keep BIOS limits (default)
3429 libata.ignore_hpa=1 ignore limits, using full disk
3430
3431 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
3432 when set.
3433 Format: <int>
3434
3435 libata.force= [LIBATA] Force configurations. The format is a comma-
3436 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
3437 PORT and DEVICE are decimal numbers matching port, link
3438 or device. Basically, it matches the ATA ID string
3439 printed on console by libata. If the whole ID part is
3440 omitted, the last PORT and DEVICE values are used. If
3441 ID hasn't been specified yet, the configuration applies
3442 to all ports, links and devices.
3443
3444 If only DEVICE is omitted, the parameter applies to
3445 the port and all links and devices behind it. DEVICE
3446 number of 0 either selects the first device or the
3447 first fan-out link behind PMP device. It does not
3448 select the host link. DEVICE number of 15 selects the
3449 host link and device attached to it.
3450
3451 The VAL specifies the configuration to force. As long
3452 as there is no ambiguity, shortcut notation is allowed.
3453 For example, both 1.5 and 1.5G would work for 1.5Gbps.
3454 The following configurations can be forced.
3455
3456 * Cable type: 40c, 80c, short40c, unk, ign or sata.
3457 Any ID with matching PORT is used.
3458
3459 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
3460
3461 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
3462 udma[/][16,25,33,44,66,100,133] notation is also
3463 allowed.
3464
3465 * nohrst, nosrst, norst: suppress hard, soft and both
3466 resets.
3467
3468 * rstonce: only attempt one reset during hot-unplug
3469 link recovery.
3470
3471 * [no]dbdelay: Enable or disable the extra 200ms delay
3472 before debouncing a link PHY and device presence
3473 detection.
3474
3475 * [no]ncq: Turn on or off NCQ.
3476
3477 * [no]ncqtrim: Enable or disable queued DSM TRIM.
3478
3479 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
3480
3481 * [no]trim: Enable or disable (unqueued) TRIM.
3482
3483 * trim_zero: Indicate that TRIM command zeroes data.
3484
3485 * max_trim_128m: Set 128M maximum trim size limit.
3486
3487 * [no]dma: Turn on or off DMA transfers.
3488
3489 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
3490
3491 * atapi_mod16_dma: Enable the use of ATAPI DMA for
3492 commands that are not a multiple of 16 bytes.
3493
3494 * [no]dmalog: Enable or disable the use of the
3495 READ LOG DMA EXT command to access logs.
3496
3497 * [no]iddevlog: Enable or disable access to the
3498 identify device data log.
3499
3500 * [no]logdir: Enable or disable access to the general
3501 purpose log directory.
3502
3503 * max_sec=<sectors>: Set the transfer size limit, in
3504 number of 512-byte sectors, to the value specified in
3505 <sectors>. The value specified in <sectors> has to be
3506 a non-zero positive integer.
3507
3508 * max_sec_128: Set transfer size limit to 128 sectors.
3509
3510 * max_sec_1024: Set or clear transfer size limit to
3511 1024 sectors.
3512
3513 * max_sec_lba48: Set or clear transfer size limit to
3514 65535 sectors.
3515
3516 * external: Mark port as external (hotplug-capable).
3517
3518 * [no]lpm: Enable or disable link power management.
3519
3520 * [no]setxfer: Indicate if transfer speed mode setting
3521 should be skipped.
3522
3523 * [no]fua: Disable or enable FUA (Force Unit Access)
3524 support for devices supporting this feature.
3525
3526 * dump_id: Dump IDENTIFY data.
3527
3528 * disable: Disable this device.
3529
3530 If there are multiple matching configurations changing
3531 the same attribute, the last one is used.
3532
3533 liveupdate= [KNL,EARLY]
3534 Format: <bool>
3535 Enable Live Update Orchestrator (LUO).
3536 Default: off.
3537
3538 lockd.nlm_grace_period=P [NFS] Assign grace period.
3539 Format: <integer>
3540
3541 lockd.nlm_tcpport=N [NFS] Assign TCP port.
3542 Format: <integer>
3543
3544 lockd.nlm_timeout=T [NFS] Assign timeout value.
3545 Format: <integer>
3546
3547 lockd.nlm_udpport=M [NFS] Assign UDP port.
3548 Format: <integer>
3549
3550 lockdown= [SECURITY,EARLY]
3551 { integrity | confidentiality }
3552 Enable the kernel lockdown feature. If set to
3553 integrity, kernel features that allow userland to
3554 modify the running kernel are disabled. If set to
3555 confidentiality, kernel features that allow userland
3556 to extract confidential information from the kernel
3557 are also disabled.
3558
3559 locktorture.acq_writer_lim= [KNL]
3560 Set the time limit in jiffies for a lock
3561 acquisition. Acquisitions exceeding this limit
3562 will result in a splat once they do complete.
3563
3564 locktorture.bind_readers= [KNL]
3565 Specify the list of CPUs to which the readers are
3566 to be bound.
3567
3568 locktorture.bind_writers= [KNL]
3569 Specify the list of CPUs to which the writers are
3570 to be bound.
3571
3572 locktorture.call_rcu_chains= [KNL]
3573 Specify the number of self-propagating call_rcu()
3574 chains to set up. These are used to ensure that
3575 there is a high probability of an RCU grace period
3576 in progress at any given time. Defaults to 0,
3577 which disables these call_rcu() chains.
3578
3579 locktorture.long_hold= [KNL]
3580 Specify the duration in milliseconds for the
3581 occasional long-duration lock hold time. Defaults
3582 to 100 milliseconds. Select 0 to disable.
3583
3584 locktorture.nested_locks= [KNL]
3585 Specify the maximum lock nesting depth that
3586 locktorture is to exercise, up to a limit of 8
3587 (MAX_NESTED_LOCKS). Specify zero to disable.
3588 Note that this parameter is ineffective on types
3589 of locks that do not support nested acquisition.
3590
3591 locktorture.nreaders_stress= [KNL]
3592 Set the number of locking read-acquisition kthreads.
3593 Defaults to being automatically set based on the
3594 number of online CPUs.
3595
3596 locktorture.nwriters_stress= [KNL]
3597 Set the number of locking write-acquisition kthreads.
3598
3599 locktorture.onoff_holdoff= [KNL]
3600 Set time (s) after boot for CPU-hotplug testing.
3601
3602 locktorture.onoff_interval= [KNL]
3603 Set time (s) between CPU-hotplug operations, or
3604 zero to disable CPU-hotplug testing.
3605
3606 locktorture.rt_boost= [KNL]
3607 Do periodic testing of real-time lock priority
3608 boosting. Select 0 to disable, 1 to boost
3609 only rt_mutex, and 2 to boost unconditionally.
3610 Defaults to 2, which might seem to be an
3611 odd choice, but which should be harmless for
3612 non-real-time spinlocks, due to their disabling
3613 of preemption. Note that non-realtime mutexes
3614 disable boosting.
3615
3616 locktorture.rt_boost_factor= [KNL]
3617 Number that determines how often and for how
3618 long priority boosting is exercised. This is
3619 scaled down by the number of writers, so that the
3620 number of boosts per unit time remains roughly
3621 constant as the number of writers increases.
3622 On the other hand, the duration of each boost
3623 increases with the number of writers.
3624
3625 locktorture.shuffle_interval= [KNL]
3626 Set task-shuffle interval (jiffies). Shuffling
3627 tasks allows some CPUs to go into dyntick-idle
3628 mode during the locktorture test.
3629
3630 locktorture.shutdown_secs= [KNL]
3631 Set time (s) after boot system shutdown. This
3632 is useful for hands-off automated testing.
3633
3634 locktorture.stat_interval= [KNL]
3635 Time (s) between statistics printk()s.
3636
3637 locktorture.stutter= [KNL]
3638 Time (s) to stutter testing, for example,
3639 specifying five seconds causes the test to run for
3640 five seconds, wait for five seconds, and so on.
3641 This tests the locking primitive's ability to
3642 transition abruptly to and from idle.
3643
3644 locktorture.torture_type= [KNL]
3645 Specify the locking implementation to test.
3646
3647 locktorture.verbose= [KNL]
3648 Enable additional printk() statements.
3649
3650 locktorture.writer_fifo= [KNL]
3651 Run the write-side locktorture kthreads at
3652 sched_set_fifo() real-time priority.
3653
3654 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
3655 Format: <irq>
3656
3657 loglevel= [KNL,EARLY]
3658 All Kernel Messages with a loglevel smaller than the
3659 console loglevel will be printed to the console. It can
3660 also be changed with klogd or other programs. The
3661 loglevels are defined as follows:
3662
3663 0 (KERN_EMERG) system is unusable
3664 1 (KERN_ALERT) action must be taken immediately
3665 2 (KERN_CRIT) critical conditions
3666 3 (KERN_ERR) error conditions
3667 4 (KERN_WARNING) warning conditions
3668 5 (KERN_NOTICE) normal but significant condition
3669 6 (KERN_INFO) informational
3670 7 (KERN_DEBUG) debug-level messages
3671
3672 log_buf_len=n[KMG] [KNL,EARLY]
3673 Sets the size of the printk ring buffer, in bytes.
3674 n must be a power of two and greater than the
3675 minimal size. The minimal size is defined by
3676 LOG_BUF_SHIFT kernel config parameter. There
3677 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config
3678 parameter that allows to increase the default size
3679 depending on the number of CPUs. See init/Kconfig
3680 for more details.
3681
3682 logo.nologo [FB] Disables display of the built-in Linux logo.
3683 This may be used to provide more screen space for
3684 kernel log messages and is useful when debugging
3685 kernel boot problems.
3686
3687 lp=0 [LP] Specify parallel ports to use, e.g,
3688 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
3689 lp=reset first parallel port). 'lp=0' disables the
3690 lp=auto printer driver. 'lp=reset' (which can be
3691 specified in addition to the ports) causes
3692 attached printers to be reset. Using
3693 lp=port1,port2,... specifies the parallel ports
3694 to associate lp devices with, starting with
3695 lp0. A port specification may be 'none' to skip
3696 that lp device, or a parport name such as
3697 'parport0'. Specifying 'lp=auto' instead of a
3698 port specification list means that device IDs
3699 from each port should be examined, to see if
3700 an IEEE 1284-compliant printer is attached; if
3701 so, the driver will manage that printer.
3702 See also header of drivers/char/lp.c.
3703
3704 lpj=n [KNL]
3705 Sets loops_per_jiffy to given constant, thus avoiding
3706 time-consuming boot-time autodetection (up to 250 ms per
3707 CPU). 0 enables autodetection (default). To determine
3708 the correct value for your kernel, boot with normal
3709 autodetection and see what value is printed. Note that
3710 on SMP systems the preset will be applied to all CPUs,
3711 which is likely to cause problems if your CPUs need
3712 significantly divergent settings. An incorrect value
3713 will cause delays in the kernel to be wrong, leading to
3714 unpredictable I/O errors and other breakage. Although
3715 unlikely, in the extreme case this might damage your
3716 hardware.
3717
3718 lsm.debug [SECURITY] Enable LSM initialization debugging output.
3719
3720 lsm=lsm1,...,lsmN
3721 [SECURITY] Choose order of LSM initialization. This
3722 overrides CONFIG_LSM, and the "security=" parameter.
3723
3724 machtype= [Loongson] Share the same kernel image file between
3725 different yeeloong laptops.
3726 Example: machtype=lemote-yeeloong-2f-7inch
3727
3728 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
3729 will bring up during bootup. maxcpus=n : n >= 0 limits
3730 the kernel to bring up 'n' processors. Surely after
3731 bootup you can bring up the other plugged cpu by executing
3732 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
3733 only takes effect during system bootup.
3734 While n=0 is a special case, it is equivalent to "nosmp",
3735 which also disables the IO APIC.
3736
3737 max_loop= [LOOP] The number of loop block devices that get
3738 (loop.max_loop) unconditionally pre-created at init time. The default
3739 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
3740 of statically allocating a predefined number, loop
3741 devices can be requested on-demand with the
3742 /dev/loop-control interface.
3743
3744 mce= [X86-{32,64}]
3745
3746 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables.
3747
3748 off
3749 disable machine check
3750
3751 no_cmci
3752 disable CMCI(Corrected Machine Check Interrupt) that
3753 Intel processor supports. Usually this disablement is
3754 not recommended, but it might be handy if your
3755 hardware is misbehaving.
3756
3757 Note that you'll get more problems without CMCI than
3758 with due to the shared banks, i.e. you might get
3759 duplicated error logs.
3760
3761 dont_log_ce
3762 don't make logs for corrected errors. All events
3763 reported as corrected are silently cleared by OS. This
3764 option will be useful if you have no interest in any
3765 of corrected errors.
3766
3767 ignore_ce
3768 disable features for corrected errors, e.g.
3769 polling timer and CMCI. All events reported as
3770 corrected are not cleared by OS and remained in its
3771 error banks.
3772
3773 Usually this disablement is not recommended, however
3774 if there is an agent checking/clearing corrected
3775 errors (e.g. BIOS or hardware monitoring
3776 applications), conflicting with OS's error handling,
3777 and you cannot deactivate the agent, then this option
3778 will be a help.
3779
3780 no_lmce
3781 do not opt-in to Local MCE delivery. Use legacy method
3782 to broadcast MCEs.
3783
3784 bootlog
3785 enable logging of machine checks left over from
3786 booting. Disabled by default on AMD Fam10h and older
3787 because some BIOS leave bogus ones.
3788
3789 If your BIOS doesn't do that it's a good idea to
3790 enable though to make sure you log even machine check
3791 events that result in a reboot. On Intel systems it is
3792 enabled by default.
3793
3794 nobootlog
3795 disable boot machine check logging.
3796
3797 monarchtimeout (number)
3798 sets the time in us to wait for other CPUs on machine
3799 checks. 0 to disable.
3800
3801 bios_cmci_threshold
3802 don't overwrite the bios-set CMCI threshold. This boot
3803 option prevents Linux from overwriting the CMCI
3804 threshold set by the bios. Without this option, Linux
3805 always sets the CMCI threshold to 1. Enabling this may
3806 make memory predictive failure analysis less effective
3807 if the bios sets thresholds for memory errors since we
3808 will not see details for all errors.
3809
3810 recovery
3811 force-enable recoverable machine check code paths
3812
3813 Everything else is in sysfs now.
3814
3815
3816 md= [HW] RAID subsystems devices and level
3817 See Documentation/admin-guide/md.rst.
3818
3819 mdacon= [MDA]
3820 Format: <first>,<last>
3821 Specifies range of consoles to be captured by the MDA.
3822
3823 mds= [X86,INTEL,EARLY]
3824 Control mitigation for the Micro-architectural Data
3825 Sampling (MDS) vulnerability.
3826
3827 Certain CPUs are vulnerable to an exploit against CPU
3828 internal buffers which can forward information to a
3829 disclosure gadget under certain conditions.
3830
3831 In vulnerable processors, the speculatively
3832 forwarded data can be used in a cache side channel
3833 attack, to access data to which the attacker does
3834 not have direct access.
3835
3836 This parameter controls the MDS mitigation. The
3837 options are:
3838
3839 full - Enable MDS mitigation on vulnerable CPUs
3840 full,nosmt - Enable MDS mitigation and disable
3841 SMT on vulnerable CPUs
3842 off - Unconditionally disable MDS mitigation
3843
3844 On TAA-affected machines, mds=off can be prevented by
3845 an active TAA mitigation as both vulnerabilities are
3846 mitigated with the same mechanism so in order to disable
3847 this mitigation, you need to specify tsx_async_abort=off
3848 too.
3849
3850 Not specifying this option is equivalent to
3851 mds=full.
3852
3853 For details see: Documentation/admin-guide/hw-vuln/mds.rst
3854
3855 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size.
3856 Must be specified, otherwise memory size will be 0.
3857
3858 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount
3859 of memory Amount of memory to be used in cases
3860 as follows:
3861
3862 1 for test;
3863 2 when the kernel is not able to see the whole system memory;
3864 3 memory that lies after 'mem=' boundary is excluded from
3865 the hypervisor, then assigned to KVM guests.
3866 4 to limit the memory available for kdump kernel.
3867
3868 [ARC,MICROBLAZE] - the limit applies only to low memory,
3869 high memory is not affected.
3870
3871 [ARM64] - only limits memory covered by the linear
3872 mapping. The NOMAP regions are not affected.
3873
3874 [X86] Work as limiting max address. Use together
3875 with memmap= to avoid physical address space collisions.
3876 Without memmap= PCI devices could be placed at addresses
3877 belonging to unused RAM.
3878
3879 Note that this only takes effects during boot time since
3880 in above case 3, memory may need be hot added after boot
3881 if system memory of hypervisor is not sufficient.
3882
3883 mem=nn[KMG]@ss[KMG]
3884 [ARM,MIPS,EARLY] - override the memory layout
3885 reported by firmware.
3886 Define a memory region of size nn[KMG] starting at
3887 ss[KMG].
3888 Multiple different regions can be specified with
3889 multiple mem= parameters on the command line.
3890
3891 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
3892 memory.
3893
3894 memblock=debug [KNL,EARLY] Enable memblock debug messages.
3895
3896 memchunk=nn[KMG]
3897 [KNL,SH] Allow user to override the default size for
3898 per-device physically contiguous DMA buffers.
3899
3900 memhp_default_state=online/offline/online_kernel/online_movable
3901 [KNL] Set the initial state for the memory hotplug
3902 onlining policy. If not specified, the default value is
3903 set according to the
3904 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config
3905 options.
3906 See Documentation/admin-guide/mm/memory-hotplug.rst.
3907
3908 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact
3909 E820 memory map, as specified by the user.
3910 Such memmap=exactmap lines can be constructed based on
3911 BIOS output or other requirements. See the memmap=nn@ss
3912 option description.
3913
3914 memmap=nn[KMG]@ss[KMG]
3915 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory.
3916 Region of memory to be used is from ss to ss+nn.
3917 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3918 which limits max address to nn[KMG].
3919 Multiple different regions can be specified,
3920 comma delimited.
3921 Example:
3922 memmap=100M@2G,100M#3G,1G!1024G
3923
3924 memmap=nn[KMG]#ss[KMG]
3925 [KNL,ACPI,EARLY] Mark specific memory as ACPI data.
3926 Region of memory to be marked is from ss to ss+nn.
3927
3928 memmap=nn[KMG]$ss[KMG]
3929 [KNL,ACPI,EARLY] Mark specific memory as reserved.
3930 Region of memory to be reserved is from ss to ss+nn.
3931 Example: Exclude memory from 0x18690000-0x1869ffff
3932 memmap=64K$0x18690000
3933 or
3934 memmap=0x10000$0x18690000
3935 Some bootloaders may need an escape character before '$',
3936 like Grub2, otherwise '$' and the following number
3937 will be eaten.
3938
3939 memmap=nn[KMG]!ss[KMG,EARLY]
3940 [KNL,X86] Mark specific memory as protected.
3941 Region of memory to be used, from ss to ss+nn.
3942 The memory region may be marked as e820 type 12 (0xc)
3943 and is NVDIMM or ADR memory.
3944
3945 memmap=<size>%<offset>-<oldtype>+<newtype>
3946 [KNL,ACPI,EARLY] Convert memory within the specified region
3947 from <oldtype> to <newtype>. If "-<oldtype>" is left
3948 out, the whole region will be marked as <newtype>,
3949 even if previously unavailable. If "+<newtype>" is left
3950 out, matching memory will be removed. Types are
3951 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3952 3 = ACPI, 12 = PRAM.
3953
3954 memory_corruption_check=0/1 [X86,EARLY]
3955 Some BIOSes seem to corrupt the first 64k of
3956 memory when doing things like suspend/resume.
3957 Setting this option will scan the memory
3958 looking for corruption. Enabling this will
3959 both detect corruption and prevent the kernel
3960 from using the memory being corrupted.
3961 However, it's intended as a diagnostic tool; if
3962 repeatable BIOS-originated corruption always
3963 affects the same memory, you can use memmap=
3964 to prevent the kernel from using that memory.
3965
3966 memory_corruption_check_size=size [X86,EARLY]
3967 By default it checks for corruption in the low
3968 64k, making this memory unavailable for normal
3969 use. Use this parameter to scan for
3970 corruption in more or less memory.
3971
3972 memory_corruption_check_period=seconds [X86,EARLY]
3973 By default it checks for corruption every 60
3974 seconds. Use this parameter to check at some
3975 other rate. 0 disables periodic checking.
3976
3977 memory_hotplug.memmap_on_memory
3978 [KNL,X86,ARM] Boolean flag to enable this feature.
3979 Format: {on | off (default)}
3980 When enabled, runtime hotplugged memory will
3981 allocate its internal metadata (struct pages,
3982 those vmemmap pages cannot be optimized even
3983 if hugetlb_free_vmemmap is enabled) from the
3984 hotadded memory which will allow to hotadd a
3985 lot of memory without requiring additional
3986 memory to do so.
3987 This feature is disabled by default because it
3988 has some implication on large (e.g. GB)
3989 allocations in some configurations (e.g. small
3990 memory blocks).
3991 The state of the flag can be read in
3992 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3993 Note that even when enabled, there are a few cases where
3994 the feature is not effective.
3995
3996 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest
3997 Format: <integer>
3998 default : 0 <disable>
3999 Specifies the number of memtest passes to be
4000 performed. Each pass selects another test
4001 pattern from a given set of patterns. Memtest
4002 fills the memory with this pattern, validates
4003 memory contents and reserves bad memory
4004 regions that are detected.
4005
4006 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
4007 Valid arguments: on, off
4008 Default: off
4009 mem_encrypt=on: Activate SME
4010 mem_encrypt=off: Do not activate SME
4011
4012 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst
4013 for details on when memory encryption can be activated.
4014
4015 mem_sleep_default= [SUSPEND] Default system suspend mode:
4016 s2idle - Suspend-To-Idle
4017 shallow - Power-On Suspend or equivalent (if supported)
4018 deep - Suspend-To-RAM or equivalent (if supported)
4019 See Documentation/admin-guide/pm/sleep-states.rst.
4020
4021 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
4022 the BIOS has incorrectly applied a workaround. TinyBIOS
4023 version 0.98 is known to be affected, 0.99 fixes the
4024 problem by letting the user disable the workaround.
4025
4026 mga= [HW,DRM]
4027
4028 microcode= [X86] Control the behavior of the microcode loader.
4029 Available options, comma separated:
4030
4031 base_rev=X - with <X> with format: <u32>
4032 Set the base microcode revision of each thread when in
4033 debug mode.
4034
4035 dis_ucode_ldr: disable the microcode loader
4036
4037 force_minrev:
4038 Enable or disable the microcode minimal revision
4039 enforcement for the runtime microcode loader.
4040
4041 mini2440= [ARM,HW,KNL]
4042 Format:[0..2][b][c][t]
4043 Default: "0tb"
4044 MINI2440 configuration specification:
4045 0 - The attached screen is the 3.5" TFT
4046 1 - The attached screen is the 7" TFT
4047 2 - The VGA Shield is attached (1024x768)
4048 Leaving out the screen size parameter will not load
4049 the TFT driver, and the framebuffer will be left
4050 unconfigured.
4051 b - Enable backlight. The TFT backlight pin will be
4052 linked to the kernel VESA blanking code and a GPIO
4053 LED. This parameter is not necessary when using the
4054 VGA shield.
4055 c - Enable the s3c camera interface.
4056 t - Reserved for enabling touchscreen support. The
4057 touchscreen support is not enabled in the mainstream
4058 kernel as of 2.6.30, a preliminary port can be found
4059 in the "bleeding edge" mini2440 support kernel at
4060 https://repo.or.cz/w/linux-2.6/mini2440.git
4061
4062 mitigations=
4063 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for
4064 CPU vulnerabilities. This is a set of curated,
4065 arch-independent options, each of which is an
4066 aggregation of existing arch-specific options.
4067
4068 Note, "mitigations" is supported if and only if the
4069 kernel was built with CPU_MITIGATIONS=y.
4070
4071 off
4072 Disable all optional CPU mitigations. This
4073 improves system performance, but it may also
4074 expose users to several CPU vulnerabilities.
4075 Equivalent to: if nokaslr then kpti=0 [ARM64]
4076 gather_data_sampling=off [X86]
4077 indirect_target_selection=off [X86]
4078 kvm.nx_huge_pages=off [X86]
4079 l1tf=off [X86]
4080 mds=off [X86]
4081 mmio_stale_data=off [X86]
4082 no_entry_flush [PPC]
4083 no_uaccess_flush [PPC]
4084 nobp=0 [S390]
4085 nopti [X86,PPC]
4086 nospectre_bhb [ARM64]
4087 nospectre_v1 [X86,PPC]
4088 nospectre_v2 [X86,PPC,S390,ARM64]
4089 reg_file_data_sampling=off [X86]
4090 retbleed=off [X86]
4091 spec_rstack_overflow=off [X86]
4092 spec_store_bypass_disable=off [X86,PPC]
4093 spectre_bhi=off [X86]
4094 spectre_v2_user=off [X86]
4095 srbds=off [X86,INTEL]
4096 ssbd=force-off [ARM64]
4097 tsa=off [X86,AMD]
4098 tsx_async_abort=off [X86]
4099 vmscape=off [X86]
4100
4101 Exceptions:
4102 This does not have any effect on
4103 kvm.nx_huge_pages when
4104 kvm.nx_huge_pages=force.
4105
4106 auto (default)
4107 Mitigate all CPU vulnerabilities, but leave SMT
4108 enabled, even if it's vulnerable. This is for
4109 users who don't want to be surprised by SMT
4110 getting disabled across kernel upgrades, or who
4111 have other ways of avoiding SMT-based attacks.
4112 Equivalent to: (default behavior)
4113
4114 auto,nosmt
4115 Mitigate all CPU vulnerabilities, disabling SMT
4116 if needed. This is for users who always want to
4117 be fully mitigated, even if it means losing SMT.
4118 Equivalent to: l1tf=flush,nosmt [X86]
4119 mds=full,nosmt [X86]
4120 tsx_async_abort=full,nosmt [X86]
4121 mmio_stale_data=full,nosmt [X86]
4122 retbleed=auto,nosmt [X86]
4123
4124 [X86] After one of the above options, additionally
4125 supports attack-vector based controls as documented in
4126 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
4127
4128 mminit_loglevel=
4129 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this
4130 parameter allows control of the logging verbosity for
4131 the additional memory initialisation checks. A value
4132 of 0 disables mminit logging and a level of 4 will
4133 log everything. Information is printed at KERN_DEBUG
4134 so loglevel=8 may also need to be specified.
4135
4136 mmio_stale_data=
4137 [X86,INTEL,EARLY] Control mitigation for the Processor
4138 MMIO Stale Data vulnerabilities.
4139
4140 Processor MMIO Stale Data is a class of
4141 vulnerabilities that may expose data after an MMIO
4142 operation. Exposed data could originate or end in
4143 the same CPU buffers as affected by MDS and TAA.
4144 Therefore, similar to MDS and TAA, the mitigation
4145 is to clear the affected CPU buffers.
4146
4147 This parameter controls the mitigation. The
4148 options are:
4149
4150 full - Enable mitigation on vulnerable CPUs
4151
4152 full,nosmt - Enable mitigation and disable SMT on
4153 vulnerable CPUs.
4154
4155 off - Unconditionally disable mitigation
4156
4157 On MDS or TAA affected machines,
4158 mmio_stale_data=off can be prevented by an active
4159 MDS or TAA mitigation as these vulnerabilities are
4160 mitigated with the same mechanism so in order to
4161 disable this mitigation, you need to specify
4162 mds=off and tsx_async_abort=off too.
4163
4164 Not specifying this option is equivalent to
4165 mmio_stale_data=full.
4166
4167 For details see:
4168 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
4169
4170 <module>.async_probe[=<bool>] [KNL]
4171 If no <bool> value is specified or if the value
4172 specified is not a valid <bool>, enable asynchronous
4173 probe on this module. Otherwise, enable/disable
4174 asynchronous probe on this module as indicated by the
4175 <bool> value. See also: module.async_probe
4176
4177 module.async_probe=<bool>
4178 [KNL] When set to true, modules will use async probing
4179 by default. To enable/disable async probing for a
4180 specific module, use the module specific control that
4181 is documented under <module>.async_probe. When both
4182 module.async_probe and <module>.async_probe are
4183 specified, <module>.async_probe takes precedence for
4184 the specific module.
4185
4186 module.enable_dups_trace
4187 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set,
4188 this means that duplicate request_module() calls will
4189 trigger a WARN_ON() instead of a pr_warn(). Note that
4190 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
4191 will always be issued and this option does nothing.
4192 module.sig_enforce
4193 [KNL] When CONFIG_MODULE_SIG is set, this means that
4194 modules without (valid) signatures will fail to load.
4195 Note that if CONFIG_MODULE_SIG_FORCE is set, that
4196 is always true, so this option does nothing.
4197
4198 module_blacklist= [KNL] Do not load a comma-separated list of
4199 modules. Useful for debugging problem modules.
4200
4201 mousedev.tap_time=
4202 [MOUSE] Maximum time between finger touching and
4203 leaving touchpad surface for touch to be considered
4204 a tap and be reported as a left button click (for
4205 touchpads working in absolute mode only).
4206 Format: <msecs>
4207 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
4208 reporting absolute coordinates, such as tablets
4209 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
4210 reporting absolute coordinates, such as tablets
4211
4212 movablecore= [KNL,X86,PPC,EARLY]
4213 Format: nn[KMGTPE] | nn%
4214 This parameter is the complement to kernelcore=, it
4215 specifies the amount of memory used for migratable
4216 allocations. If both kernelcore and movablecore is
4217 specified, then kernelcore will be at *least* the
4218 specified value but may be more. If movablecore on its
4219 own is specified, the administrator must be careful
4220 that the amount of memory usable for all allocations
4221 is not too small.
4222
4223 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory
4224 NUMA nodes to be movable. This means that the memory
4225 of such nodes will be usable only for movable
4226 allocations which rules out almost all kernel
4227 allocations. Use with caution!
4228
4229 MTD_Partition= [MTD]
4230 Format: <name>,<region-number>,<size>,<offset>
4231
4232 MTD_Region= [MTD] Format:
4233 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
4234
4235 mtdparts= [MTD]
4236 See drivers/mtd/parsers/cmdlinepart.c
4237
4238 mtouchusb.raw_coordinates=
4239 [HW] Make the MicroTouch USB driver use raw coordinates
4240 ('y', default) or cooked coordinates ('n')
4241
4242 mtrr=debug [X86,EARLY]
4243 Enable printing debug information related to MTRR
4244 registers at boot time.
4245
4246 mtrr_chunk_size=nn[KMG,X86,EARLY]
4247 used for mtrr cleanup. It is largest continuous chunk
4248 that could hold holes aka. UC entries.
4249
4250 mtrr_gran_size=nn[KMG,X86,EARLY]
4251 Used for mtrr cleanup. It is granularity of mtrr block.
4252 Default is 1.
4253 Large value could prevent small alignment from
4254 using up MTRRs.
4255
4256 mtrr_spare_reg_nr=n [X86,EARLY]
4257 Format: <integer>
4258 Range: 0,7 : spare reg number
4259 Default : 1
4260 Used for mtrr cleanup. It is spare mtrr entries number.
4261 Set to 2 or more if your graphical card needs more.
4262
4263 multitce=off [PPC] This parameter disables the use of the pSeries
4264 firmware feature for updating multiple TCE entries
4265 at a time.
4266
4267 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
4268
4269 netdev= [NET] Network devices parameters
4270 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
4271 Note that mem_start is often overloaded to mean
4272 something different and driver-specific.
4273 This usage is only documented in each driver source
4274 file if at all.
4275
4276 netpoll.carrier_timeout=
4277 [NET] Specifies amount of time (in seconds) that
4278 netpoll should wait for a carrier. By default netpoll
4279 waits 4 seconds.
4280
4281 nf_conntrack.acct=
4282 [NETFILTER] Enable connection tracking flow accounting
4283 0 to disable accounting
4284 1 to enable accounting
4285 Default value is 0.
4286
4287 nfs.cache_getent=
4288 [NFS] sets the pathname to the program which is used
4289 to update the NFS client cache entries.
4290
4291 nfs.cache_getent_timeout=
4292 [NFS] sets the timeout after which an attempt to
4293 update a cache entry is deemed to have failed.
4294
4295 nfs.callback_nr_threads=
4296 [NFSv4] set the total number of threads that the
4297 NFS client will assign to service NFSv4 callback
4298 requests.
4299
4300 nfs.callback_tcpport=
4301 [NFS] set the TCP port on which the NFSv4 callback
4302 channel should listen.
4303
4304 nfs.delay_retrans=
4305 [NFS] specifies the number of times the NFSv4 client
4306 retries the request before returning an EAGAIN error,
4307 after a reply of NFS4ERR_DELAY from the server.
4308 Only applies if the softerr mount option is enabled,
4309 and the specified value is >= 0.
4310
4311 nfs.enable_ino64=
4312 [NFS] enable 64-bit inode numbers.
4313 If zero, the NFS client will fake up a 32-bit inode
4314 number for the readdir() and stat() syscalls instead
4315 of returning the full 64-bit number.
4316 The default is to return 64-bit inode numbers.
4317
4318 nfs.idmap_cache_timeout=
4319 [NFS] set the maximum lifetime for idmapper cache
4320 entries.
4321
4322 nfs.max_session_cb_slots=
4323 [NFSv4.1] Sets the maximum number of session
4324 slots the client will assign to the callback
4325 channel. This determines the maximum number of
4326 callbacks the client will process in parallel for
4327 a particular server.
4328
4329 nfs.max_session_slots=
4330 [NFSv4.1] Sets the maximum number of session slots
4331 the client will attempt to negotiate with the server.
4332 This limits the number of simultaneous RPC requests
4333 that the client can send to the NFSv4.1 server.
4334 Note that there is little point in setting this
4335 value higher than the max_tcp_slot_table_limit.
4336
4337 nfs.nfs4_disable_idmapping=
4338 [NFSv4] When set to the default of '1', this option
4339 ensures that both the RPC level authentication
4340 scheme and the NFS level operations agree to use
4341 numeric uids/gids if the mount is using the
4342 'sec=sys' security flavour. In effect it is
4343 disabling idmapping, which can make migration from
4344 legacy NFSv2/v3 systems to NFSv4 easier.
4345 Servers that do not support this mode of operation
4346 will be autodetected by the client, and it will fall
4347 back to using the idmapper.
4348 To turn off this behaviour, set the value to '0'.
4349
4350 nfs.nfs4_unique_id=
4351 [NFS4] Specify an additional fixed unique ident-
4352 ification string that NFSv4 clients can insert into
4353 their nfs_client_id4 string. This is typically a
4354 UUID that is generated at system install time.
4355
4356 nfs.recover_lost_locks=
4357 [NFSv4] Attempt to recover locks that were lost due
4358 to a lease timeout on the server. Please note that
4359 doing this risks data corruption, since there are
4360 no guarantees that the file will remain unchanged
4361 after the locks are lost.
4362 If you want to enable the kernel legacy behaviour of
4363 attempting to recover these locks, then set this
4364 parameter to '1'.
4365 The default parameter value of '0' causes the kernel
4366 not to attempt recovery of lost locks.
4367
4368 nfs.send_implementation_id=
4369 [NFSv4.1] Send client implementation identification
4370 information in exchange_id requests.
4371 If zero, no implementation identification information
4372 will be sent.
4373 The default is to send the implementation identification
4374 information.
4375
4376 nfs4.layoutstats_timer=
4377 [NFSv4.2] Change the rate at which the kernel sends
4378 layoutstats to the pNFS metadata server.
4379
4380 Setting this to value to 0 causes the kernel to use
4381 whatever value is the default set by the layout
4382 driver. A non-zero value sets the minimum interval
4383 in seconds between layoutstats transmissions.
4384
4385 nfsd.inter_copy_offload_enable=
4386 [NFSv4.2] When set to 1, the server will support
4387 server-to-server copies for which this server is
4388 the destination of the copy.
4389
4390 nfsd.nfs4_disable_idmapping=
4391 [NFSv4] When set to the default of '1', the NFSv4
4392 server will return only numeric uids and gids to
4393 clients using auth_sys, and will accept numeric uids
4394 and gids from such clients. This is intended to ease
4395 migration from NFSv2/v3.
4396
4397 nfsd.nfsd4_ssc_umount_timeout=
4398 [NFSv4.2] When used as the destination of a
4399 server-to-server copy, knfsd temporarily mounts
4400 the source server. It caches the mount in case
4401 it will be needed again, and discards it if not
4402 used for the number of milliseconds specified by
4403 this parameter.
4404
4405 nfsaddrs= [NFS] Deprecated. Use ip= instead.
4406 See Documentation/admin-guide/nfs/nfsroot.rst.
4407
4408 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
4409 See Documentation/admin-guide/nfs/nfsroot.rst.
4410
4411 nfsrootdebug [NFS] enable nfsroot debugging messages.
4412 See Documentation/admin-guide/nfs/nfsroot.rst.
4413
4414 nmi_backtrace.backtrace_idle [KNL]
4415 Dump stacks even of idle CPUs in response to an
4416 NMI stack-backtrace request.
4417
4418 nmi_debug= [KNL,SH] Specify one or more actions to take
4419 when a NMI is triggered.
4420 Format: [state][,regs][,debounce][,die]
4421
4422 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
4423 Format: [panic,][nopanic,][rNNN,][num]
4424 Valid num: 0 or 1
4425 0 - turn hardlockup detector in nmi_watchdog off
4426 1 - turn hardlockup detector in nmi_watchdog on
4427 rNNN - configure the watchdog with raw perf event 0xNNN
4428
4429 When panic is specified, panic when an NMI watchdog
4430 timeout occurs (or 'nopanic' to not panic on an NMI
4431 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
4432 To disable both hard and soft lockup detectors,
4433 please see 'nowatchdog'.
4434 This is useful when you use a panic=... timeout and
4435 need the box quickly up again.
4436
4437 These settings can be accessed at runtime via
4438 the nmi_watchdog and hardlockup_panic sysctls.
4439
4440 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
4441 emulation library even if a 387 maths coprocessor
4442 is present.
4443
4444 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes.
4445 Forces kernel to use 3-level paging instead.
4446
4447 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces
4448 kernel to use 4-level paging instead.
4449
4450 noalign [KNL,ARM]
4451
4452 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any
4453 IOAPICs that may be present in the system.
4454
4455 noapictimer [APIC,X86] Don't set up the APIC timer
4456
4457 noautogroup Disable scheduler automatic task group creation.
4458
4459 nocache [ARM,EARLY]
4460
4461 no_console_suspend
4462 [HW] Never suspend the console
4463 Disable suspending of consoles during suspend and
4464 hibernate operations. Once disabled, debugging
4465 messages can reach various consoles while the rest
4466 of the system is being put to sleep (ie, while
4467 debugging driver suspend/resume hooks). This may
4468 not work reliably with all consoles, but is known
4469 to work with serial and VGA consoles.
4470 To facilitate more flexible debugging, we also add
4471 console_suspend, a printk module parameter to control
4472 it. Users could use console_suspend (usually
4473 /sys/module/printk/parameters/console_suspend) to
4474 turn on/off it dynamically.
4475
4476 no_debug_objects
4477 [KNL,EARLY] Disable object debugging
4478
4479 nodsp [SH] Disable hardware DSP at boot time.
4480
4481 noefi [EFI,EARLY] Disable EFI runtime services support.
4482
4483 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel.
4484
4485 noexec32 [X86-64]
4486 This affects only 32-bit executables.
4487 noexec32=on: enable non-executable mappings (default)
4488 read doesn't imply executable mappings
4489 noexec32=off: disable non-executable mappings
4490 read implies executable mappings
4491
4492 no_file_caps Tells the kernel not to honor file capabilities. The
4493 only way then for a file to be executed with privilege
4494 is to be setuid root or executed by root.
4495
4496 nofpu [MIPS,SH] Disable hardware FPU at boot time.
4497
4498 nofsgsbase [X86] Disables FSGSBASE instructions.
4499
4500 nofxsr [BUGS=X86-32] Disables x86 floating point extended
4501 register save and restore. The kernel will only save
4502 legacy floating-point registers on task switch.
4503
4504 nogbpages [X86] Do not use GB pages for kernel direct mappings.
4505
4506 no_hash_pointers
4507 [KNL,EARLY]
4508 Alias for "hash_pointers=never".
4509
4510 nohibernate [HIBERNATION] Disable hibernation and resume.
4511
4512 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to
4513 busy wait in do_idle() and not use the arch_cpu_idle()
4514 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
4515 to be effective. This is useful on platforms where the
4516 sleep(SH) or wfi(ARM,ARM64) instructions do not work
4517 correctly or when doing power measurements to evaluate
4518 the impact of the sleep instructions. This is also
4519 useful when using JTAG debugger.
4520
4521 nohpet [X86] Don't use the HPET timer.
4522
4523 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings.
4524
4525 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings.
4526
4527 nohz= [KNL] Boottime enable/disable dynamic ticks
4528 Valid arguments: on, off
4529 Default: on
4530
4531 nohz_full= [KNL,BOOT,SMP,ISOL]
4532 The argument is a cpu list, as described above.
4533 In kernels built with CONFIG_NO_HZ_FULL=y, set
4534 the specified list of CPUs whose tick will be stopped
4535 whenever possible. The boot CPU will be forced outside
4536 the range to maintain the timekeeping. Any CPUs
4537 in this list will have their RCU callbacks offloaded,
4538 just as if they had also been called out in the
4539 rcu_nocbs= boot parameter.
4540
4541 Note that this argument takes precedence over
4542 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
4543
4544 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured
4545 initial RAM disk. Currently this parameter applies to
4546 initrd only, not to initramfs. But it applies to both
4547 in EFI mode.
4548
4549 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt
4550 remapping.
4551 [Deprecated - use intremap=off]
4552
4553 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature.
4554
4555 noiotrap [SH] Disables trapped I/O port accesses.
4556
4557 noirqdebug [X86-32] Disables the code which attempts to detect and
4558 disable unhandled interrupt sources.
4559
4560 noisapnp [ISAPNP] Disables ISA PnP code.
4561
4562 nokaslr [KNL,EARLY]
4563 When CONFIG_RANDOMIZE_BASE is set, this disables
4564 kernel and module base offset ASLR (Address Space
4565 Layout Randomization).
4566
4567 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page
4568 fault handling.
4569
4570 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver
4571
4572 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC.
4573
4574 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer.
4575
4576 nomce [X86-32] Disable Machine Check Exception
4577
4578 nomfgpt [X86-32] Disable Multi-Function General Purpose
4579 Timer usage (for AMD Geode machines).
4580
4581 nomodeset Disable kernel modesetting. Most systems' firmware
4582 sets up a display mode and provides framebuffer memory
4583 for output. With nomodeset, DRM and fbdev drivers will
4584 not load if they could possibly displace the pre-
4585 initialized output. Only the system framebuffer will
4586 be available for use. The respective drivers will not
4587 perform display-mode changes or accelerated rendering.
4588
4589 Useful as error fallback, or for testing and debugging.
4590
4591 nomodule Disable module load
4592
4593 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
4594 shutdown the other cpus. Instead use the REBOOT_VECTOR
4595 irq.
4596
4597 nopat [X86,EARLY] Disable PAT (page attribute table extension of
4598 pagetables) support.
4599
4600 nopcid [X86-64,EARLY] Disable the PCID cpu feature.
4601
4602 nopku [X86] Disable Memory Protection Keys CPU feature found
4603 in some Intel CPUs.
4604
4605 nopti [X86-64,EARLY]
4606 Equivalent to pti=off
4607
4608 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY]
4609 Disables the PV optimizations forcing the guest to run
4610 as generic guest with no PV drivers. Currently support
4611 XEN HVM, KVM, HYPER_V and VMWARE guest.
4612
4613 nopvspin [X86,XEN,KVM,EARLY]
4614 Disables the qspinlock slow path using PV optimizations
4615 which allow the hypervisor to 'idle' the guest on lock
4616 contention.
4617
4618 norandmaps Don't use address space randomization. Equivalent to
4619 echo 0 > /proc/sys/kernel/randomize_va_space
4620
4621 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
4622 with UP alternatives
4623
4624 noresume [SWSUSP] Disables resume and restores original swap
4625 space.
4626
4627 no-scroll [VGA] Disables scrollback.
4628 This is required for the Braillex ib80-piezo Braille
4629 reader made by F.H. Papenmeier (Germany).
4630
4631 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support.
4632
4633 nosmap [PPC,EARLY]
4634 Disable SMAP (Supervisor Mode Access Prevention)
4635 even if it is supported by processor.
4636
4637 nosmep [PPC64s,EARLY]
4638 Disable SMEP (Supervisor Mode Execution Prevention)
4639 even if it is supported by processor.
4640
4641 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel,
4642 and disable the IO APIC. legacy for "maxcpus=0".
4643
4644 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT).
4645 Equivalent to smt=1.
4646
4647 [KNL,LOONGARCH,X86,PPC,S390] Disable symmetric multithreading (SMT).
4648 nosmt=force: Force disable SMT, cannot be undone
4649 via the sysfs control file.
4650
4651 nosoftlockup [KNL] Disable the soft-lockup detector.
4652
4653 nospec_store_bypass_disable
4654 [HW,EARLY] Disable all mitigations for the Speculative
4655 Store Bypass vulnerability
4656
4657 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch
4658 history injection) vulnerability. System may allow data leaks
4659 with this option.
4660
4661 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1
4662 (bounds check bypass). With this option data leaks are
4663 possible in the system.
4664
4665 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations
4666 for the Spectre variant 2 (indirect branch
4667 prediction) vulnerability. System may allow data
4668 leaks with this option.
4669
4670 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY]
4671 Disable paravirtualized steal time accounting. steal time
4672 is computed, but won't influence scheduler behaviour
4673
4674 nosync [HW,M68K] Disables sync negotiation for all devices.
4675
4676 no_timer_check [X86,APIC] Disables the code which tests for broken
4677 timer IRQ sources, i.e., the IO-APIC timer. This can
4678 work around problems with incorrect timer
4679 initialization on some boards.
4680
4681 no_uaccess_flush
4682 [PPC,EARLY] Don't flush the L1-D cache after accessing user data.
4683
4684 novmcoredd [KNL,KDUMP]
4685 Disable device dump. Device dump allows drivers to
4686 append dump data to vmcore so you can collect driver
4687 specified debug info. Drivers can append the data
4688 without any limit and this data is stored in memory,
4689 so this may cause significant memory stress. Disabling
4690 device dump can help save memory but the driver debug
4691 data will be no longer available. This parameter
4692 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
4693 is set.
4694
4695 no-vmw-sched-clock
4696 [X86,PV_OPS,EARLY] Disable paravirtualized VMware
4697 scheduler clock and use the default one.
4698
4699 nowatchdog [KNL] Disable both lockup detectors, i.e.
4700 soft-lockup and NMI watchdog (hard-lockup).
4701
4702 nowb [ARM,EARLY]
4703
4704 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode.
4705
4706 NOTE: this parameter will be ignored on systems with the
4707 LEGACY_XAPIC_DISABLED bit set in the
4708 IA32_XAPIC_DISABLE_STATUS MSR.
4709
4710 noxsave [BUGS=X86] Disables x86 extended register state save
4711 and restore using xsave. The kernel will fallback to
4712 enabling legacy floating-point and sse state.
4713
4714 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
4715 register states. The kernel will fall back to use
4716 xsave to save the states. By using this parameter,
4717 performance of saving the states is degraded because
4718 xsave doesn't support modified optimization while
4719 xsaveopt supports it on xsaveopt enabled systems.
4720
4721 noxsaves [X86] Disables xsaves and xrstors used in saving and
4722 restoring x86 extended register state in compacted
4723 form of xsave area. The kernel will fall back to use
4724 xsaveopt and xrstor to save and restore the states
4725 in standard form of xsave area. By using this
4726 parameter, xsave area per process might occupy more
4727 memory on xsaves enabled systems.
4728
4729 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
4730 could support. nr_cpus=n : n >= 1 limits the kernel to
4731 support 'n' processors. It could be larger than the
4732 number of already plugged CPU during bootup, later in
4733 runtime you can physically add extra cpu until it reaches
4734 n. So during boot up some boot time memory for per-cpu
4735 variables need be pre-allocated for later physical cpu
4736 hot plugging.
4737
4738 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
4739
4740 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY]
4741 Disable NUMA, Only set up a single NUMA node
4742 spanning all memory.
4743
4744 numa=fake=<size>[MG]
4745 [KNL, ARM64, RISCV, X86, EARLY]
4746 If given as a memory unit, fills all system RAM with
4747 nodes of size interleaved over physical nodes.
4748
4749 numa=fake=<N>
4750 [KNL, ARM64, RISCV, X86, EARLY]
4751 If given as an integer, fills all system RAM with N
4752 fake nodes interleaved over physical nodes.
4753
4754 numa=fake=<N>U
4755 [KNL, ARM64, RISCV, X86, EARLY]
4756 If given as an integer followed by 'U', it will
4757 divide each physical node into N emulated nodes.
4758
4759 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup
4760
4761 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or
4762 soft-reserved memory partitioning.
4763
4764 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
4765 NUMA balancing.
4766 Allowed values are enable and disable
4767
4768 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
4769 'node', 'default' can be specified
4770 This can be set from sysctl after boot.
4771 See Documentation/admin-guide/sysctl/vm.rst for details.
4772
4773 nvme.quirks= [NVME] A list of quirk entries to augment the built-in
4774 nvme quirk list. List entries are separated by a
4775 '-' character.
4776 Each entry has the form VendorID:ProductID:quirk_names.
4777 The IDs are 4-digits hex numbers and quirk_names is a
4778 list of quirk names separated by commas. A quirk name
4779 can be prefixed by '^', meaning that the specified
4780 quirk must be disabled.
4781
4782 Example:
4783 nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi
4784
4785 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver.
4786 See Documentation/core-api/debugging-via-ohci1394.rst for more
4787 info.
4788
4789 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
4790 Rather than timing out after 20 ms if an EC
4791 command is not properly ACKed, override the length
4792 of the timeout. We have interrupts disabled while
4793 waiting for the ACK, so if this is set too high
4794 interrupts *may* be lost!
4795
4796 omap_mux= [OMAP] Override bootloader pin multiplexing.
4797 Format: <mux_mode0.mode_name=value>...
4798 For example, to override I2C bus2:
4799 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
4800
4801 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
4802
4803 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
4804
4805 boundary - index of last SLC block on Flex-OneNAND.
4806 The remaining blocks are configured as MLC blocks.
4807 lock - Configure if Flex-OneNAND boundary should be locked.
4808 Once locked, the boundary cannot be changed.
4809 1 indicates lock status, 0 indicates unlock status.
4810
4811 oops=panic [KNL,EARLY]
4812 Always panic on oopses. Default is to just kill the
4813 process, but there is a small probability of
4814 deadlocking the machine.
4815 This will also cause panics on machine check exceptions.
4816 Useful together with panic=30 to trigger a reboot.
4817
4818 page_alloc.shuffle=
4819 [KNL] Boolean flag to control whether the page allocator
4820 should randomize its free lists. This parameter can be
4821 used to enable/disable page randomization. The state of
4822 the flag can be read from sysfs at:
4823 /sys/module/page_alloc/parameters/shuffle.
4824 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y.
4825
4826 page_owner= [KNL,EARLY] Boot-time page_owner enabling option.
4827 Storage of the information about who allocated
4828 each page is disabled in default. With this switch,
4829 we can turn it on.
4830 on: enable the feature
4831
4832 page_poison= [KNL,EARLY] Boot-time parameter changing the state of
4833 poisoning on the buddy allocator, available with
4834 CONFIG_PAGE_POISONING=y.
4835 off: turn off poisoning (default)
4836 on: turn on poisoning
4837
4838 page_reporting.page_reporting_order=
4839 [KNL] Minimal page reporting order
4840 Format: <integer>
4841 Adjust the minimal page reporting order. The page
4842 reporting is disabled when it exceeds MAX_PAGE_ORDER.
4843
4844 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4845 timeout > 0: seconds before rebooting
4846 timeout = 0: wait forever
4847 timeout < 0: reboot immediately
4848 Format: <timeout>
4849
4850 panic_on_taint= [KNL,EARLY]
4851 Bitmask for conditionally calling panic() in add_taint()
4852 Format: <hex>[,nousertaint]
4853 Hexadecimal bitmask representing the set of TAINT flags
4854 that will cause the kernel to panic when add_taint() is
4855 called with any of the flags in this set.
4856 The optional switch "nousertaint" can be utilized to
4857 prevent userspace forced crashes by writing to sysctl
4858 /proc/sys/kernel/tainted any flagset matching with the
4859 bitmask set on panic_on_taint.
4860 See Documentation/admin-guide/tainted-kernels.rst for
4861 extra details on the taint flags that users can pick
4862 to compose the bitmask to assign to panic_on_taint.
4863
4864 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump
4865 on a WARN().
4866
4867 panic_force_cpu=
4868 [KNL,SMP] Force panic handling to execute on a specific CPU.
4869 Format: <cpu number>
4870 Some platforms require panic handling to occur on a
4871 specific CPU for the crash kernel to function correctly.
4872 This can be due to firmware limitations, interrupt routing
4873 constraints, or platform-specific requirements where only
4874 a particular CPU can safely enter the crash kernel.
4875 When set, panic() will redirect execution to the specified
4876 CPU before proceeding with the normal panic and kexec flow.
4877 If the target CPU is offline or unavailable, panic proceeds
4878 on the current CPU.
4879 This option should only be used for systems with the above
4880 constraints as it might cause the panic operation to be less reliable.
4881
4882 panic_print= Bitmask for printing system info when panic happens.
4883 User can chose combination of the following bits:
4884 bit 0: print all tasks info
4885 bit 1: print system memory info
4886 bit 2: print timer info
4887 bit 3: print locks info if CONFIG_LOCKDEP is on
4888 bit 4: print ftrace buffer
4889 bit 5: replay all kernel messages on consoles at the end of panic
4890 bit 6: print all CPUs backtrace (if available in the arch)
4891 bit 7: print only tasks in uninterruptible (blocked) state
4892 *Be aware* that this option may print a _lot_ of lines,
4893 so there are risks of losing older messages in the log.
4894 Use this option carefully, maybe worth to setup a
4895 bigger log buffer with "log_buf_len" along with this.
4896
4897 panic_sys_info= A comma separated list of extra information to be dumped
4898 on panic.
4899 Format: val[,val...]
4900 Where @val can be any of the following:
4901
4902 tasks: print all tasks info
4903 mem: print system memory info
4904 timers: print timers info
4905 locks: print locks info if CONFIG_LOCKDEP is on
4906 ftrace: print ftrace buffer
4907 all_bt: print all CPUs backtrace (if available in the arch)
4908 blocked_tasks: print only tasks in uninterruptible (blocked) state
4909
4910 This is a human readable alternative to the 'panic_print' option.
4911
4912 panic_console_replay
4913 When panic happens, replay all kernel messages on
4914 consoles at the end of panic.
4915
4916 parkbd.port= [HW] Parallel port number the keyboard adapter is
4917 connected to, default is 0.
4918 Format: <parport#>
4919 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
4920 0 for XT, 1 for AT (default is AT).
4921 Format: <mode>
4922
4923 parport= [HW,PPT] Specify parallel ports. 0 disables.
4924 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
4925 Use 'auto' to force the driver to use any
4926 IRQ/DMA settings detected (the default is to
4927 ignore detected IRQ/DMA settings because of
4928 possible conflicts). You can specify the base
4929 address, IRQ, and DMA settings; IRQ and DMA
4930 should be numbers, or 'auto' (for using detected
4931 settings on that particular port), or 'nofifo'
4932 (to avoid using a FIFO even if it is detected).
4933 Parallel ports are assigned in the order they
4934 are specified on the command line, starting
4935 with parport0.
4936
4937 parport_init_mode= [HW,PPT]
4938 Configure VIA parallel port to operate in
4939 a specific mode. This is necessary on Pegasos
4940 computer where firmware has no options for setting
4941 up parallel port mode and sets it to spp.
4942 Currently this function knows 686a and 8231 chips.
4943 Format: [spp|ps2|epp|ecp|ecpepp]
4944
4945 pata_legacy.all= [HW,LIBATA]
4946 Format: <int>
4947 Set to non-zero to probe primary and secondary ISA
4948 port ranges on PCI systems where no PCI PATA device
4949 has been found at either range. Disabled by default.
4950
4951 pata_legacy.autospeed= [HW,LIBATA]
4952 Format: <int>
4953 Set to non-zero if a chip is present that snoops speed
4954 changes. Disabled by default.
4955
4956 pata_legacy.ht6560a= [HW,LIBATA]
4957 Format: <int>
4958 Set to 1, 2, or 3 for HT 6560A on the primary channel,
4959 the secondary channel, or both channels respectively.
4960 Disabled by default.
4961
4962 pata_legacy.ht6560b= [HW,LIBATA]
4963 Format: <int>
4964 Set to 1, 2, or 3 for HT 6560B on the primary channel,
4965 the secondary channel, or both channels respectively.
4966 Disabled by default.
4967
4968 pata_legacy.iordy_mask= [HW,LIBATA]
4969 Format: <int>
4970 IORDY enable mask. Set individual bits to allow IORDY
4971 for the respective channel. Bit 0 is for the first
4972 legacy channel handled by this driver, bit 1 is for
4973 the second channel, and so on. The sequence will often
4974 correspond to the primary legacy channel, the secondary
4975 legacy channel, and so on, but the handling of a PCI
4976 bus and the use of other driver options may interfere
4977 with the sequence. By default IORDY is allowed across
4978 all channels.
4979
4980 pata_legacy.opti82c46x= [HW,LIBATA]
4981 Format: <int>
4982 Set to 1, 2, or 3 for Opti 82c611A on the primary
4983 channel, the secondary channel, or both channels
4984 respectively. Disabled by default.
4985
4986 pata_legacy.opti82c611a= [HW,LIBATA]
4987 Format: <int>
4988 Set to 1, 2, or 3 for Opti 82c465MV on the primary
4989 channel, the secondary channel, or both channels
4990 respectively. Disabled by default.
4991
4992 pata_legacy.pio_mask= [HW,LIBATA]
4993 Format: <int>
4994 PIO mode mask for autospeed devices. Set individual
4995 bits to allow the use of the respective PIO modes.
4996 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
4997 All modes allowed by default.
4998
4999 pata_legacy.probe_all= [HW,LIBATA]
5000 Format: <int>
5001 Set to non-zero to probe tertiary and further ISA
5002 port ranges on PCI systems. Disabled by default.
5003
5004 pata_legacy.probe_mask= [HW,LIBATA]
5005 Format: <int>
5006 Probe mask for legacy ISA PATA ports. Depending on
5007 platform configuration and the use of other driver
5008 options up to 6 legacy ports are supported: 0x1f0,
5009 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
5010 of individual ports can be disabled by setting the
5011 corresponding bits in the mask to 1. Bit 0 is for
5012 the first port in the list above (0x1f0), and so on.
5013 By default all supported ports are probed.
5014
5015 pata_legacy.qdi= [HW,LIBATA]
5016 Format: <int>
5017 Set to non-zero to probe QDI controllers. By default
5018 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
5019
5020 pata_legacy.winbond= [HW,LIBATA]
5021 Format: <int>
5022 Set to non-zero to probe Winbond controllers. Use
5023 the standard I/O port (0x130) if 1, otherwise the
5024 value given is the I/O port to use (typically 0x1b0).
5025 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
5026 0 otherwise.
5027
5028 pata_platform.pio_mask= [HW,LIBATA]
5029 Format: <int>
5030 Supported PIO mode mask. Set individual bits to allow
5031 the use of the respective PIO modes. Bit 0 is for
5032 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
5033 allowed by default.
5034
5035 pause_on_oops=<int>
5036 Halt all CPUs after the first oops has been printed for
5037 the specified number of seconds. This is to be used if
5038 your oopses keep scrolling off the screen.
5039
5040 pcbit= [HW,ISDN]
5041
5042 pci=option[,option...] [PCI,EARLY] various PCI subsystem options.
5043
5044 Some options herein operate on a specific device
5045 or a set of devices (<pci_dev>). These are
5046 specified in one of the following formats:
5047
5048 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
5049 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
5050
5051 Note: the first format specifies a PCI
5052 bus/device/function address which may change
5053 if new hardware is inserted, if motherboard
5054 firmware changes, or due to changes caused
5055 by other kernel parameters. If the
5056 domain is left unspecified, it is
5057 taken to be zero. Optionally, a path
5058 to a device through multiple device/function
5059 addresses can be specified after the base
5060 address (this is more robust against
5061 renumbering issues). The second format
5062 selects devices using IDs from the
5063 configuration space which may match multiple
5064 devices in the system.
5065
5066 earlydump dump PCI config space before the kernel
5067 changes anything
5068 off [X86] don't probe for the PCI bus
5069 bios [X86-32] force use of PCI BIOS, don't access
5070 the hardware directly. Use this if your machine
5071 has a non-standard PCI host bridge.
5072 nobios [X86-32] disallow use of PCI BIOS, only direct
5073 hardware access methods are allowed. Use this
5074 if you experience crashes upon bootup and you
5075 suspect they are caused by the BIOS.
5076 conf1 [X86] Force use of PCI Configuration Access
5077 Mechanism 1 (config address in IO port 0xCF8,
5078 data in IO port 0xCFC, both 32-bit).
5079 conf2 [X86] Force use of PCI Configuration Access
5080 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
5081 the function, IO port 0xCFA, also 8-bit, sets
5082 bus number. The config space is then accessed
5083 through ports 0xC000-0xCFFF).
5084 See http://wiki.osdev.org/PCI for more info
5085 on the configuration access mechanisms.
5086 noaer [PCIE] If the PCIEAER kernel config parameter is
5087 enabled, this kernel boot option can be used to
5088 disable the use of PCIE advanced error reporting.
5089 nodomains [PCI] Disable support for multiple PCI
5090 root domains (aka PCI segments, in ACPI-speak).
5091 nommconf [X86] Disable use of MMCONFIG for PCI
5092 Configuration
5093 check_enable_amd_mmconf [X86] check for and enable
5094 properly configured MMIO access to PCI
5095 config space on AMD family 10h CPU
5096 nomsi [MSI] If the PCI_MSI kernel config parameter is
5097 enabled, this kernel boot option can be used to
5098 disable the use of MSI interrupts system-wide.
5099 noioapicquirk [APIC] Disable all boot interrupt quirks.
5100 Safety option to keep boot IRQs enabled. This
5101 should never be necessary.
5102 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
5103 primary IO-APIC for bridges that cannot disable
5104 boot IRQs. This fixes a source of spurious IRQs
5105 when the system masks IRQs.
5106 noioapicreroute [APIC] Disable workaround that uses the
5107 boot IRQ equivalent of an IRQ that connects to
5108 a chipset where boot IRQs cannot be disabled.
5109 The opposite of ioapicreroute.
5110 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
5111 routing table. These calls are known to be buggy
5112 on several machines and they hang the machine
5113 when used, but on other computers it's the only
5114 way to get the interrupt routing table. Try
5115 this option if the kernel is unable to allocate
5116 IRQs or discover secondary PCI buses on your
5117 motherboard.
5118 rom [X86] Assign address space to expansion ROMs.
5119 Use with caution as certain devices share
5120 address decoders between ROMs and other
5121 resources.
5122 norom [X86] Do not assign address space to
5123 expansion ROMs that do not already have
5124 BIOS assigned address ranges.
5125 nobar [X86] Do not assign address space to the
5126 BARs that weren't assigned by the BIOS.
5127 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
5128 assigned automatically to PCI devices. You can
5129 make the kernel exclude IRQs of your ISA cards
5130 this way.
5131 pirqaddr=0xAAAAA [X86] Specify the physical address
5132 of the PIRQ table (normally generated
5133 by the BIOS) if it is outside the
5134 F0000h-100000h range.
5135 lastbus=N [X86] Scan all buses thru bus #N. Can be
5136 useful if the kernel is unable to find your
5137 secondary buses and you want to tell it
5138 explicitly which ones they are.
5139 assign-busses [X86] Always assign all PCI bus
5140 numbers ourselves, overriding
5141 whatever the firmware may have done.
5142 usepirqmask [X86] Honor the possible IRQ mask stored
5143 in the BIOS $PIR table. This is needed on
5144 some systems with broken BIOSes, notably
5145 some HP Pavilion N5400 and Omnibook XE3
5146 notebooks. This will have no effect if ACPI
5147 IRQ routing is enabled.
5148 noacpi [X86] Do not use ACPI for IRQ routing
5149 or for PCI scanning.
5150 use_crs [X86] Use PCI host bridge window information
5151 from ACPI. On BIOSes from 2008 or later, this
5152 is enabled by default. If you need to use this,
5153 please report a bug.
5154 nocrs [X86] Ignore PCI host bridge windows from ACPI.
5155 If you need to use this, please report a bug.
5156 use_e820 [X86] Use E820 reservations to exclude parts of
5157 PCI host bridge windows. This is a workaround
5158 for BIOS defects in host bridge _CRS methods.
5159 If you need to use this, please report a bug to
5160 <linux-pci@vger.kernel.org>.
5161 no_e820 [X86] Ignore E820 reservations for PCI host
5162 bridge windows. This is the default on modern
5163 hardware. If you need to use this, please report
5164 a bug to <linux-pci@vger.kernel.org>.
5165 routeirq Do IRQ routing for all PCI devices.
5166 This is normally done in pci_enable_device(),
5167 so this option is a temporary workaround
5168 for broken drivers that don't call it.
5169 skip_isa_align [X86] do not align io start addr, so can
5170 handle more pci cards
5171 noearly [X86] Don't do any early type 1 scanning.
5172 This might help on some broken boards which
5173 machine check when some devices' config space
5174 is read. But various workarounds are disabled
5175 and some IOMMU drivers will not work.
5176 bfsort Sort PCI devices into breadth-first order.
5177 This sorting is done to get a device
5178 order compatible with older (<= 2.4) kernels.
5179 nobfsort Don't sort PCI devices into breadth-first order.
5180 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
5181 tuning and use the BIOS-configured MPS defaults.
5182 pcie_bus_safe Set every device's MPS to the largest value
5183 supported by all devices below the root complex.
5184 pcie_bus_perf Set device MPS to the largest allowable MPS
5185 based on its parent bus. Also set MRRS (Max
5186 Read Request Size) to the largest supported
5187 value (no larger than the MPS that the device
5188 or bus can support) for best performance.
5189 pcie_bus_peer2peer Set every device's MPS to 128B, which
5190 every device is guaranteed to support. This
5191 configuration allows peer-to-peer DMA between
5192 any pair of devices, possibly at the cost of
5193 reduced performance. This also guarantees
5194 that hot-added devices will work.
5195 cbiosize=nn[KMG] The fixed amount of bus space which is
5196 reserved for the CardBus bridge's IO window.
5197 The default value is 256 bytes.
5198 cbmemsize=nn[KMG] The fixed amount of bus space which is
5199 reserved for the CardBus bridge's memory
5200 window. The default value is 64 megabytes.
5201 resource_alignment=
5202 Format:
5203 [<order of align>@]<pci_dev>[; ...]
5204 Specifies alignment and device to reassign
5205 aligned memory resources. How to
5206 specify the device is described above.
5207 If <order of align> is not specified,
5208 PAGE_SIZE is used as alignment.
5209 A PCI-PCI bridge can be specified if resource
5210 windows need to be expanded.
5211 To specify the alignment for several
5212 instances of a device, the PCI vendor,
5213 device, subvendor, and subdevice may be
5214 specified, e.g., 12@pci:8086:9c22:103c:198f
5215 for 4096-byte alignment.
5216 ecrc= Enable/disable PCIe ECRC (transaction layer
5217 end-to-end CRC checking). Only effective if
5218 OS has native AER control (either granted by
5219 ACPI _OSC or forced via "pcie_ports=native")
5220 bios: Use BIOS/firmware settings. This is the
5221 the default.
5222 off: Turn ECRC off
5223 on: Turn ECRC on.
5224 hpiosize=nn[KMG] The fixed amount of bus space which is
5225 reserved for hotplug bridge's IO window.
5226 Default size is 256 bytes.
5227 hpmmiosize=nn[KMG] The fixed amount of bus space which is
5228 reserved for hotplug bridge's MMIO window.
5229 Default size is 2 megabytes.
5230 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
5231 reserved for hotplug bridge's MMIO_PREF window.
5232 Default size is 2 megabytes.
5233 hpmemsize=nn[KMG] The fixed amount of bus space which is
5234 reserved for hotplug bridge's MMIO and
5235 MMIO_PREF window.
5236 Default size is 2 megabytes.
5237 hpbussize=nn The minimum amount of additional bus numbers
5238 reserved for buses below a hotplug bridge.
5239 Default is 1.
5240 realloc= Enable/disable reallocating PCI bridge resources
5241 if allocations done by BIOS are too small to
5242 accommodate resources required by all child
5243 devices.
5244 off: Turn realloc off
5245 on: Turn realloc on
5246 realloc same as realloc=on
5247 noari do not use PCIe ARI.
5248 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
5249 do not use PCIe ATS (and IOMMU device IOTLB).
5250 pcie_scan_all Scan all possible PCIe devices. Otherwise we
5251 only look for one device below a PCIe downstream
5252 port.
5253 big_root_window Try to add a big 64bit memory window to the PCIe
5254 root complex on AMD CPUs. Some GFX hardware
5255 can resize a BAR to allow access to all VRAM.
5256 Adding the window is slightly risky (it may
5257 conflict with unreported devices), so this
5258 taints the kernel.
5259 disable_acs_redir=<pci_dev>[; ...]
5260 Specify one or more PCI devices (in the format
5261 specified above) separated by semicolons.
5262 Each device specified will have the PCI ACS
5263 redirect capabilities forced off which will
5264 allow P2P traffic between devices through
5265 bridges without forcing it upstream. Note:
5266 this removes isolation between devices and
5267 may put more devices in an IOMMU group.
5268 config_acs=
5269 Format:
5270 <ACS flags>@<pci_dev>[; ...]
5271 Specify one or more PCI devices (in the format
5272 specified above) optionally prepended with flags
5273 and separated by semicolons. The respective
5274 capabilities will be enabled, disabled or
5275 unchanged based on what is specified in
5276 flags.
5277
5278 ACS Flags is defined as follows:
5279 bit-0 : ACS Source Validation
5280 bit-1 : ACS Translation Blocking
5281 bit-2 : ACS P2P Request Redirect
5282 bit-3 : ACS P2P Completion Redirect
5283 bit-4 : ACS Upstream Forwarding
5284 bit-5 : ACS P2P Egress Control
5285 bit-6 : ACS Direct Translated P2P
5286 Each bit can be marked as:
5287 '0' – force disabled
5288 '1' – force enabled
5289 'x' – unchanged
5290 For example,
5291 pci=config_acs=10x@pci:0:0
5292 would configure all devices that support
5293 ACS to enable P2P Request Redirect, disable
5294 Translation Blocking, and leave Source
5295 Validation unchanged from whatever power-up
5296 or firmware set it to.
5297
5298 Note: this may remove isolation between devices
5299 and may put more devices in an IOMMU group.
5300 force_floating [S390] Force usage of floating interrupts.
5301 nomio [S390] Do not use MIO instructions.
5302 norid [S390] ignore the RID field and force use of
5303 one PCI domain per PCI function
5304 notph [PCIE] If the PCIE_TPH kernel config parameter
5305 is enabled, this kernel boot option can be used
5306 to disable PCIe TLP Processing Hints support
5307 system-wide.
5308
5309 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power
5310 Management.
5311 off Don't touch ASPM configuration at all. Leave any
5312 configuration done by firmware unchanged.
5313 force Enable ASPM even on devices that claim not to support it.
5314 WARNING: Forcing ASPM on may cause system lockups.
5315
5316 pcie_ports= [PCIE] PCIe port services handling:
5317 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
5318 even if the platform doesn't give the OS permission to
5319 use them. This may cause conflicts if the platform
5320 also tries to use these services.
5321 dpc-native Use native PCIe service for DPC only. May
5322 cause conflicts if firmware uses AER or DPC.
5323 compat Disable native PCIe services (PME, AER, DPC, PCIe
5324 hotplug).
5325
5326 pcie_port_pm= [PCIE] PCIe port power management handling:
5327 off Disable power management of all PCIe ports
5328 force Forcibly enable power management of all PCIe ports
5329
5330 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
5331 nomsi Do not use MSI for native PCIe PME signaling (this makes
5332 all PCIe root ports use INTx for all services).
5333
5334 pcmv= [HW,PCMCIA] BadgePAD 4
5335
5336 pd_ignore_unused
5337 [PM]
5338 Keep all power-domains already enabled by bootloader on,
5339 even if no driver has claimed them. This is useful
5340 for debug and development, but should not be
5341 needed on a platform with proper driver support.
5342
5343 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
5344 boot time.
5345 Format: { 0 | 1 }
5346 See arch/parisc/kernel/pdc_chassis.c
5347
5348 percpu_alloc= [MM,EARLY]
5349 Select which percpu first chunk allocator to use.
5350 Currently supported values are "embed" and "page".
5351 Archs may support subset or none of the selections.
5352 See comments in mm/percpu.c for details on each
5353 allocator. This parameter is primarily for debugging
5354 and performance comparison.
5355
5356 pirq= [SMP,APIC] Manual mp-table setup
5357 See Documentation/arch/x86/i386/IO-APIC.rst.
5358
5359 plip= [PPT,NET] Parallel port network link
5360 Format: { parport<nr> | timid | 0 }
5361 See also Documentation/admin-guide/parport.rst.
5362
5363 pmtmr= [X86] Manual setup of pmtmr I/O Port.
5364 Override pmtimer IOPort with a hex value.
5365 e.g. pmtmr=0x508
5366
5367 pmu_override= [PPC] Override the PMU.
5368 This option takes over the PMU facility, so it is no
5369 longer usable by perf. Setting this option starts the
5370 PMU counters by setting MMCR0 to 0 (the FC bit is
5371 cleared). If a number is given, then MMCR1 is set to
5372 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
5373 remains 0.
5374
5375 pm_async= [PM]
5376 Format: off
5377 This parameter sets the initial value of the
5378 /sys/power/pm_async sysfs knob at boot time.
5379 If set to "off", disables asynchronous suspend and
5380 resume of devices during system-wide power transitions.
5381 This can be useful on platforms where device
5382 dependencies are not well-defined, or for debugging
5383 power management issues. Asynchronous operations are
5384 enabled by default.
5385
5386
5387 pm_debug_messages [SUSPEND,KNL]
5388 Enable suspend/resume debug messages during boot up.
5389
5390 pnp.debug=1 [PNP]
5391 Enable PNP debug messages (depends on the
5392 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
5393 via /sys/module/pnp/parameters/debug. We always show
5394 current resource usage; turning this on also shows
5395 possible settings and some assignment information.
5396
5397 pnpacpi= [ACPI]
5398 { off }
5399
5400 pnpbios= [ISAPNP]
5401 { on | off | curr | res | no-curr | no-res }
5402
5403 pnp_reserve_irq=
5404 [ISAPNP] Exclude IRQs for the autoconfiguration
5405
5406 pnp_reserve_dma=
5407 [ISAPNP] Exclude DMAs for the autoconfiguration
5408
5409 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
5410 Ranges are in pairs (I/O port base and size).
5411
5412 pnp_reserve_mem=
5413 [ISAPNP] Exclude memory regions for the
5414 autoconfiguration.
5415 Ranges are in pairs (memory base and size).
5416
5417 ports= [IP_VS_FTP] IPVS ftp helper module
5418 Default is 21.
5419 Up to 8 (IP_VS_APP_MAX_PORTS) ports
5420 may be specified.
5421 Format: <port>,<port>....
5422
5423 possible_cpus= [SMP,S390,X86]
5424 Format: <unsigned int>
5425 Set the number of possible CPUs, overriding the
5426 regular discovery mechanisms (such as ACPI/FW, etc).
5427
5428 powersave=off [PPC] This option disables power saving features.
5429 It specifically disables cpuidle and sets the
5430 platform machine description specific power_save
5431 function to NULL. On Idle the CPU just reduces
5432 execution priority.
5433
5434 ppc_strict_facility_enable
5435 [PPC,ENABLE] This option catches any kernel floating point,
5436 Altivec, VSX and SPE outside of regions specifically
5437 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
5438 There is some performance impact when enabling this.
5439
5440 ppc_tm= [PPC,EARLY]
5441 Format: {"off"}
5442 Disable Hardware Transactional Memory
5443
5444 preempt= [KNL]
5445 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
5446 none - Limited to cond_resched() calls
5447 voluntary - Limited to cond_resched() and might_sleep() calls
5448 full - Any section that isn't explicitly preempt disabled
5449 can be preempted anytime. Tasks will also yield
5450 contended spinlocks (if the critical section isn't
5451 explicitly preempt disabled beyond the lock itself).
5452 lazy - Scheduler controlled. Similar to full but instead
5453 of preempting the task immediately, the task gets
5454 one HZ tick time to yield itself before the
5455 preemption will be forced. One preemption is when the
5456 task returns to user space.
5457
5458 print-fatal-signals=
5459 [KNL] debug: print fatal signals
5460
5461 If enabled, warn about various signal handling
5462 related application anomalies: too many signals,
5463 too many POSIX.1 timers, fatal signals causing a
5464 coredump - etc.
5465
5466 If you hit the warning due to signal overflow,
5467 you might want to try "ulimit -i unlimited".
5468
5469 default: off.
5470
5471 printk.always_kmsg_dump=
5472 Trigger kmsg_dump for cases other than kernel oops or
5473 panics
5474 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
5475 default: disabled
5476
5477 printk.console_no_auto_verbose=
5478 Disable console loglevel raise on oops, panic
5479 or lockdep-detected issues (only if lock debug is on).
5480 With an exception to setups with low baudrate on
5481 serial console, keeping this 0 is a good choice
5482 in order to provide more debug information.
5483 Format: <bool>
5484 default: 0 (auto_verbose is enabled)
5485
5486 printk.debug_non_panic_cpus=
5487 Allows storing messages from non-panic CPUs into
5488 the printk log buffer during panic(). They are
5489 flushed to consoles by the panic-CPU on
5490 a best-effort basis.
5491 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
5492 Default: disabled
5493
5494 printk.devkmsg={on,off,ratelimit}
5495 Control writing to /dev/kmsg.
5496 on - unlimited logging to /dev/kmsg from userspace
5497 off - logging to /dev/kmsg disabled
5498 ratelimit - ratelimit the logging
5499 Default: ratelimit
5500
5501 printk.time= Show timing data prefixed to each printk message line
5502 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
5503
5504 proc_mem.force_override= [KNL]
5505 Format: {always | ptrace | never}
5506 Traditionally /proc/pid/mem allows memory permissions to be
5507 overridden without restrictions. This option may be set to
5508 restrict that. Can be one of:
5509 - 'always': traditional behavior always allows mem overrides.
5510 - 'ptrace': only allow mem overrides for active ptracers.
5511 - 'never': never allow mem overrides.
5512 If not specified, default is the CONFIG_PROC_MEM_* choice.
5513
5514 processor.max_cstate= [HW,ACPI]
5515 Limit processor to maximum C-state
5516 max_cstate=9 overrides any DMI blacklist limit.
5517
5518 processor.nocst [HW,ACPI]
5519 Ignore the _CST method to determine C-states,
5520 instead using the legacy FADT method
5521
5522 profile= [KNL] Enable kernel profiling via /proc/profile
5523 Format: [<profiletype>,]<number>
5524 Param: <profiletype>: "schedule" or "kvm"
5525 [defaults to kernel profiling]
5526 Param: "schedule" - profile schedule points.
5527 Param: "kvm" - profile VM exits.
5528 Param: <number> - step/bucket size as a power of 2 for
5529 statistical time based profiling.
5530
5531 prot_virt= [S390] enable hosting protected virtual machines
5532 isolated from the hypervisor (if hardware supports
5533 that). If enabled, the default kernel base address
5534 might be overridden even when Kernel Address Space
5535 Layout Randomization is disabled.
5536 Format: <bool>
5537
5538 psi= [KNL] Enable or disable pressure stall information
5539 tracking.
5540 Format: <bool>
5541
5542 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
5543 probe for; one of (bare|imps|exps|lifebook|any).
5544 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
5545 per second.
5546 psmouse.resetafter= [HW,MOUSE]
5547 Try to reset the device after so many bad packets
5548 (0 = never).
5549 psmouse.resolution=
5550 [HW,MOUSE] Set desired mouse resolution, in dpi.
5551 psmouse.smartscroll=
5552 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
5553 0 = disabled, 1 = enabled (default).
5554
5555 pstore.backend= Specify the name of the pstore backend to use
5556
5557 pti= [X86-64] Control Page Table Isolation of user and
5558 kernel address spaces. Disabling this feature
5559 removes hardening, but improves performance of
5560 system calls and interrupts.
5561
5562 on - unconditionally enable
5563 off - unconditionally disable
5564 auto - kernel detects whether your CPU model is
5565 vulnerable to issues that PTI mitigates
5566
5567 Not specifying this option is equivalent to pti=auto.
5568
5569 pty.legacy_count=
5570 [KNL] Number of legacy pty's. Overwrites compiled-in
5571 default number.
5572
5573 quiet [KNL,EARLY] Disable most log messages
5574
5575 r128= [HW,DRM]
5576
5577 radix_hcall_invalidate=on [PPC/PSERIES]
5578 Disable RADIX GTSE feature and use hcall for TLB
5579 invalidate.
5580
5581 raid= [HW,RAID]
5582 See Documentation/admin-guide/md.rst.
5583
5584 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
5585 See Documentation/admin-guide/blockdev/ramdisk.rst.
5586
5587 ramdisk_start= [Deprecated,RAM] RAM disk image start address
5588
5589 random.trust_cpu=off
5590 [KNL,EARLY] Disable trusting the use of the CPU's
5591 random number generator (if available) to
5592 initialize the kernel's RNG.
5593
5594 random.trust_bootloader=off
5595 [KNL,EARLY] Disable trusting the use of the a seed
5596 passed by the bootloader (if available) to
5597 initialize the kernel's RNG.
5598
5599 randomize_kstack_offset=
5600 [KNL,EARLY] Enable or disable kernel stack offset
5601 randomization, which provides roughly 5 bits of
5602 entropy, frustrating memory corruption attacks
5603 that depend on stack address determinism or
5604 cross-syscall address exposures. This is only
5605 available on architectures that have defined
5606 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
5607 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
5608 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
5609
5610 ras=option[,option,...] [KNL] RAS-specific options
5611
5612 cec_disable [X86]
5613 Disable the Correctable Errors Collector,
5614 see CONFIG_RAS_CEC help text.
5615
5616 rcu_nocbs[=cpu-list]
5617 [KNL] The optional argument is a cpu list,
5618 as described above.
5619
5620 In kernels built with CONFIG_RCU_NOCB_CPU=y,
5621 enable the no-callback CPU mode, which prevents
5622 such CPUs' callbacks from being invoked in
5623 softirq context. Invocation of such CPUs' RCU
5624 callbacks will instead be offloaded to "rcuox/N"
5625 kthreads created for that purpose, where "x" is
5626 "p" for RCU-preempt, "s" for RCU-sched, and "g"
5627 for the kthreads that mediate grace periods; and
5628 "N" is the CPU number. This reduces OS jitter on
5629 the offloaded CPUs, which can be useful for HPC
5630 and real-time workloads. It can also improve
5631 energy efficiency for asymmetric multiprocessors.
5632
5633 If a cpulist is passed as an argument, the specified
5634 list of CPUs is set to no-callback mode from boot.
5635
5636 Otherwise, if the '=' sign and the cpulist
5637 arguments are omitted, no CPU will be set to
5638 no-callback mode from boot but the mode may be
5639 toggled at runtime via cpusets.
5640
5641 Note that this argument takes precedence over
5642 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
5643
5644 rcu_nocb_poll [KNL]
5645 Rather than requiring that offloaded CPUs
5646 (specified by rcu_nocbs= above) explicitly
5647 awaken the corresponding "rcuoN" kthreads,
5648 make these kthreads poll for callbacks.
5649 This improves the real-time response for the
5650 offloaded CPUs by relieving them of the need to
5651 wake up the corresponding kthread, but degrades
5652 energy efficiency by requiring that the kthreads
5653 periodically wake up to do the polling.
5654
5655 rcutree.blimit= [KNL]
5656 Set maximum number of finished RCU callbacks to
5657 process in one batch.
5658
5659 rcutree.csd_lock_suppress_rcu_stall= [KNL]
5660 Do only a one-line RCU CPU stall warning when
5661 there is an ongoing too-long CSD-lock wait.
5662
5663 rcutree.do_rcu_barrier= [KNL]
5664 Request a call to rcu_barrier(). This is
5665 throttled so that userspace tests can safely
5666 hammer on the sysfs variable if they so choose.
5667 If triggered before the RCU grace-period machinery
5668 is fully active, this will error out with EAGAIN.
5669
5670 rcutree.dump_tree= [KNL]
5671 Dump the structure of the rcu_node combining tree
5672 out at early boot. This is used for diagnostic
5673 purposes, to verify correct tree setup.
5674
5675 rcutree.gp_cleanup_delay= [KNL]
5676 Set the number of jiffies to delay each step of
5677 RCU grace-period cleanup.
5678
5679 rcutree.gp_init_delay= [KNL]
5680 Set the number of jiffies to delay each step of
5681 RCU grace-period initialization.
5682
5683 rcutree.gp_preinit_delay= [KNL]
5684 Set the number of jiffies to delay each step of
5685 RCU grace-period pre-initialization, that is,
5686 the propagation of recent CPU-hotplug changes up
5687 the rcu_node combining tree.
5688
5689 rcutree.jiffies_till_first_fqs= [KNL]
5690 Set delay from grace-period initialization to
5691 first attempt to force quiescent states.
5692 Units are jiffies, minimum value is zero,
5693 and maximum value is HZ.
5694
5695 rcutree.jiffies_till_next_fqs= [KNL]
5696 Set delay between subsequent attempts to force
5697 quiescent states. Units are jiffies, minimum
5698 value is one, and maximum value is HZ.
5699
5700 rcutree.jiffies_till_sched_qs= [KNL]
5701 Set required age in jiffies for a
5702 given grace period before RCU starts
5703 soliciting quiescent-state help from
5704 rcu_note_context_switch() and cond_resched().
5705 If not specified, the kernel will calculate
5706 a value based on the most recent settings
5707 of rcutree.jiffies_till_first_fqs
5708 and rcutree.jiffies_till_next_fqs.
5709 This calculated value may be viewed in
5710 rcutree.jiffies_to_sched_qs. Any attempt to set
5711 rcutree.jiffies_to_sched_qs will be cheerfully
5712 overwritten.
5713
5714 rcutree.kthread_prio= [KNL,BOOT]
5715 Set the SCHED_FIFO priority of the RCU per-CPU
5716 kthreads (rcuc/N). This value is also used for
5717 the priority of the RCU boost threads (rcub/N)
5718 and for the RCU grace-period kthreads (rcu_bh,
5719 rcu_preempt, and rcu_sched). If RCU_BOOST is
5720 set, valid values are 1-99 and the default is 1
5721 (the least-favored priority). Otherwise, when
5722 RCU_BOOST is not set, valid values are 0-99 and
5723 the default is zero (non-realtime operation).
5724 When RCU_NOCB_CPU is set, also adjust the
5725 priority of NOCB callback kthreads.
5726
5727 rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
5728 On callback-offloaded (rcu_nocbs) CPUs,
5729 RCU reduces the lock contention that would
5730 otherwise be caused by callback floods through
5731 use of the ->nocb_bypass list. However, in the
5732 common non-flooded case, RCU queues directly to
5733 the main ->cblist in order to avoid the extra
5734 overhead of the ->nocb_bypass list and its lock.
5735 But if there are too many callbacks queued during
5736 a single jiffy, RCU pre-queues the callbacks into
5737 the ->nocb_bypass queue. The definition of "too
5738 many" is supplied by this kernel boot parameter.
5739
5740 rcutree.nohz_full_patience_delay= [KNL]
5741 On callback-offloaded (rcu_nocbs) CPUs, avoid
5742 disturbing RCU unless the grace period has
5743 reached the specified age in milliseconds.
5744 Defaults to zero. Large values will be capped
5745 at five seconds. All values will be rounded down
5746 to the nearest value representable by jiffies.
5747
5748 rcutree.qhimark= [KNL]
5749 Set threshold of queued RCU callbacks beyond which
5750 batch limiting is disabled.
5751
5752 rcutree.qlowmark= [KNL]
5753 Set threshold of queued RCU callbacks below which
5754 batch limiting is re-enabled.
5755
5756 rcutree.qovld= [KNL]
5757 Set threshold of queued RCU callbacks beyond which
5758 RCU's force-quiescent-state scan will aggressively
5759 enlist help from cond_resched() and sched IPIs to
5760 help CPUs more quickly reach quiescent states.
5761 Set to less than zero to make this be set based
5762 on rcutree.qhimark at boot time and to zero to
5763 disable more aggressive help enlistment.
5764
5765 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
5766 Set the page-cache refill delay (in milliseconds)
5767 in response to low-memory conditions. The range
5768 of permitted values is in the range 0:100000.
5769
5770 rcutree.rcu_divisor= [KNL]
5771 Set the shift-right count to use to compute
5772 the callback-invocation batch limit bl from
5773 the number of callbacks queued on this CPU.
5774 The result will be bounded below by the value of
5775 the rcutree.blimit kernel parameter. Every bl
5776 callbacks, the softirq handler will exit in
5777 order to allow the CPU to do other work.
5778
5779 Please note that this callback-invocation batch
5780 limit applies only to non-offloaded callback
5781 invocation. Offloaded callbacks are instead
5782 invoked in the context of an rcuoc kthread, which
5783 scheduler will preempt as it does any other task.
5784
5785 rcutree.rcu_fanout_exact= [KNL]
5786 Disable autobalancing of the rcu_node combining
5787 tree. This is used by rcutorture, and might
5788 possibly be useful for architectures having high
5789 cache-to-cache transfer latencies.
5790
5791 rcutree.rcu_fanout_leaf= [KNL]
5792 Change the number of CPUs assigned to each
5793 leaf rcu_node structure. Useful for very
5794 large systems, which will choose the value 64,
5795 and for NUMA systems with large remote-access
5796 latencies, which will choose a value aligned
5797 with the appropriate hardware boundaries.
5798
5799 rcutree.rcu_min_cached_objs= [KNL]
5800 Minimum number of objects which are cached and
5801 maintained per one CPU. Object size is equal
5802 to PAGE_SIZE. The cache allows to reduce the
5803 pressure to page allocator, also it makes the
5804 whole algorithm to behave better in low memory
5805 condition.
5806
5807 rcutree.rcu_nocb_gp_stride= [KNL]
5808 Set the number of NOCB callback kthreads in
5809 each group, which defaults to the square root
5810 of the number of CPUs. Larger numbers reduce
5811 the wakeup overhead on the global grace-period
5812 kthread, but increases that same overhead on
5813 each group's NOCB grace-period kthread.
5814
5815 rcutree.rcu_kick_kthreads= [KNL]
5816 Cause the grace-period kthread to get an extra
5817 wake_up() if it sleeps three times longer than
5818 it should at force-quiescent-state time.
5819 This wake_up() will be accompanied by a
5820 WARN_ONCE() splat and an ftrace_dump().
5821
5822 rcutree.rcu_resched_ns= [KNL]
5823 Limit the time spend invoking a batch of RCU
5824 callbacks to the specified number of nanoseconds.
5825 By default, this limit is checked only once
5826 every 32 callbacks in order to limit the pain
5827 inflicted by local_clock() overhead.
5828
5829 rcutree.rcu_unlock_delay= [KNL]
5830 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
5831 this specifies an rcu_read_unlock()-time delay
5832 in microseconds. This defaults to zero.
5833 Larger delays increase the probability of
5834 catching RCU pointer leaks, that is, buggy use
5835 of RCU-protected pointers after the relevant
5836 rcu_read_unlock() has completed.
5837
5838 rcutree.sysrq_rcu= [KNL]
5839 Commandeer a sysrq key to dump out Tree RCU's
5840 rcu_node tree with an eye towards determining
5841 why a new grace period has not yet started.
5842
5843 rcutree.use_softirq= [KNL]
5844 If set to zero, move all RCU_SOFTIRQ processing to
5845 per-CPU rcuc kthreads. Defaults to a non-zero
5846 value, meaning that RCU_SOFTIRQ is used by default.
5847 Specify rcutree.use_softirq=0 to use rcuc kthreads.
5848
5849 But note that CONFIG_PREEMPT_RT=y kernels disable
5850 this kernel boot parameter, forcibly setting it
5851 to zero.
5852
5853 rcutree.enable_rcu_lazy= [KNL]
5854 To save power, batch RCU callbacks and flush after
5855 delay, memory pressure or callback list growing too
5856 big.
5857
5858 rcutree.rcu_normal_wake_from_gp= [KNL]
5859 Reduces a latency of synchronize_rcu() call. This approach
5860 maintains its own track of synchronize_rcu() callers, so it
5861 does not interact with regular callbacks because it does not
5862 use a call_rcu[_hurry]() path. Please note, this is for a
5863 normal grace period.
5864
5865 How to enable it:
5866
5867 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp
5868 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1"
5869
5870 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly
5871 disabled by the boot parameter passing 0.
5872
5873 rcuscale.gp_async= [KNL]
5874 Measure performance of asynchronous
5875 grace-period primitives such as call_rcu().
5876
5877 rcuscale.gp_async_max= [KNL]
5878 Specify the maximum number of outstanding
5879 callbacks per writer thread. When a writer
5880 thread exceeds this limit, it invokes the
5881 corresponding flavor of rcu_barrier() to allow
5882 previously posted callbacks to drain.
5883
5884 rcuscale.gp_exp= [KNL]
5885 Measure performance of expedited synchronous
5886 grace-period primitives.
5887
5888 rcuscale.holdoff= [KNL]
5889 Set test-start holdoff period. The purpose of
5890 this parameter is to delay the start of the
5891 test until boot completes in order to avoid
5892 interference.
5893
5894 rcuscale.kfree_by_call_rcu= [KNL]
5895 In kernels built with CONFIG_RCU_LAZY=y, test
5896 call_rcu() instead of kfree_rcu().
5897
5898 rcuscale.kfree_mult= [KNL]
5899 Instead of allocating an object of size kfree_obj,
5900 allocate one of kfree_mult * sizeof(kfree_obj).
5901 Defaults to 1.
5902
5903 rcuscale.kfree_rcu_test= [KNL]
5904 Set to measure performance of kfree_rcu() flooding.
5905
5906 rcuscale.kfree_rcu_test_double= [KNL]
5907 Test the double-argument variant of kfree_rcu().
5908 If this parameter has the same value as
5909 rcuscale.kfree_rcu_test_single, both the single-
5910 and double-argument variants are tested.
5911
5912 rcuscale.kfree_rcu_test_single= [KNL]
5913 Test the single-argument variant of kfree_rcu().
5914 If this parameter has the same value as
5915 rcuscale.kfree_rcu_test_double, both the single-
5916 and double-argument variants are tested.
5917
5918 rcuscale.kfree_nthreads= [KNL]
5919 The number of threads running loops of kfree_rcu().
5920
5921 rcuscale.kfree_alloc_num= [KNL]
5922 Number of allocations and frees done in an iteration.
5923
5924 rcuscale.kfree_loops= [KNL]
5925 Number of loops doing rcuscale.kfree_alloc_num number
5926 of allocations and frees.
5927
5928 rcuscale.minruntime= [KNL]
5929 Set the minimum test run time in seconds. This
5930 does not affect the data-collection interval,
5931 but instead allows better measurement of things
5932 like CPU consumption.
5933
5934 rcuscale.nreaders= [KNL]
5935 Set number of RCU readers. The value -1 selects
5936 N, where N is the number of CPUs. A value
5937 "n" less than -1 selects N-n+1, where N is again
5938 the number of CPUs. For example, -2 selects N
5939 (the number of CPUs), -3 selects N+1, and so on.
5940 A value of "n" less than or equal to -N selects
5941 a single reader.
5942
5943 rcuscale.nwriters= [KNL]
5944 Set number of RCU writers. The values operate
5945 the same as for rcuscale.nreaders.
5946 N, where N is the number of CPUs
5947
5948 rcuscale.scale_type= [KNL]
5949 Specify the RCU implementation to test.
5950
5951 rcuscale.shutdown= [KNL]
5952 Shut the system down after performance tests
5953 complete. This is useful for hands-off automated
5954 testing.
5955
5956 rcuscale.verbose= [KNL]
5957 Enable additional printk() statements.
5958
5959 rcuscale.writer_holdoff= [KNL]
5960 Write-side holdoff between grace periods,
5961 in microseconds. The default of zero says
5962 no holdoff.
5963
5964 rcuscale.writer_holdoff_jiffies= [KNL]
5965 Additional write-side holdoff between grace
5966 periods, but in jiffies. The default of zero
5967 says no holdoff.
5968
5969 rcutorture.fqs_duration= [KNL]
5970 Set duration of force_quiescent_state bursts
5971 in microseconds.
5972
5973 rcutorture.fqs_holdoff= [KNL]
5974 Set holdoff time within force_quiescent_state bursts
5975 in microseconds.
5976
5977 rcutorture.fqs_stutter= [KNL]
5978 Set wait time between force_quiescent_state bursts
5979 in seconds.
5980
5981 rcutorture.fwd_progress= [KNL]
5982 Specifies the number of kthreads to be used
5983 for RCU grace-period forward-progress testing
5984 for the types of RCU supporting this notion.
5985 Defaults to 1 kthread, values less than zero or
5986 greater than the number of CPUs cause the number
5987 of CPUs to be used.
5988
5989 rcutorture.fwd_progress_div= [KNL]
5990 Specify the fraction of a CPU-stall-warning
5991 period to do tight-loop forward-progress testing.
5992
5993 rcutorture.fwd_progress_holdoff= [KNL]
5994 Number of seconds to wait between successive
5995 forward-progress tests.
5996
5997 rcutorture.fwd_progress_need_resched= [KNL]
5998 Enclose cond_resched() calls within checks for
5999 need_resched() during tight-loop forward-progress
6000 testing.
6001
6002 rcutorture.gp_cond= [KNL]
6003 Use conditional/asynchronous update-side
6004 normal-grace-period primitives, if available.
6005
6006 rcutorture.gp_cond_exp= [KNL]
6007 Use conditional/asynchronous update-side
6008 expedited-grace-period primitives, if available.
6009
6010 rcutorture.gp_cond_full= [KNL]
6011 Use conditional/asynchronous update-side
6012 normal-grace-period primitives that also take
6013 concurrent expedited grace periods into account,
6014 if available.
6015
6016 rcutorture.gp_cond_exp_full= [KNL]
6017 Use conditional/asynchronous update-side
6018 expedited-grace-period primitives that also take
6019 concurrent normal grace periods into account,
6020 if available.
6021
6022 rcutorture.gp_cond_wi= [KNL]
6023 Nominal wait interval for normal conditional
6024 grace periods (specified by rcutorture's
6025 gp_cond and gp_cond_full module parameters),
6026 in microseconds. The actual wait interval will
6027 be randomly selected to nanosecond granularity up
6028 to this wait interval. Defaults to 16 jiffies,
6029 for example, 16,000 microseconds on a system
6030 with HZ=1000.
6031
6032 rcutorture.gp_cond_wi_exp= [KNL]
6033 Nominal wait interval for expedited conditional
6034 grace periods (specified by rcutorture's
6035 gp_cond_exp and gp_cond_exp_full module
6036 parameters), in microseconds. The actual wait
6037 interval will be randomly selected to nanosecond
6038 granularity up to this wait interval. Defaults to
6039 128 microseconds.
6040
6041 rcutorture.gp_exp= [KNL]
6042 Use expedited update-side primitives, if available.
6043
6044 rcutorture.gp_normal= [KNL]
6045 Use normal (non-expedited) asynchronous
6046 update-side primitives, if available.
6047
6048 rcutorture.gp_poll= [KNL]
6049 Use polled update-side normal-grace-period
6050 primitives, if available.
6051
6052 rcutorture.gp_poll_exp= [KNL]
6053 Use polled update-side expedited-grace-period
6054 primitives, if available.
6055
6056 rcutorture.gp_poll_full= [KNL]
6057 Use polled update-side normal-grace-period
6058 primitives that also take concurrent expedited
6059 grace periods into account, if available.
6060
6061 rcutorture.gp_poll_exp_full= [KNL]
6062 Use polled update-side expedited-grace-period
6063 primitives that also take concurrent normal
6064 grace periods into account, if available.
6065
6066 rcutorture.gp_poll_wi= [KNL]
6067 Nominal wait interval for normal conditional
6068 grace periods (specified by rcutorture's
6069 gp_poll and gp_poll_full module parameters),
6070 in microseconds. The actual wait interval will
6071 be randomly selected to nanosecond granularity up
6072 to this wait interval. Defaults to 16 jiffies,
6073 for example, 16,000 microseconds on a system
6074 with HZ=1000.
6075
6076 rcutorture.gp_poll_wi_exp= [KNL]
6077 Nominal wait interval for expedited conditional
6078 grace periods (specified by rcutorture's
6079 gp_poll_exp and gp_poll_exp_full module
6080 parameters), in microseconds. The actual wait
6081 interval will be randomly selected to nanosecond
6082 granularity up to this wait interval. Defaults to
6083 128 microseconds.
6084
6085 rcutorture.gp_sync= [KNL]
6086 Use normal (non-expedited) synchronous
6087 update-side primitives, if available. If all
6088 of rcutorture.gp_cond=, rcutorture.gp_exp=,
6089 rcutorture.gp_normal=, and rcutorture.gp_sync=
6090 are zero, rcutorture acts as if is interpreted
6091 they are all non-zero.
6092
6093 rcutorture.gpwrap_lag= [KNL]
6094 Enable grace-period wrap lag testing. Setting
6095 to false prevents the gpwrap lag test from
6096 running. Default is true.
6097
6098 rcutorture.gpwrap_lag_gps= [KNL]
6099 Set the value for grace-period wrap lag during
6100 active lag testing periods. This controls how many
6101 grace periods differences we tolerate between
6102 rdp and rnp's gp_seq before setting overflow flag.
6103 The default is always set to 8.
6104
6105 rcutorture.gpwrap_lag_cycle_mins= [KNL]
6106 Set the total cycle duration for gpwrap lag
6107 testing in minutes. This is the total time for
6108 one complete cycle of active and inactive
6109 testing periods. Default is 30 minutes.
6110
6111 rcutorture.gpwrap_lag_active_mins= [KNL]
6112 Set the duration for which gpwrap lag is active
6113 within each cycle, in minutes. During this time,
6114 the grace-period wrap lag will be set to the
6115 value specified by gpwrap_lag_gps. Default is
6116 5 minutes.
6117
6118 rcutorture.irqreader= [KNL]
6119 Run RCU readers from irq handlers, or, more
6120 accurately, from a timer handler. Not all RCU
6121 flavors take kindly to this sort of thing.
6122
6123 rcutorture.leakpointer= [KNL]
6124 Leak an RCU-protected pointer out of the reader.
6125 This can of course result in splats, and is
6126 intended to test the ability of things like
6127 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
6128 such leaks.
6129
6130 rcutorture.n_barrier_cbs= [KNL]
6131 Set callbacks/threads for rcu_barrier() testing.
6132
6133 rcutorture.nfakewriters= [KNL]
6134 Set number of concurrent RCU writers. These just
6135 stress RCU, they don't participate in the actual
6136 test, hence the "fake".
6137
6138 rcutorture.nocbs_nthreads= [KNL]
6139 Set number of RCU callback-offload togglers.
6140 Zero (the default) disables toggling.
6141
6142 rcutorture.nocbs_toggle= [KNL]
6143 Set the delay in milliseconds between successive
6144 callback-offload toggling attempts.
6145
6146 rcutorture.nreaders= [KNL]
6147 Set number of RCU readers. The value -1 selects
6148 N-1, where N is the number of CPUs. A value
6149 "n" less than -1 selects N-n-2, where N is again
6150 the number of CPUs. For example, -2 selects N
6151 (the number of CPUs), -3 selects N+1, and so on.
6152
6153 rcutorture.object_debug= [KNL]
6154 Enable debug-object double-call_rcu() testing.
6155
6156 rcutorture.onoff_holdoff= [KNL]
6157 Set time (s) after boot for CPU-hotplug testing.
6158
6159 rcutorture.onoff_interval= [KNL]
6160 Set time (jiffies) between CPU-hotplug operations,
6161 or zero to disable CPU-hotplug testing.
6162
6163 rcutorture.preempt_duration= [KNL]
6164 Set duration (in milliseconds) of preemptions
6165 by a high-priority FIFO real-time task. Set to
6166 zero (the default) to disable. The CPUs to
6167 preempt are selected randomly from the set that
6168 are online at a given point in time. Races with
6169 CPUs going offline are ignored, with that attempt
6170 at preemption skipped.
6171
6172 rcutorture.preempt_interval= [KNL]
6173 Set interval (in milliseconds, defaulting to one
6174 second) between preemptions by a high-priority
6175 FIFO real-time task. This delay is mediated
6176 by an hrtimer and is further fuzzed to avoid
6177 inadvertent synchronizations.
6178
6179 rcutorture.read_exit_burst= [KNL]
6180 The number of times in a given read-then-exit
6181 episode that a set of read-then-exit kthreads
6182 is spawned.
6183
6184 rcutorture.read_exit_delay= [KNL]
6185 The delay, in seconds, between successive
6186 read-then-exit testing episodes.
6187
6188 rcutorture.reader_flavor= [KNL]
6189 A bit mask indicating which readers to use.
6190 If there is more than one bit set, the readers
6191 are entered from low-order bit up, and are
6192 exited in the opposite order. For SRCU, the
6193 0x1 bit is normal readers, 0x2 NMI-safe readers,
6194 and 0x4 light-weight readers.
6195
6196 rcutorture.shuffle_interval= [KNL]
6197 Set task-shuffle interval (s). Shuffling tasks
6198 allows some CPUs to go into dyntick-idle mode
6199 during the rcutorture test.
6200
6201 rcutorture.shutdown_secs= [KNL]
6202 Set time (s) after boot system shutdown. This
6203 is useful for hands-off automated testing.
6204
6205 rcutorture.stall_cpu= [KNL]
6206 Duration of CPU stall (s) to test RCU CPU stall
6207 warnings, zero to disable.
6208
6209 rcutorture.stall_cpu_block= [KNL]
6210 Sleep while stalling if set. This will result
6211 in warnings from preemptible RCU in addition to
6212 any other stall-related activity. Note that
6213 in kernels built with CONFIG_PREEMPTION=n and
6214 CONFIG_PREEMPT_COUNT=y, this parameter will
6215 cause the CPU to pass through a quiescent state.
6216 Given CONFIG_PREEMPTION=n, this will suppress
6217 RCU CPU stall warnings, but will instead result
6218 in scheduling-while-atomic splats.
6219
6220 Use of this module parameter results in splats.
6221
6222
6223 rcutorture.stall_cpu_holdoff= [KNL]
6224 Time to wait (s) after boot before inducing stall.
6225
6226 rcutorture.stall_cpu_irqsoff= [KNL]
6227 Disable interrupts while stalling if set, but only
6228 on the first stall in the set.
6229
6230 rcutorture.stall_cpu_repeat= [KNL]
6231 Number of times to repeat the stall sequence,
6232 so that rcutorture.stall_cpu_repeat=3 will result
6233 in four stall sequences.
6234
6235 rcutorture.stall_gp_kthread= [KNL]
6236 Duration (s) of forced sleep within RCU
6237 grace-period kthread to test RCU CPU stall
6238 warnings, zero to disable. If both stall_cpu
6239 and stall_gp_kthread are specified, the
6240 kthread is starved first, then the CPU.
6241
6242 rcutorture.stat_interval= [KNL]
6243 Time (s) between statistics printk()s.
6244
6245 rcutorture.stutter= [KNL]
6246 Time (s) to stutter testing, for example, specifying
6247 five seconds causes the test to run for five seconds,
6248 wait for five seconds, and so on. This tests RCU's
6249 ability to transition abruptly to and from idle.
6250
6251 rcutorture.test_boost= [KNL]
6252 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
6253 "Maybe" means test if the RCU implementation
6254 under test support RCU priority boosting.
6255
6256 rcutorture.test_boost_duration= [KNL]
6257 Duration (s) of each individual boost test.
6258
6259 rcutorture.test_boost_holdoff= [KNL]
6260 Holdoff time (s) from start of test to the start
6261 of RCU priority-boost testing. Defaults to zero,
6262 that is, no holdoff.
6263
6264 rcutorture.test_boost_interval= [KNL]
6265 Interval (s) between each boost test.
6266
6267 rcutorture.test_no_idle_hz= [KNL]
6268 Test RCU's dyntick-idle handling. See also the
6269 rcutorture.shuffle_interval parameter.
6270
6271 rcutorture.torture_type= [KNL]
6272 Specify the RCU implementation to test.
6273
6274 rcutorture.verbose= [KNL]
6275 Enable additional printk() statements.
6276
6277 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
6278 Dump ftrace buffer after reporting RCU CPU
6279 stall warning.
6280
6281 rcupdate.rcu_cpu_stall_notifiers= [KNL]
6282 Provide RCU CPU stall notifiers, but see the
6283 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig
6284 option's help text. TL;DR: You almost certainly
6285 do not want rcupdate.rcu_cpu_stall_notifiers.
6286
6287 rcupdate.rcu_cpu_stall_suppress= [KNL]
6288 Suppress RCU CPU stall warning messages.
6289
6290 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
6291 Suppress RCU CPU stall warning messages and
6292 rcutorture writer stall warnings that occur
6293 during early boot, that is, during the time
6294 before the init task is spawned.
6295
6296 rcupdate.rcu_cpu_stall_timeout= [KNL]
6297 Set timeout for RCU CPU stall warning messages.
6298 The value is in seconds and the maximum allowed
6299 value is 300 seconds.
6300
6301 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
6302 Set timeout for expedited RCU CPU stall warning
6303 messages. The value is in milliseconds
6304 and the maximum allowed value is 21000
6305 milliseconds. Please note that this value is
6306 adjusted to an arch timer tick resolution.
6307 Setting this to zero causes the value from
6308 rcupdate.rcu_cpu_stall_timeout to be used (after
6309 conversion from seconds to milliseconds).
6310
6311 rcupdate.rcu_cpu_stall_cputime= [KNL]
6312 Provide statistics on the cputime and count of
6313 interrupts and tasks during the sampling period. For
6314 multiple continuous RCU stalls, all sampling periods
6315 begin at half of the first RCU stall timeout.
6316
6317 rcupdate.rcu_exp_stall_task_details= [KNL]
6318 Print stack dumps of any tasks blocking the
6319 current expedited RCU grace period during an
6320 expedited RCU CPU stall warning.
6321
6322 rcupdate.rcu_expedited= [KNL]
6323 Use expedited grace-period primitives, for
6324 example, synchronize_rcu_expedited() instead
6325 of synchronize_rcu(). This reduces latency,
6326 but can increase CPU utilization, degrade
6327 real-time latency, and degrade energy efficiency.
6328 No effect on CONFIG_TINY_RCU kernels.
6329
6330 rcupdate.rcu_normal= [KNL]
6331 Use only normal grace-period primitives,
6332 for example, synchronize_rcu() instead of
6333 synchronize_rcu_expedited(). This improves
6334 real-time latency, CPU utilization, and
6335 energy efficiency, but can expose users to
6336 increased grace-period latency. This parameter
6337 overrides rcupdate.rcu_expedited. No effect on
6338 CONFIG_TINY_RCU kernels.
6339
6340 rcupdate.rcu_normal_after_boot= [KNL]
6341 Once boot has completed (that is, after
6342 rcu_end_inkernel_boot() has been invoked), use
6343 only normal grace-period primitives. No effect
6344 on CONFIG_TINY_RCU kernels.
6345
6346 But note that CONFIG_PREEMPT_RT=y kernels enables
6347 this kernel boot parameter, forcibly setting
6348 it to the value one, that is, converting any
6349 post-boot attempt at an expedited RCU grace
6350 period to instead use normal non-expedited
6351 grace-period processing.
6352
6353 rcupdate.rcu_task_collapse_lim= [KNL]
6354 Set the maximum number of callbacks present
6355 at the beginning of a grace period that allows
6356 the RCU Tasks flavors to collapse back to using
6357 a single callback queue. This switching only
6358 occurs when rcupdate.rcu_task_enqueue_lim is
6359 set to the default value of -1.
6360
6361 rcupdate.rcu_task_contend_lim= [KNL]
6362 Set the minimum number of callback-queuing-time
6363 lock-contention events per jiffy required to
6364 cause the RCU Tasks flavors to switch to per-CPU
6365 callback queuing. This switching only occurs
6366 when rcupdate.rcu_task_enqueue_lim is set to
6367 the default value of -1.
6368
6369 rcupdate.rcu_task_enqueue_lim= [KNL]
6370 Set the number of callback queues to use for the
6371 RCU Tasks family of RCU flavors. The default
6372 of -1 allows this to be automatically (and
6373 dynamically) adjusted. This parameter is intended
6374 for use in testing.
6375
6376 rcupdate.rcu_task_lazy_lim= [KNL]
6377 Number of callbacks on a given CPU that will
6378 cancel laziness on that CPU. Use -1 to disable
6379 cancellation of laziness, but be advised that
6380 doing so increases the danger of OOM due to
6381 callback flooding.
6382
6383 rcupdate.rcu_task_stall_info= [KNL]
6384 Set initial timeout in jiffies for RCU task stall
6385 informational messages, which give some indication
6386 of the problem for those not patient enough to
6387 wait for ten minutes. Informational messages are
6388 only printed prior to the stall-warning message
6389 for a given grace period. Disable with a value
6390 less than or equal to zero. Defaults to ten
6391 seconds. A change in value does not take effect
6392 until the beginning of the next grace period.
6393
6394 rcupdate.rcu_task_stall_info_mult= [KNL]
6395 Multiplier for time interval between successive
6396 RCU task stall informational messages for a given
6397 RCU tasks grace period. This value is clamped
6398 to one through ten, inclusive. It defaults to
6399 the value three, so that the first informational
6400 message is printed 10 seconds into the grace
6401 period, the second at 40 seconds, the third at
6402 160 seconds, and then the stall warning at 600
6403 seconds would prevent a fourth at 640 seconds.
6404
6405 rcupdate.rcu_task_stall_timeout= [KNL]
6406 Set timeout in jiffies for RCU task stall
6407 warning messages. Disable with a value less
6408 than or equal to zero. Defaults to ten minutes.
6409 A change in value does not take effect until
6410 the beginning of the next grace period.
6411
6412 rcupdate.rcu_tasks_lazy_ms= [KNL]
6413 Set timeout in milliseconds RCU Tasks asynchronous
6414 callback batching for call_rcu_tasks().
6415 A negative value will take the default. A value
6416 of zero will disable batching. Batching is
6417 always disabled for synchronize_rcu_tasks().
6418
6419 rcupdate.rcu_self_test= [KNL]
6420 Run the RCU early boot self tests
6421
6422 rdinit= [KNL]
6423 Format: <full_path>
6424 Run specified binary instead of /init from the ramdisk,
6425 used for early userspace startup. See initrd.
6426
6427 rdrand= [X86,EARLY]
6428 force - Override the decision by the kernel to hide the
6429 advertisement of RDRAND support (this affects
6430 certain AMD processors because of buggy BIOS
6431 support, specifically around the suspend/resume
6432 path).
6433
6434 rdt= [HW,X86,RDT]
6435 Turn on/off individual RDT features. List is:
6436 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
6437 mba, smba, bmec, abmc, sdciae, energy[:guid],
6438 perf[:guid].
6439 E.g. to turn on cmt and turn off mba use:
6440 rdt=cmt,!mba
6441 To turn off all energy telemetry monitoring and ensure that
6442 perf telemetry monitoring associated with guid 0x12345
6443 is enabled use:
6444 rdt=!energy,perf:0x12345
6445
6446 reboot= [KNL]
6447 Format (x86 or x86_64):
6448 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
6449 [[,]s[mp]#### \
6450 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
6451 [[,]f[orce]
6452 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
6453 (prefix with 'panic_' to set mode for panic
6454 reboot only),
6455 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
6456 reboot_force is either force or not specified,
6457 reboot_cpu is s[mp]#### with #### being the processor
6458 to be used for rebooting.
6459
6460 acpi
6461 Use the ACPI RESET_REG in the FADT. If ACPI is not
6462 configured or the ACPI reset does not work, the reboot
6463 path attempts the reset using the keyboard controller.
6464
6465 bios
6466 Use the CPU reboot vector for warm reset
6467
6468 cold
6469 Set the cold reboot flag
6470
6471 default
6472 There are some built-in platform specific "quirks"
6473 - you may see: "reboot: <name> series board detected.
6474 Selecting <type> for reboots." In the case where you
6475 think the quirk is in error (e.g. you have newer BIOS,
6476 or newer board) using this option will ignore the
6477 built-in quirk table, and use the generic default
6478 reboot actions.
6479
6480 efi
6481 Use efi reset_system runtime service. If EFI is not
6482 configured or the EFI reset does not work, the reboot
6483 path attempts the reset using the keyboard controller.
6484
6485 force
6486 Don't stop other CPUs on reboot. This can make reboot
6487 more reliable in some cases.
6488
6489 kbd
6490 Use the keyboard controller. cold reset (default)
6491
6492 pci
6493 Use a write to the PCI config space register 0xcf9 to
6494 trigger reboot.
6495
6496 triple
6497 Force a triple fault (init)
6498
6499 warm
6500 Don't set the cold reboot flag
6501
6502 Using warm reset will be much faster especially on big
6503 memory systems because the BIOS will not go through
6504 the memory check. Disadvantage is that not all
6505 hardware will be completely reinitialized on reboot so
6506 there may be boot problems on some systems.
6507
6508
6509 refscale.holdoff= [KNL]
6510 Set test-start holdoff period. The purpose of
6511 this parameter is to delay the start of the
6512 test until boot completes in order to avoid
6513 interference.
6514
6515 refscale.lookup_instances= [KNL]
6516 Number of data elements to use for the forms of
6517 SLAB_TYPESAFE_BY_RCU testing. A negative number
6518 is negated and multiplied by nr_cpu_ids, while
6519 zero specifies nr_cpu_ids.
6520
6521 refscale.loops= [KNL]
6522 Set the number of loops over the synchronization
6523 primitive under test. Increasing this number
6524 reduces noise due to loop start/end overhead,
6525 but the default has already reduced the per-pass
6526 noise to a handful of picoseconds on ca. 2020
6527 x86 laptops.
6528
6529 refscale.nreaders= [KNL]
6530 Set number of readers. The default value of -1
6531 selects N, where N is roughly 75% of the number
6532 of CPUs. A value of zero is an interesting choice.
6533
6534 refscale.nruns= [KNL]
6535 Set number of runs, each of which is dumped onto
6536 the console log.
6537
6538 refscale.readdelay= [KNL]
6539 Set the read-side critical-section duration,
6540 measured in microseconds.
6541
6542 refscale.scale_type= [KNL]
6543 Specify the read-protection implementation to test.
6544
6545 refscale.shutdown= [KNL]
6546 Shut down the system at the end of the performance
6547 test. This defaults to 1 (shut it down) when
6548 refscale is built into the kernel and to 0 (leave
6549 it running) when refscale is built as a module.
6550
6551 refscale.verbose= [KNL]
6552 Enable additional printk() statements.
6553
6554 refscale.verbose_batched= [KNL]
6555 Batch the additional printk() statements. If zero
6556 (the default) or negative, print everything. Otherwise,
6557 print every Nth verbose statement, where N is the value
6558 specified.
6559
6560 regulator_ignore_unused
6561 [REGULATOR]
6562 Prevents regulator framework from disabling regulators
6563 that are unused, due no driver claiming them. This may
6564 be useful for debug and development, but should not be
6565 needed on a platform with proper driver support.
6566
6567 relax_domain_level=
6568 [KNL, SMP] Set scheduler's default relax_domain_level.
6569 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
6570
6571 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
6572 Format: <base1>,<size1>[,<base2>,<size2>,...]
6573 Reserve I/O ports or memory so the kernel won't use
6574 them. If <base> is less than 0x10000, the region
6575 is assumed to be I/O ports; otherwise it is memory.
6576
6577 reserve_mem= [RAM]
6578 Format: nn[KMG]:<align>:<label>
6579 Reserve physical memory and label it with a name that
6580 other subsystems can use to access it. This is typically
6581 used for systems that do not wipe the RAM, and this command
6582 line will try to reserve the same physical memory on
6583 soft reboots. Note, it is not guaranteed to be the same
6584 location. For example, if anything about the system changes
6585 or if booting a different kernel. It can also fail if KASLR
6586 places the kernel at the location of where the RAM reservation
6587 was from a previous boot, the new reservation will be at a
6588 different location.
6589 Any subsystem using this feature must add a way to verify
6590 that the contents of the physical memory is from a previous
6591 boot, as there may be cases where the memory will not be
6592 located at the same location.
6593
6594 The format is size:align:label for example, to request
6595 12 megabytes of 4096 alignment for ramoops:
6596
6597 reserve_mem=12M:4096:oops ramoops.mem_name=oops
6598
6599 reservetop= [X86-32,EARLY]
6600 Format: nn[KMG]
6601 Reserves a hole at the top of the kernel virtual
6602 address space.
6603
6604 reset_devices [KNL] Force drivers to reset the underlying device
6605 during initialization.
6606
6607 resume= [SWSUSP]
6608 Specify the partition device for software suspend
6609 Format:
6610 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
6611
6612 resume_offset= [SWSUSP]
6613 Specify the offset from the beginning of the partition
6614 given by "resume=" at which the swap header is located,
6615 in <PAGE_SIZE> units (needed only for swap files).
6616 See Documentation/power/swsusp-and-swap-files.rst
6617
6618 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
6619 read the resume files
6620
6621 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
6622 Useful for devices that are detected asynchronously
6623 (e.g. USB and MMC devices).
6624
6625 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
6626 be accessible via /sys/firmware/initrd.
6627
6628 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
6629 Speculative Code Execution with Return Instructions)
6630 vulnerability.
6631
6632 AMD-based UNRET and IBPB mitigations alone do not stop
6633 sibling threads from influencing the predictions of other
6634 sibling threads. For that reason, STIBP is used on pro-
6635 cessors that support it, and mitigate SMT on processors
6636 that don't.
6637
6638 off - no mitigation
6639 auto - automatically select a mitigation
6640 auto,nosmt - automatically select a mitigation,
6641 disabling SMT if necessary for
6642 the full mitigation (only on Zen1
6643 and older without STIBP).
6644 ibpb - On AMD, mitigate short speculation
6645 windows on basic block boundaries too.
6646 Safe, highest perf impact. It also
6647 enables STIBP if present. Not suitable
6648 on Intel.
6649 ibpb,nosmt - Like "ibpb" above but will disable SMT
6650 when STIBP is not available. This is
6651 the alternative for systems which do not
6652 have STIBP.
6653 unret - Force enable untrained return thunks,
6654 only effective on AMD f15h-f17h based
6655 systems.
6656 unret,nosmt - Like unret, but will disable SMT when STIBP
6657 is not available. This is the alternative for
6658 systems which do not have STIBP.
6659
6660 Selecting 'auto' will choose a mitigation method at run
6661 time according to the CPU.
6662
6663 Not specifying this option is equivalent to retbleed=auto.
6664
6665 rfkill.default_state=
6666 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
6667 etc. communication is blocked by default.
6668 1 Unblocked.
6669
6670 rfkill.master_switch_mode=
6671 0 The "airplane mode" button does nothing.
6672 1 The "airplane mode" button toggles between everything
6673 blocked and the previous configuration.
6674 2 The "airplane mode" button toggles between everything
6675 blocked and everything unblocked.
6676
6677 ring3mwait=disable
6678 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
6679 CPUs.
6680
6681 riscv_isa_fallback [RISCV,EARLY]
6682 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit
6683 falling back to detecting extension support by parsing
6684 "riscv,isa" property on devicetree systems when the
6685 replacement properties are not found. See the Kconfig
6686 entry for RISCV_ISA_FALLBACK.
6687
6688 riscv_nousercfi=
6689 all Disable user CFI ABI to userspace even if cpu extension
6690 are available.
6691 bcfi Disable user backward CFI ABI to userspace even if
6692 the shadow stack extension is available.
6693 fcfi Disable user forward CFI ABI to userspace even if the
6694 landing pad extension is available.
6695
6696 ro [KNL] Mount root device read-only on boot
6697
6698 rodata= [KNL,EARLY]
6699 on Mark read-only kernel memory as read-only (default).
6700 off Leave read-only kernel memory writable for debugging.
6701 noalias Mark read-only kernel memory as read-only but retain
6702 writable aliases in the direct map for regions outside
6703 of the kernel image. [arm64]
6704
6705 rockchip.usb_uart
6706 [EARLY]
6707 Enable the uart passthrough on the designated usb port
6708 on Rockchip SoCs. When active, the signals of the
6709 debug-uart get routed to the D+ and D- pins of the usb
6710 port and the regular usb controller gets disabled.
6711
6712 root= [KNL] Root filesystem
6713 Usually this is a block device specifier of some kind,
6714 see the early_lookup_bdev comment in
6715 block/early-lookup.c for details.
6716 Alternatively this can be "ram" for the legacy initial
6717 ramdisk, "nfs" and "cifs" for root on a network file
6718 system, or "mtd" and "ubi" for mounting from raw flash.
6719
6720 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
6721 mount the root filesystem
6722
6723 rootflags= [KNL] Set root filesystem mount option string
6724
6725 rseq_slice_ext= [KNL] RSEQ based time slice extension
6726 Format: boolean
6727 Control enablement of RSEQ based time slice extension.
6728 Default is 'on'.
6729
6730 initramfs_options= [KNL]
6731 Specify mount options for the initramfs mount.
6732
6733 rootfstype= [KNL] Set root filesystem type
6734
6735 rootwait [KNL] Wait (indefinitely) for root device to show up.
6736 Useful for devices that are detected asynchronously
6737 (e.g. USB and MMC devices).
6738
6739 rootwait= [KNL] Maximum time (in seconds) to wait for root device
6740 to show up before attempting to mount the root
6741 filesystem.
6742
6743 rproc_mem=nn[KMG][@address]
6744 [KNL,ARM,CMA] Remoteproc physical memory block.
6745 Memory area to be used by remote processor image,
6746 managed by CMA.
6747
6748 rseq_debug= [KNL] Enable or disable restartable sequence
6749 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE.
6750 Format: <bool>
6751
6752 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling
6753 when CONFIG_RT_GROUP_SCHED=y. Defaults to
6754 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED.
6755 Format: <bool>
6756
6757 rw [KNL] Mount root device read-write on boot
6758
6759 S [KNL] Run init in single mode
6760
6761 s390_iommu= [HW,S390]
6762 Set s390 IOTLB flushing mode
6763 strict
6764 With strict flushing every unmap operation will result
6765 in an IOTLB flush. Default is lazy flushing before
6766 reuse, which is faster. Deprecated, equivalent to
6767 iommu.strict=1.
6768
6769 s390_iommu_aperture= [KNL,S390]
6770 Specifies the size of the per device DMA address space
6771 accessible through the DMA and IOMMU APIs as a decimal
6772 factor of the size of main memory.
6773 The default is 1 meaning that one can concurrently use
6774 as many DMA addresses as physical memory is installed,
6775 if supported by hardware, and thus map all of memory
6776 once. With a value of 2 one can map all of memory twice
6777 and so on. As a special case a factor of 0 imposes no
6778 restrictions other than those given by hardware at the
6779 cost of significant additional memory use for tables.
6780
6781 sa1100ir [NET]
6782 See drivers/net/irda/sa1100_ir.c.
6783
6784 sched_proxy_exec= [KNL]
6785 Enables or disables "proxy execution" style
6786 solution to mutex-based priority inversion.
6787 Format: <bool>
6788
6789 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.
6790
6791 schedstats= [KNL,X86] Enable or disable scheduled statistics.
6792 Allowed values are enable and disable. This feature
6793 incurs a small amount of overhead in the scheduler
6794 but is useful for debugging and performance tuning.
6795
6796 sched_thermal_decay_shift=
6797 [Deprecated]
6798 [KNL, SMP] Set a decay shift for scheduler thermal
6799 pressure signal. Thermal pressure signal follows the
6800 default decay period of other scheduler pelt
6801 signals(usually 32 ms but configurable). Setting
6802 sched_thermal_decay_shift will left shift the decay
6803 period for the thermal pressure signal by the shift
6804 value.
6805 i.e. with the default pelt decay period of 32 ms
6806 sched_thermal_decay_shift thermal pressure decay pr
6807 1 64 ms
6808 2 128 ms
6809 and so on.
6810 Format: integer between 0 and 10
6811 Default is 0.
6812
6813 scftorture.holdoff= [KNL]
6814 Number of seconds to hold off before starting
6815 test. Defaults to zero for module insertion and
6816 to 10 seconds for built-in smp_call_function()
6817 tests.
6818
6819 scftorture.longwait= [KNL]
6820 Request ridiculously long waits randomly selected
6821 up to the chosen limit in seconds. Zero (the
6822 default) disables this feature. Please note
6823 that requesting even small non-zero numbers of
6824 seconds can result in RCU CPU stall warnings,
6825 softlockup complaints, and so on.
6826
6827 scftorture.nthreads= [KNL]
6828 Number of kthreads to spawn to invoke the
6829 smp_call_function() family of functions.
6830 The default of -1 specifies a number of kthreads
6831 equal to the number of CPUs.
6832
6833 scftorture.onoff_holdoff= [KNL]
6834 Number seconds to wait after the start of the
6835 test before initiating CPU-hotplug operations.
6836
6837 scftorture.onoff_interval= [KNL]
6838 Number seconds to wait between successive
6839 CPU-hotplug operations. Specifying zero (which
6840 is the default) disables CPU-hotplug operations.
6841
6842 scftorture.shutdown_secs= [KNL]
6843 The number of seconds following the start of the
6844 test after which to shut down the system. The
6845 default of zero avoids shutting down the system.
6846 Non-zero values are useful for automated tests.
6847
6848 scftorture.stat_interval= [KNL]
6849 The number of seconds between outputting the
6850 current test statistics to the console. A value
6851 of zero disables statistics output.
6852
6853 scftorture.stutter_cpus= [KNL]
6854 The number of jiffies to wait between each change
6855 to the set of CPUs under test.
6856
6857 scftorture.use_cpus_read_lock= [KNL]
6858 Use use_cpus_read_lock() instead of the default
6859 preempt_disable() to disable CPU hotplug
6860 while invoking one of the smp_call_function*()
6861 functions.
6862
6863 scftorture.verbose= [KNL]
6864 Enable additional printk() statements.
6865
6866 scftorture.weight_single= [KNL]
6867 The probability weighting to use for the
6868 smp_call_function_single() function with a zero
6869 "wait" parameter. A value of -1 selects the
6870 default if all other weights are -1. However,
6871 if at least one weight has some other value, a
6872 value of -1 will instead select a weight of zero.
6873
6874 scftorture.weight_single_wait= [KNL]
6875 The probability weighting to use for the
6876 smp_call_function_single() function with a
6877 non-zero "wait" parameter. See weight_single.
6878
6879 scftorture.weight_many= [KNL]
6880 The probability weighting to use for the
6881 smp_call_function_many() function with a zero
6882 "wait" parameter. See weight_single.
6883 Note well that setting a high probability for
6884 this weighting can place serious IPI load
6885 on the system.
6886
6887 scftorture.weight_many_wait= [KNL]
6888 The probability weighting to use for the
6889 smp_call_function_many() function with a
6890 non-zero "wait" parameter. See weight_single
6891 and weight_many.
6892
6893 scftorture.weight_all= [KNL]
6894 The probability weighting to use for the
6895 smp_call_function_all() function with a zero
6896 "wait" parameter. See weight_single and
6897 weight_many.
6898
6899 scftorture.weight_all_wait= [KNL]
6900 The probability weighting to use for the
6901 smp_call_function_all() function with a
6902 non-zero "wait" parameter. See weight_single
6903 and weight_many.
6904
6905 sdw_mclk_divider=[SDW]
6906 Specify the MCLK divider for Intel SoundWire buses in
6907 case the BIOS does not provide the clock rate properly.
6908
6909 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate
6910 xtime_lock contention on larger systems, and/or RCU lock
6911 contention on all systems with CONFIG_MAXSMP set.
6912 Format: { "0" | "1" }
6913 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
6914 1 -- enable.
6915 Note: increases power consumption, thus should only be
6916 enabled if running jitter sensitive (HPC/RT) workloads.
6917
6918 security= [SECURITY] Choose a legacy "major" security module to
6919 enable at boot. This has been deprecated by the
6920 "lsm=" parameter.
6921
6922 selinux= [SELINUX] Disable or enable SELinux at boot time.
6923 Format: { "0" | "1" }
6924 See security/selinux/Kconfig help text.
6925 0 -- disable.
6926 1 -- enable.
6927 Default value is 1.
6928
6929 serialnumber [BUGS=X86-32]
6930
6931 sev=option[,option...] [X86-64]
6932
6933 debug
6934 Enable debug messages.
6935
6936 nosnp
6937 Do not enable SEV-SNP (applies to host/hypervisor
6938 only). Setting 'nosnp' avoids the RMP check overhead
6939 in memory accesses when users do not want to run
6940 SEV-SNP guests.
6941
6942 shapers= [NET]
6943 Maximal number of shapers.
6944
6945 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
6946 Limit apic dumping. The parameter defines the maximal
6947 number of local apics being dumped. Also it is possible
6948 to set it to "all" by meaning -- no limit here.
6949 Format: { 1 (default) | 2 | ... | all }.
6950 The parameter valid if only apic=debug or
6951 apic=verbose is specified.
6952 Example: apic=debug show_lapic=all
6953
6954 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM]
6955 Enabling slab_debug allows one to determine the
6956 culprit if slab objects become corrupted. Enabling
6957 slab_debug can create guard zones around objects and
6958 may poison objects when not in use. Also tracks the
6959 last alloc / free. For more information see
6960 Documentation/admin-guide/mm/slab.rst.
6961 (slub_debug legacy name also accepted for now)
6962
6963 Using this option implies the "no_hash_pointers"
6964 option which can be undone by adding the
6965 "hash_pointers=always" option.
6966
6967 slab_max_order= [MM]
6968 Determines the maximum allowed order for slabs.
6969 A high setting may cause OOMs due to memory
6970 fragmentation. For more information see
6971 Documentation/admin-guide/mm/slab.rst.
6972 (slub_max_order legacy name also accepted for now)
6973
6974 slab_merge [MM]
6975 Enable merging of slabs with similar size when the
6976 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
6977 (slub_merge legacy name also accepted for now)
6978
6979 slab_min_objects= [MM]
6980 The minimum number of objects per slab. SLUB will
6981 increase the slab order up to slab_max_order to
6982 generate a sufficiently large slab able to contain
6983 the number of objects indicated. The higher the number
6984 of objects the smaller the overhead of tracking slabs
6985 and the less frequently locks need to be acquired.
6986 For more information see
6987 Documentation/admin-guide/mm/slab.rst.
6988 (slub_min_objects legacy name also accepted for now)
6989
6990 slab_min_order= [MM]
6991 Determines the minimum page order for slabs. Must be
6992 lower or equal to slab_max_order. For more information see
6993 Documentation/admin-guide/mm/slab.rst.
6994 (slub_min_order legacy name also accepted for now)
6995
6996 slab_nomerge [MM]
6997 Disable merging of slabs with similar size. May be
6998 necessary if there is some reason to distinguish
6999 allocs to different slabs, especially in hardened
7000 environments where the risk of heap overflows and
7001 layout control by attackers can usually be
7002 frustrated by disabling merging. This will reduce
7003 most of the exposure of a heap attack to a single
7004 cache (risks via metadata attacks are mostly
7005 unchanged). Debug options disable merging on their
7006 own.
7007 For more information see
7008 Documentation/admin-guide/mm/slab.rst.
7009 (slub_nomerge legacy name also accepted for now)
7010
7011 slab_strict_numa [MM]
7012 Support memory policies on a per object level
7013 in the slab allocator. The default is for memory
7014 policies to be applied at the folio level when
7015 a new folio is needed or a partial folio is
7016 retrieved from the lists. Increases overhead
7017 in the slab fastpaths but gains more accurate
7018 NUMA kernel object placement which helps with slow
7019 interconnects in NUMA systems.
7020
7021 slram= [HW,MTD]
7022
7023 smart2= [HW]
7024 Format: <io1>[,<io2>[,...,<io8>]]
7025
7026 smp.csd_lock_timeout= [KNL]
7027 Specify the period of time in milliseconds
7028 that smp_call_function() and friends will wait
7029 for a CPU to release the CSD lock. This is
7030 useful when diagnosing bugs involving CPUs
7031 disabling interrupts for extended periods
7032 of time. Defaults to 5,000 milliseconds, and
7033 setting a value of zero disables this feature.
7034 This feature may be more efficiently disabled
7035 using the csdlock_debug- kernel parameter.
7036
7037 smp.panic_on_ipistall= [KNL]
7038 If a csd_lock_timeout extends for more than
7039 the specified number of milliseconds, panic the
7040 system. By default, let CSD-lock acquisition
7041 take as long as they take. Specifying 300,000
7042 for this value provides a 5-minute timeout.
7043
7044 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
7045 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
7046 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
7047 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
7048 smsc-ircc2.ircc_irq= [HW] IRQ line
7049 smsc-ircc2.ircc_dma= [HW] DMA channel
7050 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
7051 0: Toshiba Satellite 1800 (GP data pin select)
7052 1: Fast pin select (default)
7053 2: ATC IRMode
7054
7055 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads
7056 (logical CPUs) to use per physical CPU on systems
7057 capable of symmetric multithreading (SMT). Will
7058 be capped to the actual hardware limit.
7059 Format: <integer>
7060 Default: -1 (no limit)
7061
7062 softlockup_panic=
7063 [KNL] Should the soft-lockup detector generate panics.
7064 Format: <int>
7065
7066 A value of non-zero instructs the soft-lockup detector
7067 to panic the machine when a soft-lockup duration exceeds
7068 N thresholds. It is also controlled by the kernel.softlockup_panic
7069 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
7070 respective build-time switch to that functionality.
7071
7072 softlockup_all_cpu_backtrace=
7073 [KNL] Should the soft-lockup detector generate
7074 backtraces on all cpus.
7075 Format: 0 | 1
7076
7077 sonypi.*= [HW] Sony Programmable I/O Control Device driver
7078 See Documentation/admin-guide/laptops/sonypi.rst
7079
7080 spectre_bhi= [X86] Control mitigation of Branch History Injection
7081 (BHI) vulnerability. This setting affects the
7082 deployment of the HW BHI control and the SW BHB
7083 clearing sequence.
7084
7085 on - (default) Enable the HW or SW mitigation as
7086 needed. This protects the kernel from
7087 both syscalls and VMs.
7088 vmexit - On systems which don't have the HW mitigation
7089 available, enable the SW mitigation on vmexit
7090 ONLY. On such systems, the host kernel is
7091 protected from VM-originated BHI attacks, but
7092 may still be vulnerable to syscall attacks.
7093 off - Disable the mitigation.
7094
7095 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2
7096 (indirect branch speculation) vulnerability.
7097 The default operation protects the kernel from
7098 user space attacks.
7099
7100 on - unconditionally enable, implies
7101 spectre_v2_user=on
7102 off - unconditionally disable, implies
7103 spectre_v2_user=off
7104 auto - kernel detects whether your CPU model is
7105 vulnerable
7106
7107 Selecting 'on' will, and 'auto' may, choose a
7108 mitigation method at run time according to the
7109 CPU, the available microcode, the setting of the
7110 CONFIG_MITIGATION_RETPOLINE configuration option,
7111 and the compiler with which the kernel was built.
7112
7113 Selecting 'on' will also enable the mitigation
7114 against user space to user space task attacks.
7115 Selecting specific mitigation does not force enable
7116 user mitigations.
7117
7118 Selecting 'off' will disable both the kernel and
7119 the user space protections.
7120
7121 Specific mitigations can also be selected manually:
7122
7123 retpoline - replace indirect branches
7124 retpoline,generic - Retpolines
7125 retpoline,lfence - LFENCE; indirect branch
7126 retpoline,amd - alias for retpoline,lfence
7127 eibrs - Enhanced/Auto IBRS
7128 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines
7129 eibrs,lfence - Enhanced/Auto IBRS + LFENCE
7130 ibrs - use IBRS to protect kernel
7131
7132 Not specifying this option is equivalent to
7133 spectre_v2=auto.
7134
7135 spectre_v2_user=
7136 [X86] Control mitigation of Spectre variant 2
7137 (indirect branch speculation) vulnerability between
7138 user space tasks
7139
7140 on - Unconditionally enable mitigations. Is
7141 enforced by spectre_v2=on
7142
7143 off - Unconditionally disable mitigations. Is
7144 enforced by spectre_v2=off
7145
7146 prctl - Indirect branch speculation is enabled,
7147 but mitigation can be enabled via prctl
7148 per thread. The mitigation control state
7149 is inherited on fork.
7150
7151 prctl,ibpb
7152 - Like "prctl" above, but only STIBP is
7153 controlled per thread. IBPB is issued
7154 always when switching between different user
7155 space processes.
7156
7157 seccomp
7158 - Same as "prctl" above, but all seccomp
7159 threads will enable the mitigation unless
7160 they explicitly opt out.
7161
7162 seccomp,ibpb
7163 - Like "seccomp" above, but only STIBP is
7164 controlled per thread. IBPB is issued
7165 always when switching between different
7166 user space processes.
7167
7168 auto - Kernel selects the mitigation depending on
7169 the available CPU features and vulnerability.
7170
7171 Default mitigation: "prctl"
7172
7173 Not specifying this option is equivalent to
7174 spectre_v2_user=auto.
7175
7176 spec_rstack_overflow=
7177 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs
7178
7179 off - Disable mitigation
7180 microcode - Enable microcode mitigation only
7181 safe-ret - Enable sw-only safe RET mitigation (default)
7182 ibpb - Enable mitigation by issuing IBPB on
7183 kernel entry
7184 ibpb-vmexit - Issue IBPB only on VMEXIT
7185 (cloud-specific mitigation)
7186
7187 spec_store_bypass_disable=
7188 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation
7189 (Speculative Store Bypass vulnerability)
7190
7191 Certain CPUs are vulnerable to an exploit against a
7192 a common industry wide performance optimization known
7193 as "Speculative Store Bypass" in which recent stores
7194 to the same memory location may not be observed by
7195 later loads during speculative execution. The idea
7196 is that such stores are unlikely and that they can
7197 be detected prior to instruction retirement at the
7198 end of a particular speculation execution window.
7199
7200 In vulnerable processors, the speculatively forwarded
7201 store can be used in a cache side channel attack, for
7202 example to read memory to which the attacker does not
7203 directly have access (e.g. inside sandboxed code).
7204
7205 This parameter controls whether the Speculative Store
7206 Bypass optimization is used.
7207
7208 On x86 the options are:
7209
7210 on - Unconditionally disable Speculative Store Bypass
7211 off - Unconditionally enable Speculative Store Bypass
7212 auto - Kernel detects whether the CPU model contains an
7213 implementation of Speculative Store Bypass and
7214 picks the most appropriate mitigation. If the
7215 CPU is not vulnerable, "off" is selected. If the
7216 CPU is vulnerable the default mitigation is
7217 architecture and Kconfig dependent. See below.
7218 prctl - Control Speculative Store Bypass per thread
7219 via prctl. Speculative Store Bypass is enabled
7220 for a process by default. The state of the control
7221 is inherited on fork.
7222 seccomp - Same as "prctl" above, but all seccomp threads
7223 will disable SSB unless they explicitly opt out.
7224
7225 Default mitigations:
7226 X86: "prctl"
7227
7228 On powerpc the options are:
7229
7230 on,auto - On Power8 and Power9 insert a store-forwarding
7231 barrier on kernel entry and exit. On Power7
7232 perform a software flush on kernel entry and
7233 exit.
7234 off - No action.
7235
7236 Not specifying this option is equivalent to
7237 spec_store_bypass_disable=auto.
7238
7239 split_lock_detect=
7240 [X86] Enable split lock detection or bus lock detection
7241
7242 When enabled (and if hardware support is present), atomic
7243 instructions that access data across cache line
7244 boundaries will result in an alignment check exception
7245 for split lock detection or a debug exception for
7246 bus lock detection.
7247
7248 off - not enabled
7249
7250 warn - the kernel will emit rate-limited warnings
7251 about applications triggering the #AC
7252 exception or the #DB exception. This mode is
7253 the default on CPUs that support split lock
7254 detection or bus lock detection. Default
7255 behavior is by #AC if both features are
7256 enabled in hardware.
7257
7258 fatal - the kernel will send SIGBUS to applications
7259 that trigger the #AC exception or the #DB
7260 exception. Default behavior is by #AC if
7261 both features are enabled in hardware.
7262
7263 ratelimit:N -
7264 Set system wide rate limit to N bus locks
7265 per second for bus lock detection.
7266 0 < N <= 1000.
7267
7268 N/A for split lock detection.
7269
7270
7271 If an #AC exception is hit in the kernel or in
7272 firmware (i.e. not while executing in user mode)
7273 the kernel will oops in either "warn" or "fatal"
7274 mode.
7275
7276 #DB exception for bus lock is triggered only when
7277 CPL > 0.
7278
7279 srbds= [X86,INTEL,EARLY]
7280 Control the Special Register Buffer Data Sampling
7281 (SRBDS) mitigation.
7282
7283 Certain CPUs are vulnerable to an MDS-like
7284 exploit which can leak bits from the random
7285 number generator.
7286
7287 By default, this issue is mitigated by
7288 microcode. However, the microcode fix can cause
7289 the RDRAND and RDSEED instructions to become
7290 much slower. Among other effects, this will
7291 result in reduced throughput from /dev/urandom.
7292
7293 The microcode mitigation can be disabled with
7294 the following option:
7295
7296 off: Disable mitigation and remove
7297 performance impact to RDRAND and RDSEED
7298
7299 srcutree.big_cpu_lim [KNL]
7300 Specifies the number of CPUs constituting a
7301 large system, such that srcu_struct structures
7302 should immediately allocate an srcu_node array.
7303 This kernel-boot parameter defaults to 128,
7304 but takes effect only when the low-order four
7305 bits of srcutree.convert_to_big is equal to 3
7306 (decide at boot).
7307
7308 srcutree.convert_to_big [KNL]
7309 Specifies under what conditions an SRCU tree
7310 srcu_struct structure will be converted to big
7311 form, that is, with an rcu_node tree:
7312
7313 0: Never.
7314 1: At init_srcu_struct() time.
7315 2: When rcutorture decides to.
7316 3: Decide at boot time (default).
7317 0x1X: Above plus if high contention.
7318
7319 Either way, the srcu_node tree will be sized based
7320 on the actual runtime number of CPUs (nr_cpu_ids)
7321 instead of the compile-time CONFIG_NR_CPUS.
7322
7323 srcutree.counter_wrap_check [KNL]
7324 Specifies how frequently to check for
7325 grace-period sequence counter wrap for the
7326 srcu_data structure's ->srcu_gp_seq_needed field.
7327 The greater the number of bits set in this kernel
7328 parameter, the less frequently counter wrap will
7329 be checked for. Note that the bottom two bits
7330 are ignored.
7331
7332 srcutree.exp_holdoff [KNL]
7333 Specifies how many nanoseconds must elapse
7334 since the end of the last SRCU grace period for
7335 a given srcu_struct until the next normal SRCU
7336 grace period will be considered for automatic
7337 expediting. Set to zero to disable automatic
7338 expediting.
7339
7340 srcutree.srcu_max_nodelay [KNL]
7341 Specifies the number of no-delay instances
7342 per jiffy for which the SRCU grace period
7343 worker thread will be rescheduled with zero
7344 delay. Beyond this limit, worker thread will
7345 be rescheduled with a sleep delay of one jiffy.
7346
7347 srcutree.srcu_max_nodelay_phase [KNL]
7348 Specifies the per-grace-period phase, number of
7349 non-sleeping polls of readers. Beyond this limit,
7350 grace period worker thread will be rescheduled
7351 with a sleep delay of one jiffy, between each
7352 rescan of the readers, for a grace period phase.
7353
7354 srcutree.srcu_retry_check_delay [KNL]
7355 Specifies number of microseconds of non-sleeping
7356 delay between each non-sleeping poll of readers.
7357
7358 srcutree.small_contention_lim [KNL]
7359 Specifies the number of update-side contention
7360 events per jiffy will be tolerated before
7361 initiating a conversion of an srcu_struct
7362 structure to big form. Note that the value of
7363 srcutree.convert_to_big must have the 0x10 bit
7364 set for contention-based conversions to occur.
7365
7366 ssbd= [ARM64,HW,EARLY]
7367 Speculative Store Bypass Disable control
7368
7369 On CPUs that are vulnerable to the Speculative
7370 Store Bypass vulnerability and offer a
7371 firmware based mitigation, this parameter
7372 indicates how the mitigation should be used:
7373
7374 force-on: Unconditionally enable mitigation for
7375 for both kernel and userspace
7376 force-off: Unconditionally disable mitigation for
7377 for both kernel and userspace
7378 kernel: Always enable mitigation in the
7379 kernel, and offer a prctl interface
7380 to allow userspace to register its
7381 interest in being mitigated too.
7382
7383 stack_guard_gap= [MM]
7384 override the default stack gap protection. The value
7385 is in page units and it defines how many pages prior
7386 to (for stacks growing down) resp. after (for stacks
7387 growing up) the main stack are reserved for no other
7388 mapping. Default value is 256 pages.
7389
7390 stack_depot_disable= [KNL,EARLY]
7391 Setting this to true through kernel command line will
7392 disable the stack depot thereby saving the static memory
7393 consumed by the stack hash table. By default this is set
7394 to false.
7395
7396 stack_depot_max_pools= [KNL,EARLY]
7397 Specify the maximum number of pools to use for storing
7398 stack traces. Pools are allocated on-demand up to this
7399 limit. Default value is 8191 pools.
7400
7401 stacktrace [FTRACE]
7402 Enable the stack tracer on boot up.
7403
7404 stacktrace_filter=[function-list]
7405 [FTRACE] Limit the functions that the stack tracer
7406 will trace at boot up. function-list is a comma-separated
7407 list of functions. This list can be changed at run
7408 time by the stack_trace_filter file in the debugfs
7409 tracing directory. Note, this enables stack tracing
7410 and the stacktrace above is not needed.
7411
7412 sti= [PARISC,HW]
7413 Format: <num>
7414 Set the STI (builtin display/keyboard on the HP-PARISC
7415 machines) console (graphic card) which should be used
7416 as the initial boot-console.
7417 See also comment in drivers/video/console/sticore.c.
7418
7419 sti_font= [HW]
7420 See comment in drivers/video/console/sticore.c.
7421
7422 stifb= [HW]
7423 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
7424
7425 strict_sas_size=
7426 [X86]
7427 Format: <bool>
7428 Enable or disable strict sigaltstack size checks
7429 against the required signal frame size which
7430 depends on the supported FPU features. This can
7431 be used to filter out binaries which have
7432 not yet been made aware of AT_MINSIGSTKSZ.
7433
7434 stress_hpt [PPC,EARLY]
7435 Limits the number of kernel HPT entries in the hash
7436 page table to increase the rate of hash page table
7437 faults on kernel addresses.
7438
7439 stress_slb [PPC,EARLY]
7440 Limits the number of kernel SLB entries, and flushes
7441 them frequently to increase the rate of SLB faults
7442 on kernel addresses.
7443
7444 no_slb_preload [PPC,EARLY]
7445 Disables slb preloading for userspace.
7446
7447 sunrpc.min_resvport=
7448 sunrpc.max_resvport=
7449 [NFS,SUNRPC]
7450 SunRPC servers often require that client requests
7451 originate from a privileged port (i.e. a port in the
7452 range 0 < portnr < 1024).
7453 An administrator who wishes to reserve some of these
7454 ports for other uses may adjust the range that the
7455 kernel's sunrpc client considers to be privileged
7456 using these two parameters to set the minimum and
7457 maximum port values.
7458
7459 sunrpc.svc_rpc_per_connection_limit=
7460 [NFS,SUNRPC]
7461 Limit the number of requests that the server will
7462 process in parallel from a single connection.
7463 The default value is 0 (no limit).
7464
7465 sunrpc.pool_mode=
7466 [NFS]
7467 Control how the NFS server code allocates CPUs to
7468 service thread pools. Depending on how many NICs
7469 you have and where their interrupts are bound, this
7470 option will affect which CPUs will do NFS serving.
7471 Note: this parameter cannot be changed while the
7472 NFS server is running.
7473
7474 auto the server chooses an appropriate mode
7475 automatically using heuristics
7476 global a single global pool contains all CPUs
7477 percpu one pool for each CPU
7478 pernode one pool for each NUMA node (equivalent
7479 to global on non-NUMA machines)
7480
7481 sunrpc.tcp_slot_table_entries=
7482 sunrpc.udp_slot_table_entries=
7483 [NFS,SUNRPC]
7484 Sets the upper limit on the number of simultaneous
7485 RPC calls that can be sent from the client to a
7486 server. Increasing these values may allow you to
7487 improve throughput, but will also increase the
7488 amount of memory reserved for use by the client.
7489
7490 suspend.pm_test_delay=
7491 [SUSPEND]
7492 Sets the number of seconds to remain in a suspend test
7493 mode before resuming the system (see
7494 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
7495 is set. Default value is 5.
7496
7497 svm= [PPC]
7498 Format: { on | off | y | n | 1 | 0 }
7499 This parameter controls use of the Protected
7500 Execution Facility on pSeries.
7501
7502 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY]
7503 Format: { <int> [,<int>] | force | noforce }
7504 <int> -- Number of I/O TLB slabs
7505 <int> -- Second integer after comma. Number of swiotlb
7506 areas with their own lock. Will be rounded up
7507 to a power of 2.
7508 force -- force using of bounce buffers even if they
7509 wouldn't be automatically used by the kernel
7510 noforce -- Never use bounce buffers (for debugging)
7511
7512 switches= [HW,M68k,EARLY]
7513
7514 sysctl.*= [KNL]
7515 Set a sysctl parameter, right before loading the init
7516 process, as if the value was written to the respective
7517 /proc/sys/... file. Both '.' and '/' are recognized as
7518 separators. Unrecognized parameters and invalid values
7519 are reported in the kernel log. Sysctls registered
7520 later by a loaded module cannot be set this way.
7521 Example: sysctl.vm.swappiness=40
7522
7523 sysrq_always_enabled
7524 [KNL]
7525 Ignore sysrq setting - this boot parameter will
7526 neutralize any effect of /proc/sys/kernel/sysrq.
7527 Useful for debugging.
7528
7529 tcpmhash_entries= [KNL,NET]
7530 Set the number of tcp_metrics_hash slots.
7531 Default value is 8192 or 16384 depending on total
7532 ram pages. This is used to specify the TCP metrics
7533 cache size. See Documentation/networking/ip-sysctl.rst
7534 "tcp_no_metrics_save" section for more details.
7535
7536 tdfx= [HW,DRM]
7537
7538 test_suspend= [SUSPEND]
7539 Format: { "mem" | "standby" | "freeze" }[,N]
7540 Specify "mem" (for Suspend-to-RAM) or "standby" (for
7541 standby suspend) or "freeze" (for suspend type freeze)
7542 as the system sleep state during system startup with
7543 the optional capability to repeat N number of times.
7544 The system is woken from this state using a
7545 wakeup-capable RTC alarm.
7546
7547 thash_entries= [KNL,NET]
7548 Set number of hash buckets for TCP connection
7549
7550 thermal.act= [HW,ACPI]
7551 -1: disable all active trip points in all thermal zones
7552 <degrees C>: override all lowest active trip points
7553
7554 thermal.crt= [HW,ACPI]
7555 -1: disable all critical trip points in all thermal zones
7556 <degrees C>: override all critical trip points
7557
7558 thermal.off= [HW,ACPI]
7559 1: disable ACPI thermal control
7560
7561 thermal.psv= [HW,ACPI]
7562 -1: disable all passive trip points
7563 <degrees C>: override all passive trip points to this
7564 value
7565
7566 thermal.tzp= [HW,ACPI]
7567 Specify global default ACPI thermal zone polling rate
7568 <deci-seconds>: poll all this frequency
7569 0: no polling (default)
7570
7571 thp_anon= [KNL]
7572 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state>
7573 state is one of "always", "madvise", "never" or "inherit".
7574 Control the default behavior of the system with respect
7575 to anonymous transparent hugepages.
7576 Can be used multiple times for multiple anon THP sizes.
7577 See Documentation/admin-guide/mm/transhuge.rst for more
7578 details.
7579
7580 threadirqs [KNL,EARLY]
7581 Force threading of all interrupt handlers except those
7582 marked explicitly IRQF_NO_THREAD.
7583
7584 thp_shmem= [KNL]
7585 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy>
7586 Control the default policy of each hugepage size for the
7587 internal shmem mount. <policy> is one of policies available
7588 for the shmem mount ("always", "inherit", "never", "within_size",
7589 and "advise").
7590 It can be used multiple times for multiple shmem THP sizes.
7591 See Documentation/admin-guide/mm/transhuge.rst for more
7592 details.
7593
7594 topology= [S390,EARLY]
7595 Format: {off | on}
7596 Specify if the kernel should make use of the cpu
7597 topology information if the hardware supports this.
7598 The scheduler will make use of this information and
7599 e.g. base its process migration decisions on it.
7600 Default is on.
7601
7602 torture.disable_onoff_at_boot= [KNL]
7603 Prevent the CPU-hotplug component of torturing
7604 until after init has spawned.
7605
7606 torture.ftrace_dump_at_shutdown= [KNL]
7607 Dump the ftrace buffer at torture-test shutdown,
7608 even if there were no errors. This can be a
7609 very costly operation when many torture tests
7610 are running concurrently, especially on systems
7611 with rotating-rust storage.
7612
7613 torture.verbose_sleep_frequency= [KNL]
7614 Specifies how many verbose printk()s should be
7615 emitted between each sleep. The default of zero
7616 disables verbose-printk() sleeping.
7617
7618 torture.verbose_sleep_duration= [KNL]
7619 Duration of each verbose-printk() sleep in jiffies.
7620
7621 tpm.disable_pcr_integrity= [HW,TPM]
7622 Do not protect PCR registers from unintended physical
7623 access, or interposers in the bus by the means of
7624 having an integrity protected session wrapped around
7625 TPM2_PCR_Extend command. Consider this in a situation
7626 where TPM is heavily utilized by IMA, thus protection
7627 causing a major performance hit, and the space where
7628 machines are deployed is by other means guarded.
7629
7630 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM]
7631 Maximum time in milliseconds to retry sending a message
7632 to the TPM service before giving up. This parameter controls
7633 how long the system will continue retrying when the TPM
7634 service is busy.
7635 Format: <unsigned int>
7636 Default: 2000 (2 seconds)
7637
7638 tpm_suspend_pcr=[HW,TPM]
7639 Format: integer pcr id
7640 Specify that at suspend time, the tpm driver
7641 should extend the specified pcr with zeros,
7642 as a workaround for some chips which fail to
7643 flush the last written pcr on TPM_SaveState.
7644 This will guarantee that all the other pcrs
7645 are saved.
7646
7647 tpm_tis.interrupts= [HW,TPM]
7648 Enable interrupts for the MMIO based physical layer
7649 for the FIFO interface. By default it is set to false
7650 (0). For more information about TPM hardware interfaces
7651 defined by Trusted Computing Group (TCG) see
7652 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
7653
7654 tp_printk [FTRACE]
7655 Have the tracepoints sent to printk as well as the
7656 tracing ring buffer. This is useful for early boot up
7657 where the system hangs or reboots and does not give the
7658 option for reading the tracing buffer or performing a
7659 ftrace_dump_on_oops.
7660
7661 To turn off having tracepoints sent to printk,
7662 echo 0 > /proc/sys/kernel/tracepoint_printk
7663 Note, echoing 1 into this file without the
7664 tp_printk kernel cmdline option has no effect.
7665
7666 The tp_printk_stop_on_boot (see below) can also be used
7667 to stop the printing of events to console at
7668 late_initcall_sync.
7669
7670 ** CAUTION **
7671
7672 Having tracepoints sent to printk() and activating high
7673 frequency tracepoints such as irq or sched, can cause
7674 the system to live lock.
7675
7676 tp_printk_stop_on_boot [FTRACE]
7677 When tp_printk (above) is set, it can cause a lot of noise
7678 on the console. It may be useful to only include the
7679 printing of events during boot up, as user space may
7680 make the system inoperable.
7681
7682 This command line option will stop the printing of events
7683 to console at the late_initcall_sync() time frame.
7684
7685 trace_buf_size=nn[KMG]
7686 [FTRACE] will set tracing buffer size on each cpu.
7687
7688 trace_clock= [FTRACE] Set the clock used for tracing events
7689 at boot up.
7690 local - Use the per CPU time stamp counter
7691 (converted into nanoseconds). Fast, but
7692 depending on the architecture, may not be
7693 in sync between CPUs.
7694 global - Event time stamps are synchronized across
7695 CPUs. May be slower than the local clock,
7696 but better for some race conditions.
7697 counter - Simple counting of events (1, 2, ..)
7698 note, some counts may be skipped due to the
7699 infrastructure grabbing the clock more than
7700 once per event.
7701 uptime - Use jiffies as the time stamp.
7702 perf - Use the same clock that perf uses.
7703 mono - Use ktime_get_mono_fast_ns() for time stamps.
7704 mono_raw - Use ktime_get_raw_fast_ns() for time
7705 stamps.
7706 boot - Use ktime_get_boot_fast_ns() for time stamps.
7707 Architectures may add more clocks. See
7708 Documentation/trace/ftrace.rst for more details.
7709
7710 trace_event=[event-list]
7711 [FTRACE] Set and start specified trace events in order
7712 to facilitate early boot debugging. The event-list is a
7713 comma-separated list of trace events to enable. See
7714 also Documentation/trace/events.rst
7715
7716 To enable modules, use :mod: keyword:
7717
7718 trace_event=:mod:<module>
7719
7720 The value before :mod: will only enable specific events
7721 that are part of the module. See the above mentioned
7722 document for more information.
7723
7724 trace_instance=[instance-info]
7725 [FTRACE] Create a ring buffer instance early in boot up.
7726 This will be listed in:
7727
7728 /sys/kernel/tracing/instances
7729
7730 Events can be enabled at the time the instance is created
7731 via:
7732
7733 trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
7734
7735 Note, the "<system*>:" portion is optional if the event is
7736 unique.
7737
7738 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
7739
7740 will enable the "sched_switch" event (note, the "sched:" is optional, and
7741 the same thing would happen if it was left off). The irq_handler_entry
7742 event, and all events under the "initcall" system.
7743
7744 Flags can be added to the instance to modify its behavior when it is
7745 created. The flags are separated by '^'.
7746
7747 The available flags are:
7748
7749 traceoff - Have the tracing instance tracing disabled after it is created.
7750 traceprintk - Have trace_printk() write into this trace instance
7751 (note, "printk" and "trace_printk" can also be used)
7752
7753 trace_instance=foo^traceoff^traceprintk,sched,irq
7754
7755 The flags must come before the defined events.
7756
7757 If memory has been reserved (see memmap for x86), the instance
7758 can use that memory:
7759
7760 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M
7761
7762 The above will create a "boot_map" instance that uses the physical
7763 memory at 0x284500000 that is 12Megs. The per CPU buffers of that
7764 instance will be split up accordingly.
7765
7766 Alternatively, the memory can be reserved by the reserve_mem option:
7767
7768 reserve_mem=12M:4096:trace trace_instance=boot_map@trace
7769
7770 This will reserve 12 megabytes at boot up with a 4096 byte alignment
7771 and place the ring buffer in this memory. Note that due to KASLR, the
7772 memory may not be the same location each time, which will not preserve
7773 the buffer content.
7774
7775 Also note that the layout of the ring buffer data may change between
7776 kernel versions where the validator will fail and reset the ring buffer
7777 if the layout is not the same as the previous kernel.
7778
7779 If the ring buffer is used for persistent bootups and has events enabled,
7780 it is recommend to disable tracing so that events from a previous boot do not
7781 mix with events of the current boot (unless you are debugging a random crash
7782 at boot up).
7783
7784 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq
7785
7786 Note, saving the trace buffer across reboots does require that the system
7787 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION
7788 can force a memory reset on boot which will clear any trace that was stored.
7789 This is just one of many ways that can clear memory. Make sure your system
7790 keeps the content of memory across reboots before relying on this option.
7791
7792 NB: Both the mapped address and size must be page aligned for the architecture.
7793
7794 See also Documentation/trace/debugging.rst
7795
7796
7797 trace_options=[option-list]
7798 [FTRACE] Enable or disable tracer options at boot.
7799 The option-list is a comma delimited list of options
7800 that can be enabled or disabled just as if you were
7801 to echo the option name into
7802
7803 /sys/kernel/tracing/trace_options
7804
7805 For example, to enable stacktrace option (to dump the
7806 stack trace of each event), add to the command line:
7807
7808 trace_options=stacktrace
7809
7810 See also Documentation/trace/ftrace.rst "trace options"
7811 section.
7812
7813 trace_trigger=[trigger-list]
7814 [FTRACE] Add an event trigger on specific events.
7815 Set a trigger on top of a specific event, with an optional
7816 filter.
7817
7818 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..."
7819 Where more than one trigger may be specified that are comma delimited.
7820
7821 For example:
7822
7823 trace_trigger="sched_switch.stacktrace if prev_state == 2"
7824
7825 The above will enable the "stacktrace" trigger on the "sched_switch"
7826 event but only trigger it if the "prev_state" of the "sched_switch"
7827 event is "2" (TASK_UNINTERRUPTIBLE).
7828
7829 See also "Event triggers" in Documentation/trace/events.rst
7830
7831
7832 traceoff_after_boot
7833 [FTRACE] Sometimes tracing is used to debug issues
7834 during the boot process. Since the trace buffer has a
7835 limited amount of storage, it may be prudent to
7836 disable tracing after the boot is finished, otherwise
7837 the critical information may be overwritten. With this
7838 option, the main tracing buffer will be turned off at
7839 the end of the boot process.
7840
7841 traceoff_on_warning
7842 [FTRACE] enable this option to disable tracing when a
7843 warning is hit. This turns off "tracing_on". Tracing can
7844 be enabled again by echoing '1' into the "tracing_on"
7845 file located in /sys/kernel/tracing/
7846
7847 This option is useful, as it disables the trace before
7848 the WARNING dump is called, which prevents the trace to
7849 be filled with content caused by the warning output.
7850
7851 This option can also be set at run time via the sysctl
7852 option: kernel/traceoff_on_warning
7853
7854 transparent_hugepage=
7855 [KNL]
7856 Format: [always|madvise|never]
7857 Can be used to control the default behavior of the system
7858 with respect to transparent hugepages.
7859 See Documentation/admin-guide/mm/transhuge.rst
7860 for more details.
7861
7862 transparent_hugepage_shmem= [KNL]
7863 Format: [always|within_size|advise|never|deny|force]
7864 Can be used to control the hugepage allocation policy for
7865 the internal shmem mount.
7866 See Documentation/admin-guide/mm/transhuge.rst
7867 for more details.
7868
7869 transparent_hugepage_tmpfs= [KNL]
7870 Format: [always|within_size|advise|never]
7871 Can be used to control the default hugepage allocation policy
7872 for the tmpfs mount.
7873 See Documentation/admin-guide/mm/transhuge.rst
7874 for more details.
7875
7876 trusted.source= [KEYS]
7877 Format: <string>
7878 This parameter identifies the trust source as a backend
7879 for trusted keys implementation. Supported trust
7880 sources:
7881 - "tpm"
7882 - "tee"
7883 - "caam"
7884 - "dcp"
7885 - "pkwm"
7886 If not specified then it defaults to iterating through
7887 the trust source list starting with TPM and assigns the
7888 first trust source as a backend which is initialized
7889 successfully during iteration.
7890
7891 trusted.rng= [KEYS]
7892 Format: <string>
7893 The RNG used to generate key material for trusted keys.
7894 Can be one of:
7895 - "kernel"
7896 - the same value as trusted.source: "tpm" or "tee"
7897 - "default"
7898 If not specified, "default" is used. In this case,
7899 the RNG's choice is left to each individual trust source.
7900
7901 trusted.dcp_use_otp_key
7902 This is intended to be used in combination with
7903 trusted.source=dcp and will select the DCP OTP key
7904 instead of the DCP UNIQUE key blob encryption.
7905
7906 trusted.dcp_skip_zk_test
7907 This is intended to be used in combination with
7908 trusted.source=dcp and will disable the check if the
7909 blob key is all zeros. This is helpful for situations where
7910 having this key zero'ed is acceptable. E.g. in testing
7911 scenarios.
7912
7913 tsa= [X86] Control mitigation for Transient Scheduler
7914 Attacks on AMD CPUs. Search the following in your
7915 favourite search engine for more details:
7916
7917 "Technical guidance for mitigating transient scheduler
7918 attacks".
7919
7920 off - disable the mitigation
7921 on - enable the mitigation (default)
7922 user - mitigate only user/kernel transitions
7923 vm - mitigate only guest/host transitions
7924
7925
7926 tsc= Disable clocksource stability checks for TSC.
7927 Format: <string>
7928 [x86] reliable: mark tsc clocksource as reliable, this
7929 disables clocksource verification at runtime, as well
7930 as the stability checks done at bootup. Used to enable
7931 high-resolution timer mode on older hardware, and in
7932 virtualized environment.
7933 [x86] noirqtime: Do not use TSC to do irq accounting.
7934 Used to run time disable IRQ_TIME_ACCOUNTING on any
7935 platforms where RDTSC is slow and this accounting
7936 can add overhead.
7937 [x86] unstable: mark the TSC clocksource as unstable, this
7938 marks the TSC unconditionally unstable at bootup and
7939 avoids any further wobbles once the TSC watchdog notices.
7940 [x86] nowatchdog: disable clocksource watchdog. Used
7941 in situations with strict latency requirements (where
7942 interruptions from clocksource watchdog are not
7943 acceptable).
7944 [x86] recalibrate: force recalibration against a HW timer
7945 (HPET or PM timer) on systems whose TSC frequency was
7946 obtained from HW or FW using either an MSR or CPUID(0x15).
7947 Warn if the difference is more than 500 ppm.
7948 [x86] watchdog: Enforce the clocksource watchdog on TSC
7949
7950 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given
7951 value instead. Useful when the early TSC frequency discovery
7952 procedure is not reliable, such as on overclocked systems
7953 with CPUID.16h support and partial CPUID.15h support.
7954 Format: <unsigned int>
7955
7956 tsx= [X86] Control Transactional Synchronization
7957 Extensions (TSX) feature in Intel processors that
7958 support TSX control.
7959
7960 This parameter controls the TSX feature. The options are:
7961
7962 on - Enable TSX on the system. Although there are
7963 mitigations for all known security vulnerabilities,
7964 TSX has been known to be an accelerator for
7965 several previous speculation-related CVEs, and
7966 so there may be unknown security risks associated
7967 with leaving it enabled.
7968
7969 off - Disable TSX on the system. (Note that this
7970 option takes effect only on newer CPUs which are
7971 not vulnerable to MDS, i.e., have
7972 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
7973 the new IA32_TSX_CTRL MSR through a microcode
7974 update. This new MSR allows for the reliable
7975 deactivation of the TSX functionality.)
7976
7977 auto - Disable TSX if X86_BUG_TAA is present,
7978 otherwise enable TSX on the system.
7979
7980 Not specifying this option is equivalent to tsx=off.
7981
7982 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
7983 for more details.
7984
7985 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async
7986 Abort (TAA) vulnerability.
7987
7988 Similar to Micro-architectural Data Sampling (MDS)
7989 certain CPUs that support Transactional
7990 Synchronization Extensions (TSX) are vulnerable to an
7991 exploit against CPU internal buffers which can forward
7992 information to a disclosure gadget under certain
7993 conditions.
7994
7995 In vulnerable processors, the speculatively forwarded
7996 data can be used in a cache side channel attack, to
7997 access data to which the attacker does not have direct
7998 access.
7999
8000 This parameter controls the TAA mitigation. The
8001 options are:
8002
8003 full - Enable TAA mitigation on vulnerable CPUs
8004 if TSX is enabled.
8005
8006 full,nosmt - Enable TAA mitigation and disable SMT on
8007 vulnerable CPUs. If TSX is disabled, SMT
8008 is not disabled because CPU is not
8009 vulnerable to cross-thread TAA attacks.
8010 off - Unconditionally disable TAA mitigation
8011
8012 On MDS-affected machines, tsx_async_abort=off can be
8013 prevented by an active MDS mitigation as both vulnerabilities
8014 are mitigated with the same mechanism so in order to disable
8015 this mitigation, you need to specify mds=off too.
8016
8017 Not specifying this option is equivalent to
8018 tsx_async_abort=full. On CPUs which are MDS affected
8019 and deploy MDS mitigation, TAA mitigation is not
8020 required and doesn't provide any additional
8021 mitigation.
8022
8023 For details see:
8024 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
8025
8026 turbografx.map[2|3]= [HW,JOY]
8027 TurboGraFX parallel port interface
8028 Format:
8029 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
8030 See also Documentation/input/devices/joystick-parport.rst
8031
8032 udbg-immortal [PPC] When debugging early kernel crashes that
8033 happen after console_init() and before a proper
8034 console driver takes over, this boot options might
8035 help "seeing" what's going on.
8036
8037 uhash_entries= [KNL,NET]
8038 Set number of hash buckets for UDP/UDP-Lite connections
8039
8040 uhci-hcd.ignore_oc=
8041 [USB] Ignore overcurrent events (default N).
8042 Some badly-designed motherboards generate lots of
8043 bogus events, for ports that aren't wired to
8044 anything. Set this parameter to avoid log spamming.
8045 Note that genuine overcurrent events won't be
8046 reported either.
8047
8048 unaligned_scalar_speed=
8049 [RISCV]
8050 Format: {slow | fast | unsupported}
8051 Allow skipping scalar unaligned access speed tests. This
8052 is useful for testing alternative code paths and to skip
8053 the tests in environments where they run too slowly. All
8054 CPUs must have the same scalar unaligned access speed.
8055
8056 unaligned_vector_speed=
8057 [RISCV]
8058 Format: {slow | fast | unsupported}
8059 Allow skipping vector unaligned access speed tests. This
8060 is useful for testing alternative code paths and to skip
8061 the tests in environments where they run too slowly. All
8062 CPUs must have the same vector unaligned access speed.
8063
8064 unknown_nmi_panic
8065 [X86] Cause panic on unknown NMI.
8066
8067 unwind_debug [X86-64,EARLY]
8068 Enable unwinder debug output. This can be
8069 useful for debugging certain unwinder error
8070 conditions, including corrupt stacks and
8071 bad/missing unwinder metadata.
8072
8073 usbcore.authorized_default=
8074 [USB] Default USB device authorization:
8075 (default -1 = authorized (same as 1),
8076 0 = not authorized, 1 = authorized, 2 = authorized
8077 if device connected to internal port)
8078
8079 usbcore.autosuspend=
8080 [USB] The autosuspend time delay (in seconds) used
8081 for newly-detected USB devices (default 2). This
8082 is the time required before an idle device will be
8083 autosuspended. Devices for which the delay is set
8084 to a negative value won't be autosuspended at all.
8085
8086 usbcore.usbfs_snoop=
8087 [USB] Set to log all usbfs traffic (default 0 = off).
8088
8089 usbcore.usbfs_snoop_max=
8090 [USB] Maximum number of bytes to snoop in each URB
8091 (default = 65536).
8092
8093 usbcore.blinkenlights=
8094 [USB] Set to cycle leds on hubs (default 0 = off).
8095
8096 usbcore.old_scheme_first=
8097 [USB] Start with the old device initialization
8098 scheme (default 0 = off).
8099
8100 usbcore.usbfs_memory_mb=
8101 [USB] Memory limit (in MB) for buffers allocated by
8102 usbfs (default = 16, 0 = max = 2047).
8103
8104 usbcore.use_both_schemes=
8105 [USB] Try the other device initialization scheme
8106 if the first one fails (default 1 = enabled).
8107
8108 usbcore.initial_descriptor_timeout=
8109 [USB] Specifies timeout for the initial 64-byte
8110 USB_REQ_GET_DESCRIPTOR request in milliseconds
8111 (default 5000 = 5.0 seconds).
8112
8113 usbcore.nousb [USB] Disable the USB subsystem
8114
8115 usbcore.quirks=
8116 [USB] A list of quirk entries to augment the built-in
8117 usb core quirk list. List entries are separated by
8118 commas. Each entry has the form
8119 VendorID:ProductID:Flags. The IDs are 4-digit hex
8120 numbers and Flags is a set of letters. Each letter
8121 will change the built-in quirk; setting it if it is
8122 clear and clearing it if it is set. The letters have
8123 the following meanings:
8124 a = USB_QUIRK_STRING_FETCH_255 (string
8125 descriptors must not be fetched using
8126 a 255-byte read);
8127 b = USB_QUIRK_RESET_RESUME (device can't resume
8128 correctly so reset it instead);
8129 c = USB_QUIRK_NO_SET_INTF (device can't handle
8130 Set-Interface requests);
8131 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
8132 handle its Configuration or Interface
8133 strings);
8134 e = USB_QUIRK_RESET (device can't be reset
8135 (e.g morph devices), don't use reset);
8136 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
8137 more interface descriptions than the
8138 bNumInterfaces count, and can't handle
8139 talking to these interfaces);
8140 g = USB_QUIRK_DELAY_INIT (device needs a pause
8141 during initialization, after we read
8142 the device descriptor);
8143 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
8144 high speed and super speed interrupt
8145 endpoints, the USB 2.0 and USB 3.0 spec
8146 require the interval in microframes (1
8147 microframe = 125 microseconds) to be
8148 calculated as interval = 2 ^
8149 (bInterval-1).
8150 Devices with this quirk report their
8151 bInterval as the result of this
8152 calculation instead of the exponent
8153 variable used in the calculation);
8154 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
8155 handle device_qualifier descriptor
8156 requests);
8157 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
8158 generates spurious wakeup, ignore
8159 remote wakeup capability);
8160 k = USB_QUIRK_NO_LPM (device can't handle Link
8161 Power Management);
8162 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
8163 (Device reports its bInterval as linear
8164 frames instead of the USB 2.0
8165 calculation);
8166 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
8167 to be disconnected before suspend to
8168 prevent spurious wakeup);
8169 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
8170 pause after every control message);
8171 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
8172 delay after resetting its port);
8173 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT
8174 (Reduce timeout of the SET_ADDRESS
8175 request from 5000 ms to 500 ms);
8176 q = USB_QUIRK_FORCE_ONE_CONFIG (Device
8177 claims zero configurations,
8178 forcing to 1);
8179 Example: quirks=0781:5580:bk,0a5c:5834:gij
8180
8181 usbhid.mousepoll=
8182 [USBHID] The interval which mice are to be polled at.
8183
8184 usbhid.jspoll=
8185 [USBHID] The interval which joysticks are to be polled at.
8186
8187 usbhid.kbpoll=
8188 [USBHID] The interval which keyboards are to be polled at.
8189
8190 usb-storage.delay_use=
8191 [UMS] The delay in seconds before a new device is
8192 scanned for Logical Units (default 1).
8193 Optionally the delay in milliseconds if the value has
8194 suffix with "ms".
8195 Example: delay_use=2567ms
8196
8197 usb-storage.quirks=
8198 [UMS] A list of quirks entries to supplement or
8199 override the built-in unusual_devs list. List
8200 entries are separated by commas. Each entry has
8201 the form VID:PID:Flags where VID and PID are Vendor
8202 and Product ID values (4-digit hex numbers) and
8203 Flags is a set of characters, each corresponding
8204 to a common usb-storage quirk flag as follows:
8205 a = SANE_SENSE (collect more than 18 bytes
8206 of sense data, not on uas);
8207 b = BAD_SENSE (don't collect more than 18
8208 bytes of sense data, not on uas);
8209 c = FIX_CAPACITY (decrease the reported
8210 device capacity by one sector);
8211 d = NO_READ_DISC_INFO (don't use
8212 READ_DISC_INFO command, not on uas);
8213 e = NO_READ_CAPACITY_16 (don't use
8214 READ_CAPACITY_16 command);
8215 f = NO_REPORT_OPCODES (don't use report opcodes
8216 command, uas only);
8217 g = MAX_SECTORS_240 (don't transfer more than
8218 240 sectors at a time, uas only);
8219 h = CAPACITY_HEURISTICS (decrease the
8220 reported device capacity by one
8221 sector if the number is odd);
8222 i = IGNORE_DEVICE (don't bind to this
8223 device);
8224 j = NO_REPORT_LUNS (don't use report luns
8225 command, uas only);
8226 k = NO_SAME (do not use WRITE_SAME, uas only)
8227 l = NOT_LOCKABLE (don't try to lock and
8228 unlock ejectable media, not on uas);
8229 m = MAX_SECTORS_64 (don't transfer more
8230 than 64 sectors = 32 KB at a time,
8231 not on uas);
8232 n = INITIAL_READ10 (force a retry of the
8233 initial READ(10) command, not on uas);
8234 o = CAPACITY_OK (accept the capacity
8235 reported by the device, not on uas);
8236 p = WRITE_CACHE (the device cache is ON
8237 by default, not on uas);
8238 r = IGNORE_RESIDUE (the device reports
8239 bogus residue values, not on uas);
8240 s = SINGLE_LUN (the device has only one
8241 Logical Unit);
8242 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
8243 commands, uas only);
8244 u = IGNORE_UAS (don't bind to the uas driver);
8245 w = NO_WP_DETECT (don't test whether the
8246 medium is write-protected).
8247 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
8248 even if the device claims no cache,
8249 not on uas)
8250 Example: quirks=0419:aaf5:rl,0421:0433:rc
8251
8252 user_debug= [KNL,ARM]
8253 Format: <int>
8254 See arch/arm/Kconfig.debug help text.
8255 1 - undefined instruction events
8256 2 - system calls
8257 4 - invalid data aborts
8258 8 - SIGSEGV faults
8259 16 - SIGBUS faults
8260 Example: user_debug=31
8261
8262 vdso= [X86,SH,SPARC]
8263 On X86_32, this is an alias for vdso32=. Otherwise:
8264
8265 vdso=1: enable VDSO (the default)
8266 vdso=0: disable VDSO mapping
8267
8268 vdso32= [X86] Control the 32-bit vDSO
8269 vdso32=1: enable 32-bit VDSO
8270 vdso32=0 or vdso32=2: disable 32-bit VDSO
8271
8272 See the help text for CONFIG_COMPAT_VDSO for more
8273 details. If CONFIG_COMPAT_VDSO is set, the default is
8274 vdso32=0; otherwise, the default is vdso32=1.
8275
8276 For compatibility with older kernels, vdso32=2 is an
8277 alias for vdso32=0.
8278
8279 Try vdso32=0 if you encounter an error that says:
8280 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
8281
8282 video= [FB,EARLY] Frame buffer configuration
8283 See Documentation/fb/modedb.rst.
8284
8285 video.brightness_switch_enabled= [ACPI]
8286 Format: [0|1]
8287 If set to 1, on receiving an ACPI notify event
8288 generated by hotkey, video driver will adjust brightness
8289 level and then send out the event to user space through
8290 the allocated input device. If set to 0, video driver
8291 will only send out the event without touching backlight
8292 brightness level.
8293 default: 1
8294
8295 virtio_mmio.device=
8296 [VMMIO] Memory mapped virtio (platform) device.
8297
8298 <size>@<baseaddr>:<irq>[:<id>]
8299 where:
8300 <size> := size (can use standard suffixes
8301 like K, M and G)
8302 <baseaddr> := physical base address
8303 <irq> := interrupt number (as passed to
8304 request_irq())
8305 <id> := (optional) platform device id
8306 example:
8307 virtio_mmio.device=1K@0x100b0000:48:7
8308
8309 Can be used multiple times for multiple devices.
8310
8311 vga= [BOOT,X86-32] Select a particular video mode
8312 See Documentation/arch/x86/boot.rst and
8313 Documentation/admin-guide/svga.rst.
8314 Use vga=ask for menu.
8315 This is actually a boot loader parameter; the value is
8316 passed to the kernel using a special protocol.
8317
8318 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
8319 May slow down system boot speed, especially when
8320 enabled on systems with a large amount of memory.
8321 All options are enabled by default, and this
8322 interface is meant to allow for selectively
8323 enabling or disabling specific virtual memory
8324 debugging features.
8325
8326 Available options are:
8327 P Enable page structure init time poisoning
8328 - Disable all of the above options
8329
8330 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an
8331 exact size of <nn>. This can be used to increase
8332 the minimum size (128MB on x86, arm32 platforms).
8333 It can also be used to decrease the size and leave more room
8334 for directly mapped kernel RAM. Note that this parameter does
8335 not exist on many other platforms (including arm64, alpha,
8336 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc,
8337 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc).
8338
8339 vmcp_cma=nn[MG] [KNL,S390,EARLY]
8340 Sets the memory size reserved for contiguous memory
8341 allocations for the vmcp device driver.
8342
8343 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
8344 Format: <command>
8345
8346 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
8347 Format: <command>
8348
8349 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
8350 Format: <command>
8351
8352 vmscape= [X86] Controls mitigation for VMscape attacks.
8353 VMscape attacks can leak information from a userspace
8354 hypervisor to a guest via speculative side-channels.
8355
8356 off - disable the mitigation
8357 ibpb - use Indirect Branch Prediction Barrier
8358 (IBPB) mitigation (default)
8359 force - force vulnerability detection even on
8360 unaffected processors
8361
8362 vsyscall= [X86-64,EARLY]
8363 Controls the behavior of vsyscalls (i.e. calls to
8364 fixed addresses of 0xffffffffff600x00 from legacy
8365 code). Most statically-linked binaries and older
8366 versions of glibc use these calls. Because these
8367 functions are at fixed addresses, they make nice
8368 targets for exploits that can control RIP.
8369
8370 emulate Vsyscalls turn into traps and are emulated
8371 reasonably safely. The vsyscall page is
8372 readable. This disables the Linear
8373 Address Space Separation (LASS) security
8374 feature and makes the system less secure.
8375
8376 xonly [default] Vsyscalls turn into traps and are
8377 emulated reasonably safely. The vsyscall
8378 page is not readable.
8379
8380 none Vsyscalls don't work at all. This makes
8381 them quite hard to use for exploits but
8382 might break your system.
8383
8384 vt.color= [VT] Default text color.
8385 Format: 0xYX, X = foreground, Y = background.
8386 Default: 0x07 = light gray on black.
8387
8388 vt.cur_default= [VT] Default cursor shape.
8389 Format: 0xCCBBAA, where AA, BB, and CC are the same as
8390 the parameters of the <Esc>[?A;B;Cc escape sequence;
8391 see vga-softcursor.rst. Default: 2 = underline.
8392
8393 vt.default_blu= [VT]
8394 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
8395 Change the default blue palette of the console.
8396 This is a 16-member array composed of values
8397 ranging from 0-255.
8398
8399 vt.default_grn= [VT]
8400 Format: <green0>,<green1>,<green2>,...,<green15>
8401 Change the default green palette of the console.
8402 This is a 16-member array composed of values
8403 ranging from 0-255.
8404
8405 vt.default_red= [VT]
8406 Format: <red0>,<red1>,<red2>,...,<red15>
8407 Change the default red palette of the console.
8408 This is a 16-member array composed of values
8409 ranging from 0-255.
8410
8411 vt.default_utf8=
8412 [VT]
8413 Format=<0|1>
8414 Set system-wide default UTF-8 mode for all tty's.
8415 Default is 1, i.e. UTF-8 mode is enabled for all
8416 newly opened terminals.
8417
8418 vt.global_cursor_default=
8419 [VT]
8420 Format=<-1|0|1>
8421 Set system-wide default for whether a cursor
8422 is shown on new VTs. Default is -1,
8423 i.e. cursors will be created by default unless
8424 overridden by individual drivers. 0 will hide
8425 cursors, 1 will display them.
8426
8427 vt.italic= [VT] Default color for italic text; 0-15.
8428 Default: 2 = green.
8429
8430 vt.underline= [VT] Default color for underlined text; 0-15.
8431 Default: 3 = cyan.
8432
8433 watchdog timers [HW,WDT] For information on watchdog timers,
8434 see Documentation/watchdog/watchdog-parameters.rst
8435 or other driver-specific files in the
8436 Documentation/watchdog/ directory.
8437
8438 watchdog_thresh=
8439 [KNL]
8440 Set the hard lockup detector stall duration
8441 threshold in seconds. The soft lockup detector
8442 threshold is set to twice the value. A value of 0
8443 disables both lockup detectors. Default is 10
8444 seconds.
8445
8446 workqueue.unbound_cpus=
8447 [KNL,SMP] Specify to constrain one or some CPUs
8448 to use in unbound workqueues.
8449 Format: <cpu-list>
8450 By default, all online CPUs are available for
8451 unbound workqueues.
8452
8453 workqueue.watchdog_thresh=
8454 If CONFIG_WQ_WATCHDOG is configured, workqueue can
8455 warn stall conditions and dump internal state to
8456 help debugging. 0 disables workqueue stall
8457 detection; otherwise, it's the stall threshold
8458 duration in seconds. The default value is 30 and
8459 it can be updated at runtime by writing to the
8460 corresponding sysfs file.
8461
8462 workqueue.panic_on_stall=<uint>
8463 Panic when workqueue stall is detected by
8464 CONFIG_WQ_WATCHDOG. It sets the number times of the
8465 stall to trigger panic.
8466
8467 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC,
8468 which is 0 (disabled) if not configured.
8469
8470 workqueue.panic_on_stall_time=<uint>
8471 Panic when a workqueue stall has been continuous for
8472 the specified number of seconds. Unlike panic_on_stall
8473 which counts accumulated stall events, this triggers
8474 based on the duration of a single continuous stall.
8475
8476 The default is 0, which disables the time-based panic.
8477
8478 workqueue.cpu_intensive_thresh_us=
8479 Per-cpu work items which run for longer than this
8480 threshold are automatically considered CPU intensive
8481 and excluded from concurrency management to prevent
8482 them from noticeably delaying other per-cpu work
8483 items. Default is 10000 (10ms).
8484
8485 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
8486 will report the work functions which violate this
8487 threshold repeatedly. They are likely good
8488 candidates for using WQ_UNBOUND workqueues instead.
8489
8490 workqueue.cpu_intensive_warning_thresh=<uint>
8491 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
8492 will report the work functions which violate the
8493 intensive_threshold_us repeatedly. In order to prevent
8494 spurious warnings, start printing only after a work
8495 function has violated this threshold number of times.
8496
8497 The default is 4 times. 0 disables the warning.
8498
8499 workqueue.power_efficient
8500 Per-cpu workqueues are generally preferred because
8501 they show better performance thanks to cache
8502 locality; unfortunately, per-cpu workqueues tend to
8503 be more power hungry than unbound workqueues.
8504
8505 Enabling this makes the per-cpu workqueues which
8506 were observed to contribute significantly to power
8507 consumption unbound, leading to measurably lower
8508 power usage at the cost of small performance
8509 overhead.
8510
8511 The default value of this parameter is determined by
8512 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
8513
8514 workqueue.default_affinity_scope=
8515 Select the default affinity scope to use for unbound
8516 workqueues. Can be one of "cpu", "smt", "cache",
8517 "cache_shard", "numa" and "system". Default is
8518 "cache_shard". For more
8519 information, see the Affinity Scopes section in
8520 Documentation/core-api/workqueue.rst.
8521
8522 This can be changed after boot by writing to the
8523 matching /sys/module/workqueue/parameters file. All
8524 workqueues with the "default" affinity scope will be
8525 updated accordingly.
8526
8527 workqueue.debug_force_rr_cpu
8528 Workqueue used to implicitly guarantee that work
8529 items queued without explicit CPU specified are put
8530 on the local CPU. This guarantee is no longer true
8531 and while local CPU is still preferred work items
8532 may be put on foreign CPUs. This debug option
8533 forces round-robin CPU selection to flush out
8534 usages which depend on the now broken guarantee.
8535 When enabled, memory and cache locality will be
8536 impacted.
8537
8538 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access
8539 Type) of ioremap_wc().
8540
8541 on - Enable writecombine, use WUC for ioremap_wc()
8542 off - Disable writecombine, use SUC for ioremap_wc()
8543
8544 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of
8545 default x2apic cluster mode on platforms
8546 supporting x2apic.
8547
8548 xen_512gb_limit [KNL,X86-64,XEN]
8549 Restricts the kernel running paravirtualized under Xen
8550 to use only up to 512 GB of RAM. The reason to do so is
8551 crash analysis tools and Xen tools for doing domain
8552 save/restore/migration must be enabled to handle larger
8553 domains.
8554
8555 xen_console_io [XEN,EARLY]
8556 Boolean option to enable/disable the usage of the Xen
8557 console_io hypercalls to read and write to the console.
8558 Mostly useful for debugging and development.
8559
8560 xen_emul_unplug= [HW,X86,XEN,EARLY]
8561 Unplug Xen emulated devices
8562 Format: [unplug0,][unplug1]
8563 ide-disks -- unplug primary master IDE devices
8564 aux-ide-disks -- unplug non-primary-master IDE devices
8565 nics -- unplug network devices
8566 all -- unplug all emulated devices (NICs and IDE disks)
8567 unnecessary -- unplugging emulated devices is
8568 unnecessary even if the host did not respond to
8569 the unplug protocol
8570 never -- do not unplug even if version check succeeds
8571
8572 xen_legacy_crash [X86,XEN,EARLY]
8573 Crash from Xen panic notifier, without executing late
8574 panic() code such as dumping handler.
8575
8576 xen_mc_debug [X86,XEN,EARLY]
8577 Enable multicall debugging when running as a Xen PV guest.
8578 Enabling this feature will reduce performance a little
8579 bit, so it should only be enabled for obtaining extended
8580 debug data in case of multicall errors.
8581
8582 xen_msr_safe= [X86,XEN,EARLY]
8583 Format: <bool>
8584 Select whether to always use non-faulting (safe) MSR
8585 access functions when running as Xen PV guest. The
8586 default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
8587
8588 xen_nopv [X86]
8589 Disables the PV optimizations forcing the HVM guest to
8590 run as generic HVM guest with no PV drivers.
8591 This option is obsoleted by the "nopv" option, which
8592 has equivalent effect for XEN platform.
8593
8594 xen_no_vector_callback
8595 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen
8596 event channel interrupts.
8597
8598 xen_scrub_pages= [XEN]
8599 Boolean option to control scrubbing pages before giving them back
8600 to Xen, for use by other domains. Can be also changed at runtime
8601 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
8602 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
8603
8604 xen_timer_slop= [X86-64,XEN,EARLY]
8605 Set the timer slop (in nanoseconds) for the virtual Xen
8606 timers (default is 100000). This adjusts the minimum
8607 delta of virtualized Xen timers, where lower values
8608 improve timer resolution at the expense of processing
8609 more timer interrupts.
8610
8611 xen.balloon_boot_timeout= [XEN]
8612 The time (in seconds) to wait before giving up to boot
8613 in case initial ballooning fails to free enough memory.
8614 Applies only when running as HVM or PVH guest and
8615 started with less memory configured than allowed at
8616 max. Default is 180.
8617
8618 xen.event_eoi_delay= [XEN]
8619 How long to delay EOI handling in case of event
8620 storms (jiffies). Default is 10.
8621
8622 xen.event_loop_timeout= [XEN]
8623 After which time (jiffies) the event handling loop
8624 should start to delay EOI handling. Default is 2.
8625
8626 xen.fifo_events= [XEN]
8627 Boolean parameter to disable using fifo event handling
8628 even if available. Normally fifo event handling is
8629 preferred over the 2-level event handling, as it is
8630 fairer and the number of possible event channels is
8631 much higher. Default is on (use fifo events).
8632
8633 xirc2ps_cs= [NET,PCMCIA]
8634 Format:
8635 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
8636
8637 xive= [PPC]
8638 By default on POWER9 and above, the kernel will
8639 natively use the XIVE interrupt controller. This option
8640 allows the fallback firmware mode to be used:
8641
8642 off Fallback to firmware control of XIVE interrupt
8643 controller on both pseries and powernv
8644 platforms. Only useful on POWER9 and above.
8645
8646 xive.store-eoi=off [PPC]
8647 By default on POWER10 and above, the kernel will use
8648 stores for EOI handling when the XIVE interrupt mode
8649 is active. This option allows the XIVE driver to use
8650 loads instead, as on POWER9.
8651
8652 xhci-hcd.quirks [USB,KNL]
8653 A hex value specifying bitmask with supplemental xhci
8654 host controller quirks. Meaning of each bit can be
8655 consulted in header drivers/usb/host/xhci.h.
8656
8657 xmon [PPC,EARLY]
8658 Format: { early | on | rw | ro | off }
8659 Controls if xmon debugger is enabled. Default is off.
8660 Passing only "xmon" is equivalent to "xmon=early".
8661 early Call xmon as early as possible on boot; xmon
8662 debugger is called from setup_arch().
8663 on xmon debugger hooks will be installed so xmon
8664 is only called on a kernel crash. Default mode,
8665 i.e. either "ro" or "rw" mode, is controlled
8666 with CONFIG_XMON_DEFAULT_RO_MODE.
8667 rw xmon debugger hooks will be installed so xmon
8668 is called only on a kernel crash, mode is write,
8669 meaning SPR registers, memory and, other data
8670 can be written using xmon commands.
8671 ro same as "rw" option above but SPR registers,
8672 memory, and other data can't be written using
8673 xmon commands.
8674 off xmon is disabled.