De-prioritizing a systemd-run job
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README.md
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README.md
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# gentle.sh
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Run commands with limited system resources to prevent builds from hammering system responsiveness.
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## Table of Contents
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- [Background](#background)
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- [Install](#install)
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- [Usage](#usage)
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- [Resource Limits](#resource-limits)
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- [Examples](#examples)
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## Background
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When running large builds or heavy computational workloads, system responsiveness can suffer. `gentle.sh` wraps any command in a systemd-run scope with aggressive resource limits to keep your system usable while the build runs.
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## Install
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Either add to PATH:
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```sh
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export PATH=$(pwd):$PATH
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```
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Or symlink
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```sh
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sudo ln -s $(pwd)/gentle.sh /usr/local/bin
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```
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## Usage
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```bash
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gentle.sh <command> [args...]
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```
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## Resource Limits
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The following resource controls are applied to all commands run through `gentle.sh`:
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### CPU Limits
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- **CPU Affinity**: All CPUs except the first 2 (keeps cores 0-1 free for system)
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- **CPU Scheduling Policy**: `batch` - lower priority than normal processes
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- Available lower option: `idle` - only runs when nothing else needs CPU
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- **CPU Weight**: `1` - minimum weight (1-10000 range)
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- **CPU Quota Period**: `300ms` - period for quota measurement
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- **Nice Level**: `19` - lowest nice priority
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### I/O Limits
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- **IO Weight**: `1` - minimum weight (1-10000 range)
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- **IO Scheduling Class**: `best-effort` with priority `7` - lowest best-effort priority
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- Available lower option: `idle` - lowest possible IO priority
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- **IO Device Latency**: `infinity` applied to all detected block devices - no strict latency enforcement on any drive
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### Memory Limits
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- **MemoryMax**: `80%` - cap at 80% of system memory
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- **TasksMax**: `infinity` - unlimited processes
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## Examples
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Build a large project without freezing your system:
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```bash
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gentle.sh make -j8
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```
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Run a compilation:
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```bash
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gentle.sh ./build.sh
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```
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## Notes
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- The script uses `systemd-run --scope --user`, which requires systemd user sessions
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- Block devices are auto-detected using `lsblk` and IO latency targets are set for all drives
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- The process runs in the foreground (not detached as a service)
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- All resource limits are applied to the process and its children
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gentle.sh
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gentle.sh
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#!/bin/bash
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# Run a command gently with limited CPU, IO, and nice values using systemd-run
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# Calculate CPU affinity (all CPUs except first 2)
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CPU_COUNT=$(nproc)
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CPU_AFFINITY="2-$(($CPU_COUNT - 1))"
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# Get all base block devices to set IO latency target on all drives
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BLOCK_DEVICES=$(lsblk -d -n -o NAME | grep -E "^(nvme|sd)")
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# Build systemd-run command
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# Note: IOSchedulingClass=idle is even lower priority than best-effort
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# Note: CPUSchedulingPolicy=idle is even lower priority than batch
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RUN_CMD=(
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systemd-run
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--scope
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--user
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--nice=19
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--io-weight=1
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--cpu-affinity="$CPU_AFFINITY"
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--property=CPUWeight=1
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--property=MemoryMax=80%
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--property=TasksMax=infinity
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--property=CPUQuotaPeriodSec=300ms
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--property=IOSchedulingClass=best-effort
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--property=IOSchedulingPriority=7
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--property=CPUSchedulingPolicy=batch
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)
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# Add IODeviceLatencyTargetSec for each block device
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for device in $BLOCK_DEVICES; do
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RUN_CMD+=("--property=IODeviceLatencyTargetSec=/dev/$device 20s")
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done
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# Add the command to run
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RUN_CMD+=("$@")
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# Execute
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"${RUN_CMD[@]}"