ionice

Run a command with the given scheduling class and priority

Set I/O scheduling class of a running process with a specific [p]id, [P]gid, or [u]id
Run a command with custom I/O scheduling class and priority
Ignore failure to set the requested priority
Run the command even in case it was not possible to set the desired priority (this can happen due to insufficient privileges or an old kernel version)
Print the I/O scheduling class and priority of a running process

ionice [-c class] [-n level] [-t] -p PID...
ionice [-c class] [-n level] [-t] COMMAND [ARG...]

-c, --class=class
    Set I/O class: 0(none), 1(realtime), 2(best-effort, default), 3(idle); or names realtime, best-effort, idle

-n, --classdata=level
    Set priority level 0-7 (0 highest); ignored for idle class

-p, --pid=PID...
    Target existing process ID(s)

-t, --ignore
    Ignore errors setting target class (e.g., non-root realtime)

-h, --help
    Display usage help

-V, --version
    Output version information

The ionice command manages the I/O priority and scheduling class of Linux processes, influencing how disk I/O operations are handled by the kernel's I/O scheduler, primarily CFQ (Completely Fair Queuing) or compatible schedulers like BFQ. It allows users to prioritize I/O requests to ensure critical tasks get preferential access to block devices, preventing low-priority jobs from starving high-priority ones.

Processes are assigned to one of three I/O classes:

• Realtime (1): Highest priority; I/O requests serviced first, levels 0-7 (0 best).
• Best-effort (2): Default class; fair sharing with priority levels 0-7 (0 highest).
• Idle (3): Lowest priority; I/O only when idle, no level needed.

Class 0 reverts to kernel default (usually best-effort).

Use -p PID to adjust running processes or invoke a command directly for new ones. Without arguments, it displays the current shell process's I/O class and priority. This is useful for batch jobs, backups, or multimedia to avoid I/O contention. Root privileges are typically required for realtime class or modifying other users' processes. Modern kernels extend support beyond CFQ, but effectiveness varies by scheduler and workload.

Requires CFQ/BFQ-like I/O scheduler; ineffective with noop/deadline. Root needed for realtime class or foreign PIDs. Levels apply per-task; cgroup overrides possible. No effect on non-block I/O.

ionice -c 3 dd if=/dev/zero of=bigfile bs=1M
Run dd as idle class.

ionice -c 1 -n 0 -p $(pidof mysqld)
Set realtime I/O priority 0 for MySQL.

Run ionice without args to print shell's class/priority: e.g., "best-effort: prio 4".

Added in Linux 2.6.13 (2005) by Balbir Singh; part of util-linux since v2.13. Kernel I/O scheduler interface stabilized later.

nice(1), renice(1), chrt(1), ioprio_get(1)