Manual: ionice

IONICE(1)						User Commands						   IONICE(1)

NAME
       ionice - set or get process I/O scheduling class and priority

SYNOPSIS
       ionice [-c class] [-n level] [-t] -p PID

       ionice [-c class] [-n level] [-t] -P PGID

       ionice [-c class] [-n level] [-t] -u UID

       ionice [-c class] [-n level] [-t] command [argument] ...

DESCRIPTION
       This program sets or gets the I/O scheduling class and priority for a program. If no arguments or just -p is given,
       ionice will query the current I/O scheduling class and priority for that process.

       When command is given, ionice will run this command with the given arguments. If no class is specified, then command
       will be executed with the "best-effort" scheduling class. The default priority level is 4.

       As of this writing, a process can be in one of three scheduling classes:

       Idle
	   A program running with idle I/O priority will only get disk time when no other program has asked for disk I/O for
	   a defined grace period. The impact of an idle I/O process on normal system activity should be zero. This
	   scheduling class does not take a priority argument. Presently, this scheduling class is permitted for an ordinary
	   user (since kernel 2.6.25).

       Best-effort
	   This is the effective scheduling class for any process that has not asked for a specific I/O priority. This class
	   takes a priority argument from 0-7, with a lower number being higher priority. Programs running at the same
	   best-effort priority are served in a round-robin fashion.

	   Note that before kernel 2.6.26 a process that has not asked for an I/O priority formally uses "none" as
	   scheduling class, but the I/O scheduler will treat such processes as if it were in the best-effort class. The
	   priority within the best-effort class will be dynamically derived from the CPU nice level of the process:
	   io_priority = (cpu_nice + 20) / 5.

	   For kernels after 2.6.26 with the CFQ I/O scheduler, a process that has not asked for an I/O priority inherits
	   its CPU scheduling class. The I/O priority is derived from the CPU nice level of the process (same as before
	   kernel 2.6.26).

       Realtime
	   The RT scheduling class is given first access to the disk, regardless of what else is going on in the system.
	   Thus the RT class needs to be used with some care, as it can starve other processes. As with the best-effort
	   class, 8 priority levels are defined denoting how big a time slice a given process will receive on each
	   scheduling window. This scheduling class is not permitted for an ordinary (i.e., non-root) user.

OPTIONS
       -c, --class class
	   Specify the name or number of the scheduling class to use; 0 for none, 1 for realtime, 2 for best-effort, 3 for
	   idle.

       -n, --classdata level
	   Specify the scheduling class data. This only has an effect if the class accepts an argument. For realtime and
	   best-effort, 0-7 are valid data (priority levels), and 0 represents the highest priority level.

       -p, --pid PID...
	   Specify the process IDs of running processes for which to get or set the scheduling parameters.

       -P, --pgid PGID...
	   Specify the process group IDs of running processes for which to get or set the scheduling parameters.

       -t, --ignore
	   Ignore failure to set the requested priority. If command was specified, run it even in case it was not possible
	   to set the desired scheduling priority, which can happen due to insufficient privileges or an old kernel version.

       -u, --uid UID...
	   Specify the user IDs of running processes for which to get or set the scheduling parameters.

       -h, --help
	   Display help text and exit.

       -V, --version
	   Display version and exit.

NOTES
       Linux supports I/O scheduling priorities and classes since 2.6.13 with the CFQ I/O scheduler.

EXAMPLES
       •   # ionice -c 3 -p 89

       Sets process with PID 89 as an idle I/O process.

       •   # ionice -c 2 -n 0 bash

       Runs 'bash' as a best-effort program with highest priority.

       •   # ionice -p 89 91

       Prints the class and priority of the processes with PID 89 and 91.

AUTHORS
       Jens Axboe , Karel Zak 

SEE ALSO
       ioprio_set(2)

REPORTING BUGS
       For bug reports, use the issue tracker .

AVAILABILITY
       The ionice command is part of the util-linux package which can be downloaded from Linux Kernel Archive
       .

util-linux 2.41.3					 2025-12-15						   IONICE(1)