ionice(1) — Linux manual page


IONICE(1)                     User Commands                    IONICE(1)

NAME         top

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

SYNOPSIS         top

       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         top

       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

       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

           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

           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).

           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         top

       -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
           Print version and exit.

NOTES         top

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

EXAMPLES         top

       •   # 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

AUTHORS         top

       Jens Axboe <>, Karel Zak <>

SEE ALSO         top


REPORTING BUGS         top

       For bug reports, use the issue tracker at

AVAILABILITY         top

       The ionice command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <>. This page
       is part of the util-linux (a random collection of Linux
       utilities) project. Information about the project can be found at
       ⟨⟩. If you have
       a bug report for this manual page, send it to This page was obtained from the
       project's upstream Git repository
       ⟨git://⟩ on
       2023-12-22. (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-14.) If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page,
       or you have corrections or improvements to the information in
       this COLOPHON (which is not part of the original manual page),
       send a mail to

util-linux 2.39.594-1e0ad      2023-07-19                      IONICE(1)

Pages that refer to this page: ioprio_set(2)btrfs-scrub(8)iotop(8)