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

       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).

              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

              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.

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

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

       -V, --version
              Display version information 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


AVAILABILITY         top

       The ionice command is part of the util-linux package and is
       available from

COLOPHON         top

       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
       2021-03-21.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-19.)  If you
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       manual page), send a mail to

util-linux                      July 2011                      IONICE(1)

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