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.

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

EXAMPLES
       o   # ionice -c 3 -p 89

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

       o   # ionice -c 2 -n 0 bash

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

       o   # ionice -p 89 91

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

AUTHORS
       Jens Axboe <jens@axboe.dk>, Karel Zak <kzak@redhat.com>

SEE ALSO
       ioprio_set(2)

REPORTING BUGS
       For bug reports, use the issue tracker at
       https://github.com/karelzak/util-linux/issues.

AVAILABILITY
       The ionice command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.37.2                 2021-06-02                         IONICE(1)