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

       •   # 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 <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/>.