IONICE(1)                         User Commands                        IONICE(1)

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

       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...]

       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).

              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.

       -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.

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

       # 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.

       Jens Axboe <>
       Karel Zak <>


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

util-linux                          July 2011                          IONICE(1)