ionice(1)                                                                                                              ionice(1)



NAME
       ionice - get/set program io scheduling class and priority

SYNOPSIS
       ionice [[-c class] [-n classdata] [-t]] -p PID [PID]...
       ionice [-c class] [-n classdata] [-t] COMMAND [ARG]...

DESCRIPTION
       This  program sets or gets the io scheduling class and priority for a program.  If no arguments or just -p is given, ion-
       ice will query the current io scheduling class and priority for that process.

       As of this writing, a process can be in one of three scheduling classes:

       Idle   A program running with idle io priority will only get disk time when no other program has asked for disk io for  a
              defined  grace  period.  The impact of idle io processes 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 io priority.  This class
              takes a priority argument from 0-7, with 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 io priority formally uses "none" as scheduling
              class, but the io 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 CFQ io scheduler a process that has not asked for an io priority inherits CPU sched-
              uling class.  The io priority is derived from the cpu nice level of the process (same as before kernel 2.6.26).


       Real time
              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
              The scheduling class. 0 for none, 1 for real time, 2 for best-effort, 3 for idle.

       -n classdata
              The scheduling class data. This defines the class data, if the class accepts an argument. For real time and  best-
              effort, 0-7 is valid data.

       -p pid Pass in process PID(s) to view or change already running processes. If this argument is not given, ionice will run
              the listed program with the given parameters.

       -t     Ignore failure to set requested priority. If COMMAND or PID(s) is specified, run it even in case it was not possi-
              ble to set desired scheduling priority, what can happen due to insufficient privilegies or old kernel version.

EXAMPLES
       # ionice -c 3 -p 89

       Sets process with PID 89 as an idle io 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.

NOTES
       Linux supports io scheduling priorities and classes since 2.6.13 with the CFQ io scheduler.

AUTHORS
       Jens Axboe <jensATaxboe.dk>

AVAILABILITY
       The  ionice command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-
       linux-ng/.



ionice                                                     August 2005                                                 ionice(1)