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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] 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 pri-
       ority 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 pro-
	      gram 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 real-
	      time, 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).

       -p, --pid PID...
	      Specify the process 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 and exit.

       -V, --version
	      Display version information and exit.

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.

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

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

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

util-linux				    July 2011					IONICE(1)
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