ionice man page on CentOS

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ionice(1)							     ionice(1)

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

SYNOPSIS
       ionice [-c] [-n] [-p] [COMMAND [ARG...]]

DESCRIPTION
       This  program  sets the io scheduling class and priority for a program.
       As of this writing, Linux supports 3 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.

       Best effort.  This is the default scheduling class for any process that
       hasn't asked for a specific io priority. Programs inherit the CPU  nice
       setting	for  io	 priorities. 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.

       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 win‐
       dow.

       If no arguments or just -p is given, ionice will query the  current  io
       scheduling class and priority for that process.

OPTIONS
       -c     The  scheduling class. 1 for real time, 2 for best-effort, 3 for
	      idle.

       -n     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     Pass in a process pid to change an already running  process.  If
	      this  argument  is not given, ionice will run the listed program
	      with the given parameters.

EXAMPLES
       # ionice -c3 -p89

       Sets process with PID 89 as an idle io process.

       # ionice -c2 -n0 bash

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

       # ionice -p89

       Returns the class and priority of the process with PID 89.

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

AUTHORS
       Jens Axboe <axboe@suse.de>

ionice				  August 2005			     ionice(1)
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