ionice man page on Ubuntu

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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, ionice  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	activ‐
	      ity should be zero. This scheduling class does not take a prior‐
	      ity 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 prior‐
	      ity  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 scheduling 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  pro‐
	      cesses.  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 possible 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 <jens@axboe.dk>

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

ionice				  August 2005			     ionice(1)
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