ionice man page on ElementaryOS

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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 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 permit‐
	      ted 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 pri‐
	      ority argument from 0-7, with a lower number being higher prior‐
	      ity.   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 schedul‐
	      ing  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 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).

       -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  insuffi‐
	      cient 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 scheduler.

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.kernel.org/pub/linux/utils/util-linux/.

util-linux			   July 2011			     IONICE(1)
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