ionice(1)						      General Commands Manual							 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 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 dynam-
	      ically 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 processes. If this argument is not given, ionice will run the listed pro-
	      gram 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 privileges 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 package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

ionice								    August 2005 							 ionice(1)