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Linux 2.6 - man page for ionice (linux section 1)

ionice(1)										ionice(1)

       ionice - get/set program io scheduling class and priority

       ionice [[-c class] [-n classdata] [-t]] -p PID [PID]...
       ionice [-c class] [-n classdata] [-t] COMMAND [ARG]...

       This program sets or gets the io scheduling class and priority for a program.  If no argu-
       ments 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 pro-
	      gram has asked for disk io for a defined grace period. The impact of idle  io  pro-
	      cesses  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 for-
	      mally  uses  "none"  as scheduling class, but the io scheduler will treat such pro-
	      cesses 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_prior-
	      ity = (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 schedul-
	      ing window. This scheduling class is not permitted for an ordinary (i.e., non-root)

       -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  argu-
	      ment 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  hap-
	      pen due to insufficient privileges or old kernel version.

       # 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.

       Linux  supports	io  scheduling priorities and classes since 2.6.13 with the CFQ io sched-

       Jens Axboe <jens@axboe.dk>

       The ionice command is part of the util-linux package and is available from  ftp://ftp.ker-

ionice					   August 2005					ionice(1)

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