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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 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 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.

       -c class
              The scheduling class name or number. 0 for none, 1 for realtime, 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, ion-
              ice 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.

       # 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 scheduler.

       Jens Axboe <>

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

ionice                            August 2005                        ionice(1)