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           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
           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  pro-
                  cess (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. 0 for none, 1 for real time, 2 for best-
                  effort, 3 for idle.


           # 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  avail-
           able from

    ionice August 2005 ionice(1)


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