ionice - set or get process I/O scheduling class and priority


   ionice [-c class] [-n level] [-t] -p PID...
   ionice [-c class] [-n level] [-t] -P PGID...
   ionice [-c class] [-n level] [-t] -u UID...
   ionice [-c class] [-n level] [-t] command [argument...]


   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

   As of this writing, a  process  can  be  in  one  of  three  scheduling

   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
          permitted for an ordinary user (since kernel 2.6.25).

          This is the effective scheduling class for any process that  has
          not  asked  for  a  specific  I/O  priority.  This class takes a
          priority argument from 0-7, with a  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  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
          scheduling class.  The I/O priority is derived from the CPU nice
          level of the process (same as before kernel 2.6.26).

          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 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),  and 0 represents the
          highest priority level.

   -p, --pid PID...
          Specify the process IDs of running processes for which to get or
          set the scheduling parameters.

   -P, --pgid PGID...
          Specify  the process group 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
          insufficient privileges or an old kernel version.

   -h, --help
          Display help text and exit.

   -u, --uid UID...
          Specify  the  user  IDs of running processes for which to get or
          set the scheduling parameters.

   -V, --version
          Display version information and exit.


   # 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.


   Linux supports I/O scheduling priorities and classes since 2.6.13  with
   the CFQ I/O scheduler.


   Jens Axboe <>
   Karel Zak <>


   The  ionice  command is part of the util-linux package and is available


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