ionice

IONICE(1)                        User Commands                       IONICE(1)

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

SYNOPSIS
       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...]

DESCRIPTION
       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 ar-
       guments.  If no class is specified, then command will be executed  with
       the "best-effort" scheduling class.  The default priority level is 4.

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

       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  ac-
              tivity  should  be  zero.  This scheduling class does not take a
              priority argument.  Presently, this scheduling class is  permit-
              ted 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 I/O priority.  This class takes a  pri-
              ority argument from 0-7, with a lower number being higher prior-
              ity.  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 schedul-
              ing class.  The I/O priority is derived from the CPU nice  level
              of the process (same as before kernel 2.6.26).

       Realtime
              The  RT  scheduling class is given first access to the disk, re-
              gardless 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 re-
              ceive on each scheduling window.  This scheduling class  is  not
              permitted for an ordinary (i.e., non-root) user.

OPTIONS
       -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 high-
              est 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 insuffi-
              cient 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.

EXAMPLES
       # 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.

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

AUTHORS
       Jens Axboe <jens@axboe.dk>
       Karel Zak <kzak@redhat.com>

SEE ALSO
       ioprio_set(2)

AVAILABILITY
       The ionice command is part of the util-linux package and  is  available
       from https://www.kernel.org/pub/linux/utils/util-linux/.

util-linux                         July 2011                         IONICE(1)