Provided by: util-linux_2.34-0.1ubuntu9.6_amd64 bug

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 arguments.  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
              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  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).

       Realtime
              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.

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 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.

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/.