chrt(1) — Linux manual page

CHRT(1)                       User Commands                      CHRT(1)

NAME

       chrt - manipulate the real-time attributes of a process

SYNOPSIS

       chrt [options] priority command argument ...

       chrt [options] -p [priority] PID

DESCRIPTION

       chrt sets or retrieves the real-time scheduling attributes of an
       existing PID, or runs command with the given attributes.

POLICIES

       -o, --other
           Set scheduling policy to SCHED_OTHER (time-sharing
           scheduling). This is the default Linux scheduling policy.

       -f, --fifo
           Set scheduling policy to SCHED_FIFO (first in-first out).

       -r, --rr
           Set scheduling policy to SCHED_RR (round-robin scheduling).
           When no policy is defined, the SCHED_RR is used as the
           default.

       -b, --batch
           Set scheduling policy to SCHED_BATCH (scheduling batch
           processes). Linux-specific, supported since 2.6.16. The
           priority argument has to be set to zero.

       -i, --idle
           Set scheduling policy to SCHED_IDLE (scheduling very low
           priority jobs). Linux-specific, supported since 2.6.23. The
           priority argument has to be set to zero.

       -d, --deadline
           Set scheduling policy to SCHED_DEADLINE (sporadic task model
           deadline scheduling). Linux-specific, supported since 3.14.
           The priority argument has to be set to zero. See also
           --sched-runtime, --sched-deadline and --sched-period. The
           relation between the options required by the kernel is
           runtime ⇐ deadline ⇐ period. chrt copies period to deadline
           if --sched-deadline is not specified and deadline to runtime
           if --sched-runtime is not specified. It means that at least
           --sched-period has to be specified. See sched(7) for more
           details.

SCHEDULING OPTIONS

       -T, --sched-runtime nanoseconds
           Specifies runtime parameter for SCHED_DEADLINE policy
           (Linux-specific).

       -P, --sched-period nanoseconds
           Specifies period parameter for SCHED_DEADLINE policy
           (Linux-specific). Note that the kernel’s lower limit is 100
           milliseconds.

       -D, --sched-deadline nanoseconds
           Specifies deadline parameter for SCHED_DEADLINE policy
           (Linux-specific).

       -R, --reset-on-fork
           Use SCHED_RESET_ON_FORK or SCHED_FLAG_RESET_ON_FORK flag.
           Linux-specific, supported since 2.6.31.

           Each thread has a reset-on-fork scheduling flag. When this
           flag is set, children created by fork(2) do not inherit
           privileged scheduling policies. After the reset-on-fork flag
           has been enabled, it can be reset only if the thread has the
           CAP_SYS_NICE capability. This flag is disabled in child
           processes created by fork(2).

           More precisely, if the reset-on-fork flag is set, the
           following rules apply for subsequently created children:

           •   If the calling thread has a scheduling policy of
               SCHED_FIFO or SCHED_RR, the policy is reset to
               SCHED_OTHER in child processes.

           •   If the calling process has a negative nice value, the
               nice value is reset to zero in child processes.

OPTIONS

       -a, --all-tasks
           Set or retrieve the scheduling attributes of all the tasks
           (threads) for a given PID.

       -m, --max
           Show minimum and maximum valid priorities, then exit.

       -p, --pid
           Operate on an existing PID and do not launch a new task.

       -v, --verbose
           Show status information.

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

       -V, --version
           Print version and exit.

EXAMPLES

       The default behavior is to run a new command:

          chrt priority command [arguments]

       You can also retrieve the real-time attributes of an existing
       task:

          chrt -p PID

       Or set them:

          chrt -r -p priority PID

       This, for example, sets real-time scheduling to priority 30 for
       the process PID with the SCHED_RR (round-robin) class:

          chrt -r -p 30 PID

       Reset priorities to default for a process:

          chrt -o -p 0 PID

       See sched(7) for a detailed discussion of the different scheduler
       classes and how they interact.

PERMISSIONS

       A user must possess CAP_SYS_NICE to change the scheduling
       attributes of a process. Any user can retrieve the scheduling
       information.

NOTES

       Only SCHED_FIFO, SCHED_OTHER and SCHED_RR are part of POSIX
       1003.1b Process Scheduling. The other scheduling attributes may
       be ignored on some systems.

       Linux' default scheduling policy is SCHED_OTHER.

AUTHORS

       Robert Love <rml@tech9.net>, Karel Zak <kzak@redhat.com>

SEE ALSO

       nice(1), renice(1), taskset(1), sched(7)

       See sched_setscheduler(2) for a description of the Linux
       scheduling scheme.

REPORTING BUGS

       For bug reports, use the issue tracker at
       https://github.com/util-linux/util-linux/issues.

AVAILABILITY

       The chrt command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>. This page
       is part of the util-linux (a random collection of Linux
       utilities) project. Information about the project can be found at
       ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have
       a bug report for this manual page, send it to
       util-linux@vger.kernel.org. This page was obtained from the
       project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2024-06-14. (At that time, the date of the most recent commit
       that was found in the repository was 2024-06-10.) If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page,
       or you have corrections or improvements to the information in
       this COLOPHON (which is not part of the original manual page),
       send a mail to man-pages@man7.org

util-linux 2.39.594-1e0ad      2023-08-25                        CHRT(1)

Pages that refer to this page: coresched(1), renice(1), taskset(1), sched_setattr(2), sched_setscheduler(2), sched(7)

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