chrt

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).

       -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:

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

       o   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.

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

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

USAGE
       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

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/karelzak/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/>.

util-linux 2.37.2                 2021-06-02                           CHRT(1)