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/>.