Manpages - chrt.1

chrt - manipulate the real-time attributes of a process

chrt [options] priority command argument …

chrt [options] -p [/priority/] PID

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

-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.

-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.

-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.

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.

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

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.

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

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

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

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/>.