chrt

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. Both the policy (one of SCHED_OTHER, SCHED_FIFO, SCHED_RR, SCHED_BATCH, or SCHED_IDLE) and the priority can be set and retrieved.

The SCHED_BATCH policy is supported since Linux 2.6.16. The SCHED_IDLE policy is supported since Linux 2.6.23.

The SCHED_RESET_ON_FORK flag for policies SCHED_RR and SCHED_FIFO is supported since Linux 2.6.31.

-a, --all-tasks

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

-b, --batch

Set scheduling policy to SCHED_BATCH (Linux-specific). The priority argument has to be set to zero.

-f, --fifo

Set scheduling policy to SCHED_FIFO.

-i, --idle

Set scheduling policy to SCHED_IDLE (Linux-specific). The priority argument has to be set to zero.

-m, --max

Show minimum and maximum valid priorities, then exit.

-o, --other

Set policy scheduling policy to SCHED_OTHER.

-p, --pid

Operate on an existing PID and do not launch a new task.

-R, --reset-on-fork

Add SCHED_RESET_ON_FORK flag to the SCHED_FIFO or SCHED_RR scheduling policy (Linux-specific).

-r, --rr

Set scheduling policy to SCHED_RR. When policy is not defined the SCHED_RR is used as default.

-v, --verbose

Show status information.

-V, --version

Display version information and exit.

-h, --help

Display help text 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

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.

taskset(1), nice(1), renice(1)

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

Written by Robert M. Love.

Copyright © 2004 Robert M. Love. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The chrt command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.