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Name

chrt - manipulate the real-time attributes of a process

Synopsis

chrt [options] prio command [arg]...
chrt [options] -p [prio] pid

Description

chrt sets or retrieves the real-time scheduling attributes of an existing pid, or runs command with the given attributes. Both policy (one of SCHED_OTHER, SCHED_FIFO, SCHED_RR, SCHED_BATCH, or SCHED_IDLE) and 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.

Options

-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).
-f, --fifo
Set scheduling policy to SCHED_FIFO.
-i, --idle
Set scheduling policy to SCHED_IDLE (Linux specific).
-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, --rr
Set scheduling policy to SCHED_RR. When policy is not defined the SCHED_RR is used as default.
-R, --reset-on-fork
Add SCHED_RESET_ON_FORK flag to the SCHED_FIFO or SCHED_RR scheduling policy (Linux specific).
-v, --verbose
Show status information.
-h, --help
Display help text and exit.
-V, --version
Display version information and exit.

Usage

The default behavior is to run a new command:
chrt prio command [arguments]
You can also retrieve the real-time attributes of an existing task:
chrt -p pid
Or set them:
chrt -r -p prio 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.

Author

Written by Robert M. Love.

Copyright

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.

See Also

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

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

Availability

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

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