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:
• 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.
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/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/>.
util-linux 2.38.1 2022-05-11 CHRT(1)
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