Manual: chrt

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 and custom slice length for SCHED_OTHER and SCHED_BATCH policies
	   (Linux-specific). Note that custom slice length via the runtime parameter is supported since Linux 6.12.

       -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
	   Display 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 , Karel Zak 

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 .

AVAILABILITY
       The chrt command is part of the util-linux package which can be downloaded from Linux Kernel Archive
       .

util-linux 2.41.3					 2025-12-15						     CHRT(1)