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). 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
Print 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 <rml [AT] tech9.net>, Karel Zak <kzak [AT] 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/>;.