chrt (1) - Linux Manuals
chrt: manipulate the real-time attributes of a process
chrt - manipulate the real-time attributes of a process
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.
- Set scheduling policy to SCHED_OTHER (time-sharing scheduling). This is the default Linux scheduling policy.
- Set scheduling policy to SCHED_FIFO (first in-first out).
- Set scheduling policy to SCHED_RR (round-robin scheduling). When no policy is defined, the SCHED_RR is used as the default.
- 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.
- 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.
- 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.
-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).
- 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.
- Set or retrieve the scheduling attributes of all the tasks (threads) for a given PID.
- Show minimum and maximum valid priorities, then exit.
- Operate on an existing PID and do not launch a new task.
- Show status information.
- Display version information and exit.
- 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.
For bug reports, use the issue tracker at <https://github.com/karelzak/util-linux/issues>.
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/>.
nice(1), renice(1), taskset(1), sched(7)
See sched_setscheduler(2) for a description of the Linux scheduling scheme.