chrt (1) Linux Manual Page
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.
-V, –version
- Display version information and exit.
-h, –help
- Display help text 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
See Also
nice(1), renice(1), taskset(1), sched(7) See sched_setscheduler(2) for a description of the Linux scheduling scheme.