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.
−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.
−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.
−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.
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.
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.
Robert Love <[email protected]>, Karel Zak <[email protected]>
nice(1), renice(1), taskset(1), sched(7)
See sched_setscheduler(2) for a description of the Linux scheduling scheme.
For bug reports, use the issue tracker at <https://github.com/util−linux/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/>.