table of contents
| 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. This is the default Linux scheduling policy.
- -f, --fifo
- Set scheduling policy to SCHED_FIFO.
- -r, --rr
- Set scheduling policy to SCHED_RR. When no policy is defined, the SCHED_RR is used as the default.
- -b, --batch
- Set scheduling policy to SCHED_BATCH (Linux-specific, supported since 2.6.16). The priority argument has to be set to zero.
- -i, --idle
- Set scheduling policy to SCHED_IDLE (Linux-specific, supported since 2.6.23). The priority argument has to be set to zero.
- -d, --deadline
- Set scheduling policy to SCHED_DEADLINE (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.
SEE ALSO¶
nice(1), renice(1), taskset(1), sched(7)
See sched_setscheduler(2) for a description of the Linux scheduling scheme.
AUTHORS¶
AVAILABILITY¶
The chrt command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.
| January 2016 | util-linux |