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 (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 argu- ment 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 and custom slice length for SCHED_OTHER and SCHED_BATCH policies (Linux-specific). Note that custom slice length via the runtime parameter is supported since Linux 6.12. -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-spe- cific). -R, --reset-on-fork Use SCHED_RESET_ON_FORK or SCHED_FLAG_RESET_ON_FORK flag. Linux-spe- cific, 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 poli- cies. 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 dis- abled 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 Display 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@tech9.net>, Karel Zak <kzak@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 <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/>. util-linux 2.41.2 2025-09-22 CHRT(1)
NAME | SYNOPSIS | DESCRIPTION | POLICIES | SCHEDULING OPTIONS | OPTIONS | EXAMPLES | PERMISSIONS | NOTES | AUTHORS | SEE ALSO | REPORTING BUGS | AVAILABILITY
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