--- name: "chrt" section: "1" platform: "linux" package: "util-linux" version: "2.42.4-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/chrt" --- # chrt(1) manipulate the real-time attributes of a process ## NAME chrt - manipulate the real-time attributes of a process ## SYNOPSIS **chrt** \[options\] \[*priority*\] *command* \[*argument*...\] **chrt --pid** \[options\] \[*priority*\] *PID* ## DESCRIPTION **chrt** sets or retrieves the real-time scheduling attributes of an existing *PID*, or runs *command* with the given attributes. ## POLICY OPTIONS - **-o**, **--other** Set scheduling policy to **SCHED\_OTHER** (time-sharing scheduling). This is the default Linux scheduling policy. Since util-linux v2.42, the priority argument is optional; if specified, it must be set to zero. - **-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. Since util-linux v2.42, the priority argument is optional; if specified, it must be set to zero. - **-i**, **--idle** Set scheduling policy to **SCHED\_IDLE** (scheduling very low priority jobs). Linux-specific, supported since 2.6.23. Since util-linux v2.42, the priority argument is optional; if specified, it must be set to zero. - **-d**, **--deadline** Set scheduling policy to **SCHED\_DEADLINE** (sporadic task model deadline scheduling). Linux-specific, supported since 3.14. Since util-linux v2.42, the priority argument is optional; if specified, it must 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)](/sched/7.md) for more details. - **-e**, **--ext** Set scheduling policy to **SCHED\_EXT** (BPF program-defined scheduling). Linux-specific, supported since 6.12. Since util-linux v2.42, the priority argument is optional; if specified, it must be set to zero. Note that for the policy to be recognized, the following kernel configuration options need to be enabled: **CONFIG\_BPF**, **CONFIG\_SCHED\_CLASS\_EXT**, **CONFIG\_BPF\_SYSCALL**, **CONFIG\_BPF\_JIT**, **CONFIG\_DEBUG\_INFO\_BTF**, **CONFIG\_BPF\_JIT\_ALWAYS\_ON** and **CONFIG\_BPF\_JIT\_DEFAULT\_ON**. ## 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 microseconds. - **-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)](/fork/2.md) 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)](/fork/2.md). 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 --pid** *PID*\ Or set them: **chrt --pid** *policy-option priority PID*\ For example, to set the scheduling policy to **SCHED\_RR** (round-robin) and the priority to **30** for process **1234**: **chrt --pid -r 30 1234**\ Reset priorities to default for a process: **chrt --pid -o 0** *PID*\ Set a custom slice of 1 ms for a **SCHED\_OTHER** task (priority is optional for policies other than **SCHED\_FIFO** and **SCHED\_RR**): **chrt --pid -o -T 1000000** *PID*\ See [**sched**(7)](/sched/7.md) 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* \, *Karel Zak* \ ## SEE ALSO [**nice**(1)](/nice/1.md), [**renice**(1)](/renice/1.md), [**taskset**(1)](/taskset/1.md), [**sched**(7)](/sched/7.md) See [**sched\_setscheduler**(2)](/sched_setscheduler/2.md) for a description of the Linux scheduling scheme. ## REPORTING BUGS For bug reports, use the *issue tracker* \. ## AVAILABILITY The **chrt** command is part of the util-linux package which can be downloaded from *Linux Kernel Archive* \.