#Bash 的 chrt 命令
chrt [OPTION] -p [PRIORITY] PID
chrt [OPTION] PRIORITY [COMMAND] [ARGS ...]
功能
查看或设置进程的调度策略和优先级；或以指定的进程优先级执行命令。
类型
可执行文件（/usr/bin/chrt），属于 util-linux。
参数
OPTION选项：-a,--all-tasks- 设置检索进程下的所有任务（线程）-m,--max- 查看优先级的取值范围-p,--pid- 查看或设置的进程ID-v,--verbose- 显示状态信息--help- 显示帮助--version- 显示版本- 策略选项：
-o,--other- 将调度策略设为SCHED_OTHER（分时调度）；这是 Linux 的默认调度策略-f,--fifo- 将调度策略设为SCHED_FIFO（先进先出调度）；无时间片，可能饿死所有任务-r,--rr- 将调度策略设为SCHED_RR（轮流调度）；有时间片，可能饿死低优先级任务；不指定策略时默认使用此选项-b,--batch- 将调度策略设为SCHED_BATCH（批处理调度）-i,--idle- 将调度策略设为SCHED_IDLE（闲时调度）；用于低优先级任务-d,--deadline- 将调度策略设为SCHED_DEADLINE（截止时间调度）；在截止时间前完成的硬实时调度策略
- 调度选项：
-T,--sched-runtime nanoseconds- 指定SCHED_DEADLINE策略的运行时参数-P,--sched-period nanoseconds- 指定SCHED_DEADLINE策略的周期参数-D,--sched-deadline nanoseconds- 指定SCHED_DEADLINE策略的截止时间参数-R,--reset-on-fork- 使用SCHED_RESET_ON_FORK或SCHED_FLAG_RESET_ON_FORK标志
PRIORITY- 优先级；数值越大，优先级越高COMMAND- 要执行的命令ARGS- 命令的参数列表
#示例
查看优先级的取值范围
$ chrt -m
SCHED_OTHER min/max priority : 0/0
SCHED_FIFO min/max priority : 1/99
SCHED_RR min/max priority : 1/99
SCHED_BATCH min/max priority : 0/0
SCHED_IDLE min/max priority : 0/0
SCHED_DEADLINE min/max priority : 0/0
- 可以看到只有
SCHED_FIFO和SCHED_RR支持优先级
查看和设置进程调度策略和优先级
$ chrt -p $$ # 查看当前 bash 进程的调度策略和优先级
pid 944375's current scheduling policy: SCHED_OTHER
pid 944375's current scheduling priority: 0
$ sudo chrt -r -p 20 $$ # 将策略设为 SCHED_RR，优先级设为 20
$ chrt -p $$ # 再次查看当前 bash 进程的调度策略和优先级
pid 944375's current scheduling policy: SCHED_RR
pid 944375's current scheduling priority: 20
以指定的进程调度策略和优先级执行命令
$ chrt -i 0 tail -f /var/log/syslog # 以 SCHED_IDLE 策略执行 tail -f /var/log/syslog
- 虽然
SCHED_IDLE不支持优先级，但不能省略优先级参数，必须设置为0
#推荐阅读
#手册
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 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). 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.
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
Print 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 <[email protected]>, Karel Zak <[email protected]>
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 at
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 2.39.3 2023-11-21 CHRT(1)