1CHRT(1)                          User Commands                         CHRT(1)
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3
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NAME

6       chrt - manipulate the real-time attributes of a process
7

SYNOPSIS

9       chrt [options] priority command argument ...
10
11       chrt [options] -p [priority] PID
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DESCRIPTION

14       chrt sets or retrieves the real-time scheduling attributes of an
15       existing PID, or runs command with the given attributes.
16

POLICIES

18       -o, --other
19           Set scheduling policy to SCHED_OTHER (time-sharing scheduling).
20           This is the default Linux scheduling policy.
21
22       -f, --fifo
23           Set scheduling policy to SCHED_FIFO (first in-first out).
24
25       -r, --rr
26           Set scheduling policy to SCHED_RR (round-robin scheduling). When no
27           policy is defined, the SCHED_RR is used as the default.
28
29       -b, --batch
30           Set scheduling policy to SCHED_BATCH (scheduling batch processes).
31           Linux-specific, supported since 2.6.16. The priority argument has
32           to be set to zero.
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34       -i, --idle
35           Set scheduling policy to SCHED_IDLE (scheduling very low priority
36           jobs). Linux-specific, supported since 2.6.23. The priority
37           argument has to be set to zero.
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39       -d, --deadline
40           Set scheduling policy to SCHED_DEADLINE (sporadic task model
41           deadline scheduling). Linux-specific, supported since 3.14. The
42           priority argument has to be set to zero. See also --sched-runtime,
43           --sched-deadline and --sched-period. The relation between the
44           options required by the kernel is runtime ⇐ deadline ⇐ period. chrt
45           copies period to deadline if --sched-deadline is not specified and
46           deadline to runtime if --sched-runtime is not specified. It means
47           that at least --sched-period has to be specified. See sched(7) for
48           more details.
49

SCHEDULING OPTIONS

51       -T, --sched-runtime nanoseconds
52           Specifies runtime parameter for SCHED_DEADLINE policy
53           (Linux-specific).
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55       -P, --sched-period nanoseconds
56           Specifies period parameter for SCHED_DEADLINE policy
57           (Linux-specific). Note that the kernel’s lower limit is 100
58           milliseconds.
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60       -D, --sched-deadline nanoseconds
61           Specifies deadline parameter for SCHED_DEADLINE policy
62           (Linux-specific).
63
64       -R, --reset-on-fork
65           Use SCHED_RESET_ON_FORK or SCHED_FLAG_RESET_ON_FORK flag.
66           Linux-specific, supported since 2.6.31.
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68           Each thread has a reset-on-fork scheduling flag. When this flag is
69           set, children created by fork(2) do not inherit privileged
70           scheduling policies. After the reset-on-fork flag has been enabled,
71           it can be reset only if the thread has the CAP_SYS_NICE capability.
72           This flag is disabled in child processes created by fork(2).
73
74           More precisely, if the reset-on-fork flag is set, the following
75           rules apply for subsequently created children:
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77           •   If the calling thread has a scheduling policy of SCHED_FIFO or
78               SCHED_RR, the policy is reset to SCHED_OTHER in child
79               processes.
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81           •   If the calling process has a negative nice value, the nice
82               value is reset to zero in child processes.
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OPTIONS

85       -a, --all-tasks
86           Set or retrieve the scheduling attributes of all the tasks
87           (threads) for a given PID.
88
89       -m, --max
90           Show minimum and maximum valid priorities, then exit.
91
92       -p, --pid
93           Operate on an existing PID and do not launch a new task.
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95       -v, --verbose
96           Show status information.
97
98       -h, --help
99           Display help text and exit.
100
101       -V, --version
102           Print version and exit.
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EXAMPLES

105       The default behavior is to run a new command:
106
107          chrt priority command [arguments]
108
109       You can also retrieve the real-time attributes of an existing task:
110
111          chrt -p PID
112
113       Or set them:
114
115          chrt -r -p priority PID
116
117       This, for example, sets real-time scheduling to priority 30 for the
118       process PID with the SCHED_RR (round-robin) class:
119
120          chrt -r -p 30 PID
121
122       Reset priorities to default for a process:
123
124          chrt -o -p 0 PID
125
126       See sched(7) for a detailed discussion of the different scheduler
127       classes and how they interact.
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PERMISSIONS

130       A user must possess CAP_SYS_NICE to change the scheduling attributes of
131       a process. Any user can retrieve the scheduling information.
132

NOTES

134       Only SCHED_FIFO, SCHED_OTHER and SCHED_RR are part of POSIX 1003.1b
135       Process Scheduling. The other scheduling attributes may be ignored on
136       some systems.
137
138       Linux' default scheduling policy is SCHED_OTHER.
139

AUTHORS

141       Robert Love <rml@tech9.net>, Karel Zak <kzak@redhat.com>
142

SEE ALSO

144       nice(1), renice(1), taskset(1), sched(7)
145
146       See sched_setscheduler(2) for a description of the Linux scheduling
147       scheme.
148

REPORTING BUGS

150       For bug reports, use the issue tracker at
151       https://github.com/util-linux/util-linux/issues.
152

AVAILABILITY

154       The chrt command is part of the util-linux package which can be
155       downloaded from Linux Kernel Archive
156       <https://www.kernel.org/pub/linux/utils/util-linux/>.
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160util-linux 2.39.2                 2023-08-17                           CHRT(1)