'\" t
.\"     Title: chrt
.\"    Author: [see the "AUTHOR(S)" section]
.\" Generator: Asciidoctor 2.0.20
.\"      Date: 2025-02-26
.\"    Manual: User Commands
.\"    Source: util-linux 2.41
.\"  Language: English
.\"
.TH "CHRT" "1" "2025-02-26" "util\-linux 2.41" "User Commands"
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.ss \n[.ss] 0
.nh
.ad l
.de URL
\fI\\$2\fP <\\$1>\\$3
..
.als MTO URL
.if \n[.g] \{\
.  mso www.tmac
.  am URL
.    ad l
.  .
.  am MTO
.    ad l
.  .
.  LINKSTYLE blue R < >
.\}
.SH "NAME"
chrt \- manipulate the real\-time attributes of a process
.SH "SYNOPSIS"
.sp
\fBchrt\fP [options] \fIpriority command argument\fP ...
.sp
\fBchrt\fP [options] \fB\-p\fP [\fIpriority\fP] \fIPID\fP
.SH "DESCRIPTION"
.sp
\fBchrt\fP sets or retrieves the real\-time scheduling attributes of an existing \fIPID\fP, or runs \fIcommand\fP with the given attributes.
.SH "POLICIES"
.sp
\fB\-o\fP, \fB\-\-other\fP
.RS 4
Set scheduling policy to \fBSCHED_OTHER\fP (time\-sharing scheduling). This is the default Linux scheduling policy.
.RE
.sp
\fB\-f\fP, \fB\-\-fifo\fP
.RS 4
Set scheduling policy to \fBSCHED_FIFO\fP (first in\-first out).
.RE
.sp
\fB\-r\fP, \fB\-\-rr\fP
.RS 4
Set scheduling policy to \fBSCHED_RR\fP (round\-robin scheduling). When no policy is defined, the \fBSCHED_RR\fP is used as the default.
.RE
.sp
\fB\-b\fP, \fB\-\-batch\fP
.RS 4
Set scheduling policy to \fBSCHED_BATCH\fP (scheduling batch processes). Linux\-specific, supported since 2.6.16. The priority argument has to be set to zero.
.RE
.sp
\fB\-i\fP, \fB\-\-idle\fP
.RS 4
Set scheduling policy to \fBSCHED_IDLE\fP (scheduling very low priority jobs). Linux\-specific, supported since 2.6.23. The priority argument has to be set to zero.
.RE
.sp
\fB\-d\fP, \fB\-\-deadline\fP
.RS 4
Set scheduling policy to \fBSCHED_DEADLINE\fP (sporadic task model deadline scheduling). Linux\-specific, supported since 3.14. The priority argument has to be set to zero. See also \fB\-\-sched\-runtime\fP, \fB\-\-sched\-deadline\fP and \fB\-\-sched\-period\fP. The relation between the options required by the kernel is runtime \(lA deadline \(lA period. \fBchrt\fP copies \fIperiod\fP to \fIdeadline\fP if \fB\-\-sched\-deadline\fP is not specified and \fIdeadline\fP to \fIruntime\fP if \fB\-\-sched\-runtime\fP is not specified. It means that at least \fB\-\-sched\-period\fP has to be specified. See \fBsched\fP(7) for more details.
.RE
.SH "SCHEDULING OPTIONS"
.sp
\fB\-T\fP, \fB\-\-sched\-runtime\fP \fInanoseconds\fP
.RS 4
Specifies runtime parameter for \fBSCHED_DEADLINE\fP and custom slice length for \fBSCHED_OTHER\fP and \fBSCHED_BATCH\fP policies (Linux\-specific). Note that custom slice length via the runtime parameter is supported since Linux 6.12.
.RE
.sp
\fB\-P\fP, \fB\-\-sched\-period\fP \fInanoseconds\fP
.RS 4
Specifies period parameter for \fBSCHED_DEADLINE\fP policy (Linux\-specific). Note that the kernel\(cqs lower limit is 100 milliseconds.
.RE
.sp
\fB\-D\fP, \fB\-\-sched\-deadline\fP \fInanoseconds\fP
.RS 4
Specifies deadline parameter for \fBSCHED_DEADLINE\fP policy (Linux\-specific).
.RE
.sp
\fB\-R\fP, \fB\-\-reset\-on\-fork\fP
.RS 4
Use \fBSCHED_RESET_ON_FORK\fP or \fBSCHED_FLAG_RESET_ON_FORK\fP flag. Linux\-specific, supported since 2.6.31.
.sp
Each thread has a \fIreset\-on\-fork\fP scheduling flag. When this flag is set, children created by \fBfork\fP(2) do not inherit privileged scheduling policies. After the \fIreset\-on\-fork\fP flag has been enabled, it can be reset only if the thread has the \fBCAP_SYS_NICE\fP capability. This flag is disabled in child processes created by \fBfork\fP(2).
.sp
More precisely, if the \fIreset\-on\-fork\fP flag is set, the following rules apply for subsequently created children:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.  sp -1
.  IP \(bu 2.3
.\}
If the calling thread has a scheduling policy of \fBSCHED_FIFO\fP or \fBSCHED_RR\fP, the policy is reset to \fBSCHED_OTHER\fP in child processes.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.  sp -1
.  IP \(bu 2.3
.\}
If the calling process has a negative nice value, the nice value is reset to zero in child processes.
.RE
.RE
.SH "OPTIONS"
.sp
\fB\-a\fP, \fB\-\-all\-tasks\fP
.RS 4
Set or retrieve the scheduling attributes of all the tasks (threads) for a given PID.
.RE
.sp
\fB\-m\fP, \fB\-\-max\fP
.RS 4
Show minimum and maximum valid priorities, then exit.
.RE
.sp
\fB\-p\fP, \fB\-\-pid\fP
.RS 4
Operate on an existing PID and do not launch a new task.
.RE
.sp
\fB\-v\fP, \fB\-\-verbose\fP
.RS 4
Show status information.
.RE
.sp
\fB\-h\fP, \fB\-\-help\fP
.RS 4
Display help text and exit.
.RE
.sp
\fB\-V\fP, \fB\-\-version\fP
.RS 4
Display version and exit.
.RE
.SH "EXAMPLES"
.sp
The default behavior is to run a new command:
.RS 4
.RE
.RS 3
.ll -.6i
.sp
\fBchrt\fP \fIpriority\fP \fIcommand\fP [\fIarguments\fP]
.br
.RE
.ll
.sp
You can also retrieve the real\-time attributes of an existing task:
.RS 4
.RE
.RS 3
.ll -.6i
.sp
\fBchrt \-p\fP \fIPID\fP
.br
.RE
.ll
.sp
Or set them:
.RS 4
.RE
.RS 3
.ll -.6i
.sp
\fBchrt \-r \-p\fP \fIpriority PID\fP
.br
.RE
.ll
.sp
This, for example, sets real\-time scheduling to priority \fI30\fP for the process \fIPID\fP with the \fBSCHED_RR\fP (round\-robin) class:
.RS 4
.RE
.RS 3
.ll -.6i
.sp
\fBchrt \-r \-p 30\fP \fIPID\fP
.br
.RE
.ll
.sp
Reset priorities to default for a process:
.RS 4
.RE
.RS 3
.ll -.6i
.sp
\fBchrt \-o \-p 0\fP \fIPID\fP
.br
.RE
.ll
.sp
See \fBsched\fP(7) for a detailed discussion of the different scheduler classes and how they interact.
.SH "PERMISSIONS"
.sp
A user must possess \fBCAP_SYS_NICE\fP to change the scheduling attributes of a process. Any user can retrieve the scheduling information.
.SH "NOTES"
.sp
Only \fBSCHED_FIFO\fP, \fBSCHED_OTHER\fP and \fBSCHED_RR\fP are part of POSIX 1003.1b Process Scheduling. The other scheduling attributes may be ignored on some systems.
.sp
Linux\*(Aq default scheduling policy is \fBSCHED_OTHER\fP.
.SH "AUTHORS"
.sp
.MTO "rml\(attech9.net" "Robert Love" ","
.MTO "kzak\(atredhat.com" "Karel Zak" ""
.SH "SEE ALSO"
.sp
\fBnice\fP(1),
\fBrenice\fP(1),
\fBtaskset\fP(1),
\fBsched\fP(7)
.sp
See \fBsched_setscheduler\fP(2) for a description of the Linux scheduling scheme.
.SH "REPORTING BUGS"
.sp
For bug reports, use the \c
.URL "https://github.com/util\-linux/util\-linux/issues" "issue tracker" "."
.SH "AVAILABILITY"
.sp
The \fBchrt\fP command is part of the util\-linux package which can be downloaded from \c
.URL "https://www.kernel.org/pub/linux/utils/util\-linux/" "Linux Kernel Archive" "."