.\" chrt(1) manpage
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.\" Copyright (C) 2004 Robert Love
.\" Copyright (C) 2015 Karel Zak <kzak@redhat.com>
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.TH CHRT 1 "January 2016" "util-linux" "User Commands"
.SH NAME
chrt \- manipulate the real-time attributes of a process
.SH SYNOPSIS
.B chrt
[options]
.IR priority\ command\  [ argument ...]
.br
.B chrt
[options]
.B \-p
.RI [ priority ]\  pid
.SH DESCRIPTION
.PP
.B chrt
sets or retrieves the real-time scheduling attributes of an existing \fIpid\fR,
or runs \fIcommand\fR with the given attributes.

.SH POLICIES
.TP
\fB\-o\fR, \fB\-\-other\fR
Set scheduling policy to
.BR SCHED_OTHER .
This is the default Linux scheduling policy.
.TP
\fB\-f\fR, \fB\-\-fifo\fR
Set scheduling policy to \fBSCHED_FIFO\fR.
.TP
\fB\-r\fR, \fB\-\-rr\fR
Set scheduling policy to
.BR SCHED_RR .
When no policy is defined, the
.B SCHED_RR
is used as the default.
.TP
\fB\-b\fR, \fB\-\-batch\fR
Set scheduling policy to
.B SCHED_BATCH
(Linux-specific, supported since 2.6.16).  The priority argument has to be set to zero.
.TP
\fB\-i\fR, \fB\-\-idle\fR
Set scheduling policy to
.B SCHED_IDLE
(Linux-specific, supported since 2.6.23).  The priority argument has to be set to zero.
.TP
.BR -d ,\  --deadline
Set scheduling policy to
.B SCHED_DEADLINE
(Linux-specific, supported since 3.14).  The priority argument has to be set to zero.
See also \fB\-\-sched\-runtime\fR, \fB\-\-sched\-deadline\fR and
\fB\-\-sched\-period\fR.  The relation between the options required by the kernel is
runtime <= deadline <= period.
.B chrt
copies \fIperiod\fR to \fIdeadline\fR if \fB\-\-sched\-deadline\fR is not specified and
\fIdeadline\fR to \fIruntime\fR if \fB\-\-sched\-runtime\fR is not specified.
It means that at least \fB\-\-sched\-period\fR has to be specified.  See
.BR sched (7)
for more details.

.SH "SCHEDULING OPTIONS"
.TP
\fB\-T\fR, \fB\-\-sched\-runtime\fR \fInanoseconds\fR
Specifies runtime parameter for SCHED_DEADLINE policy (Linux-specific).
.TP
\fB\-P\fR, \fB\-\-sched\-period\fR \fInanoseconds\fR
Specifies period parameter for SCHED_DEADLINE policy (Linux-specific).
.TP
\fB\-D\fR, \fB\-\-sched\-deadline\fR \fInanoseconds\fR
Specifies deadline parameter for SCHED_DEADLINE policy (Linux-specific).
.TP
\fB\-R\fR, \fB\-\-reset-on-fork\fR
Add
.B SCHED_RESET_ON_FORK
flag to the
.B SCHED_FIFO
or
.B SCHED_RR
scheduling policy (Linux-specific, supported since 2.6.31).

.SH OPTIONS
.TP
.BR -a ,\  --all-tasks
Set or retrieve the scheduling attributes of all the tasks (threads) for a
given PID.
.TP
.BR -m ,\  --max
Show minimum and maximum valid priorities, then exit.
.TP
.BR -p ,\  --pid
Operate on an existing PID and do not launch a new task.
.TP
.BR -v ,\  --verbose
Show status information.
.TP
.BR -V ,\  --version
Display version information and exit.
.TP
.BR -h ,\  --help
Display help text and exit.
.SH USAGE
.TP
The default behavior is to run a new command:
.B chrt
.I priority
.IR command\  [ arguments ]
.TP
You can also retrieve the real-time attributes of an existing task:
.B chrt \-p
.I pid
.TP
Or set them:
.B chrt \-r \-p
.I priority pid
.SH PERMISSIONS
A user must possess
.B CAP_SYS_NICE
to change the scheduling attributes of a process.  Any user can retrieve the
scheduling information.

.SH NOTES
Only
.BR SCHED_FIFO ,
.B SCHED_OTHER
and
.B SCHED_RR
are part of POSIX 1003.1b Process Scheduling.  The other scheduling attributes
may be ignored on some systems.
.P
Linux' default scheduling policy is
.BR SCHED_OTHER .
.SH SEE ALSO
.BR nice (1),
.BR renice (1),
.BR taskset (1),
.BR sched (7)
.sp
See
.BR sched_setscheduler (2)
for a description of the Linux scheduling scheme.
.SH AUTHORS
.UR rml@tech9.net
Robert Love
.UE
.br
.UR kzak@redhat.com
Karel Zak
.UE
.SH AVAILABILITY
The chrt command is part of the util-linux package and is available from
https://www.kernel.org/pub/linux/utils/util-linux/.