.\" chrt(1) manpage
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.\" Copyright (C) 2004 Robert Love
.\"
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.TH CHRT 1 "August 2014" "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.  Both the policy (one of
.BR SCHED_OTHER ,
.BR SCHED_FIFO ,
.BR SCHED_RR ,
.BR SCHED_BATCH ,
.BR SCHED_DEADLINE ,
or
.BR SCHED_IDLE )
and the priority can be set and retrieved.
.PP
The
.BR SCHED_BATCH
policy is supported since Linux 2.6.16.  The
.BR SCHED_IDLE
policy is supported since Linux 2.6.23.  The
.BR SCHED_DEADLINE
policy is supported since Linux 3.14.
.PP
The
.BR SCHED_RESET_ON_FORK
flag for policies SCHED_RR and SCHED_FIFO is supported
since Linux 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 -b ,\  --batch
Set scheduling policy to
.B SCHED_BATCH
(Linux-specific). The priority argument has to be set to zero.
.TP
.BR -d ,\  --deadline
Set policy scheduling policy to
.BR SCHED_DEADLINE
(Linux-specific). 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 kernel is runtime <= deadline <= period.
.B chrt
copies \fIperiod\fR to \fIdeadline\fR if \fB\-\-sched\-deadline\fR is no specified and
\fIdeadline\fR to \fIruntime\fR if \fB\-\-sched\-runtime\fR is no specified. It means at least
\fB\-\-sched\-period\fR has to be specified. See
.BR sched (7)
for more details.
.TP
.BR -f ,\  --fifo
Set scheduling policy to
.BR SCHED_FIFO .
.TP
.BR -i ,\  --idle
Set scheduling policy to
.B SCHED_IDLE
(Linux-specific). The priority argument has to be set to zero.
.TP
.BR -m ,\  --max
Show minimum and maximum valid priorities, then exit.
.TP
.BR -o ,\  --other
Set policy scheduling policy to
.BR SCHED_OTHER .
.TP
.BR -p ,\  --pid
Operate on an existing PID and do not launch a new task.
.TP
.BR -R ,\  --reset-on-fork
Add
.B SCHED_RESET_ON_FORK
flag to the
.B SCHED_FIFO
or
.B SCHED_RR
scheduling policy (Linux-specific).
.TP
.BR -r ,\  --rr
Set scheduling policy to
.BR SCHED_RR .
When policy is not defined the
.B SCHED_RR
is used as default.
.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
.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
.BR CAP_SYS_NICE
to change the scheduling attributes of a process.  Any user can retrieve the
scheduling information.
.SH NOTES
Only
.BR SCHED_FIFO ,
.BR SCHED_OTHER
and
.BR 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 taskset (1),
.BR nice (1),
.BR renice (1)
.BR sched (7)
.sp
See
.BR sched_setscheduler (2)
for a description of the Linux scheduling scheme.
.SH AUTHOR
Written by Robert M. Love.
.SH COPYRIGHT
Copyright \(co 2004 Robert M. Love.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
.SH AVAILABILITY
The chrt command is part of the util-linux package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.