.\" chrt(1) manpage
.\"
.\" Copyright (C) 2004 Robert Love
.\"
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.\" modify it under the terms of the GNU General Public License as
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.\" This manual is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\" GNU General Public License for more details.
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.\" 2002-05-11 Robert Love <rml@tech9.net>
.\" 	Initial version
.\"
.TH CHRT 1 "June 2010" "util-linux" "User Commands"
.SH NAME
chrt \- manipulate the real-time attributes of a process
.SH SYNOPSIS
.B chrt
.RI [ options ]\  prio
.IR command\  [ arg ]...
.br
.B chrt
.RI [ options ]
.B \-p
.RI [ prio ]\  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 policy (one of
.BR SCHED_OTHER ,
.BR SCHED_FIFO ,
.BR SCHED_RR ,
.BR SCHED_BATCH ,
or
.BR SCHED_IDLE )
and 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.
.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
.B -a, --all-tasks
Set or retrieve the scheduling attributes of all the tasks (threads) for a
given PID.
.TP
.B -b, --batch
Set scheduling policy to
.BR SCHED_BATCH
(Linux specific).
.TP
.B -f, --fifo
Set scheduling policy to
.BR SCHED_FIFO .
.TP
.B -i, --idle
Set scheduling policy to
.BR SCHED_IDLE
(Linux specific).
.TP
.B -m, --max
Show minimum and maximum valid priorities, then exit.
.TP
.B -o, --other
Set policy scheduling policy to
.BR SCHED_OTHER .
.TP
.B -p, --pid
Operate on an existing PID and do not launch a new task.
.TP
.B -r, --rr
Set scheduling policy to
.BR SCHED_RR .
When policy is not defined the
.B SCHED_RR
is used as default.
.TP
.B -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
.B -v, --verbose
Show status information.
.TP
.B -h, --help
Display help text and exit.
.TP
.B -V, --version
Display version information and exit.
.SH USAGE
.TP
The default behavior is to run a new command:
.B chrt
.I prio
.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 prio 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 AUTHOR
Written by Robert M. Love.
.SH COPYRIGHT
Copyright \(co 2004 Robert M. Love
.br
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 "SEE ALSO"
.BR taskset (1),
.BR nice (1),
.BR renice (1)
.sp
See
.BR sched_setscheduler (2)
for a description of the Linux scheduling scheme.
.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/.