.\" chrt(1) manpage
.\"
.\" Copyright (C) 2004 Robert Love
.\"
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
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.\" 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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.\" License along with this manual; if not, write to the Free
.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
.\" USA.
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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
(the 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 usage information 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 \-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.
.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/.