.\" 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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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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.\" 2002-05-11 Robert Love <rml@tech9.net>
.\" 	Initial version
.\"
.TH CHRT "1" "Apr 2003" "schedutils" "Linux User's Manual"
.SH NAME
chrt \- manipulate 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
.BR chrt (1)
sets or retrieves the real-time scheduling attributes of an existing PID or
runs COMMAND 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.
.SH OPTIONS
.TP
.B -p, --pid
operate on an existing PID and do not launch a new task
.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 schedulng 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 -r, --rr
set scheduling policy to
.BR SCHED_RR
(the default)
.TP
.B -h, --help
display usage information and exit
.TP
.B -v, --version
output version information and exit
.SH USAGE
.TP
The default behavior is to run a new command::
chrt prio command [arguments]
.TP
You can also retrieve the real-time attributes of an existing task:
chrt -p pid
.TP
Or set them:
chrt -p 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-ng package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.