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[thirdparty/util-linux.git] / schedutils / taskset.1

.\" taskset(1) manpage
.\"
.\" Copyright (C) 2004 Robert Love
.\"
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.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License.
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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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.\" You should have received a copy of the GNU General Public
.\" License along with this manual; if not, write to the Free
.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
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.\" 2002-05-11 Robert Love <rml@tech9.net>
.\" 	Initial version
.\"
.TH TASKSET "1" "Apr 2003" "schedutils" "Linux User's Manual"
.SH NAME
taskset \- retrieve or set a process's CPU affinity
.SH SYNOPSIS
.B taskset
.RI [ options ]\  mask
.IR command\  [ arg ]...
.br
.B taskset
.RI [ options ]
.B \-p
.RI [ mask ]\  pid
.SH DESCRIPTION
.PP
.BR taskset
is used to set or retrieve the CPU affinity of a running process given its PID
or to launch a new COMMAND with a given CPU affinity.  CPU affinity is a
scheduler property that "bonds" a process to a given set of CPUs on the system.
The Linux scheduler will honor the given CPU affinity and the process will not
run on any other CPUs.  Note that the Linux scheduler also supports natural
CPU affinity: the scheduler attempts to keep processes on the same CPU as long
as practical for performance reasons.  Therefore, forcing a specific CPU
affinity is useful only in certain applications.
.sp
The CPU affinity is represented as a bitmask, with the lowest order bit
corresponding to the first logical CPU and the highest order bit corresponding
to the last logical CPU.  Not all CPUs may exist on a given system but a mask
may specify more CPUs than are present.  A retrieved mask will reflect only the
bits that correspond to CPUs physically on the system.  If an invalid mask is
given (i.e., one that corresponds to no valid CPUs on the current system) an
error is returned.  The masks are typically given in hexadecimal.  For example,
.TP
.BR 0x00000001
is processor #0
.TP
.BR 0x00000003
is processors #0 and #1
.TP
.BR 0xFFFFFFFF
is all processors (#0 through #31)
.PP
When
.BR taskset
returns, it is guaranteed that the given program has been scheduled to a legal
CPU.
.SH OPTIONS
.TP
.BR \-p ,\  \-\-pid
operate on an existing PID and not launch a new task
.TP
.BR \-c ,\  \-\-cpu-list
specify a numerical list of processors instead of a bitmask.  The list may
contain multiple items, separated by comma, and ranges.  For example,
.BR 0,5,7,9-11 .
.TP
.BR \-h ,\  \-\-help
display usage information and exit
.TP
.BR \-V ,\  \-\-version
output version information and exit
.SH USAGE
.TP
The default behavior is to run a new command with a given affinity mask:
.B taskset
.I mask
.IR command\  [ arguments ]
.TP
You can also retrieve the CPU affinity of an existing task:
.B taskset \-p
.I pid
.TP
Or set it:
.B taskset \-p
.I mask pid
.SH PERMISSIONS
A user must possess
.B CAP_SYS_NICE
to change the CPU affinity of a process.  Any user can retrieve the affinity
mask.
.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 chrt (1),
.BR nice (1),
.BR renice (1),
.BR sched_setaffinity (2),
.BR sched_getaffinity (2)
.sp
See
.BR sched_setscheduler (2)
for a description of the Linux scheduling scheme.
.SH AVAILABILITY
The taskset command is part of the util-linux-ng package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.