192 lines
5.5 KiB
Groff
192 lines
5.5 KiB
Groff
.\" chrt(1) manpage
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.\"
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.\" Copyright (C) 2004 Robert Love
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.\" Copyright (C) 2015 Karel Zak <kzak@redhat.com>
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.\"
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License,
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.\" version 2, as published by the Free Software Foundation.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public License along
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.\" with this program; if not, write to the Free Software Foundation, Inc.,
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.\" 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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.\"
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.TH CHRT 1 "January 2016" "util-linux" "User Commands"
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.SH NAME
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chrt \- manipulate the real-time attributes of a process
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.SH SYNOPSIS
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.B chrt
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[options]
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.IR priority\ command\ [ argument ...]
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.br
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.B chrt
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[options]
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.B \-p
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.RI [ priority ]\ pid
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.SH DESCRIPTION
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.B chrt
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sets or retrieves the real-time scheduling attributes of an existing \fIpid\fR,
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or runs \fIcommand\fR with the given attributes.
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.SH POLICIES
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.TP
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\fB\-o\fR, \fB\-\-other\fR
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Set scheduling policy to \fBSCHED_OTHER\fR (time-sharing scheduling).
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This is the default Linux scheduling policy.
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.TP
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\fB\-f\fR, \fB\-\-fifo\fR
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Set scheduling policy to \fBSCHED_FIFO\fR (first in-first out).
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.TP
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\fB\-r\fR, \fB\-\-rr\fR
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Set scheduling policy to \fBSCHED_RR\fR (round-robin scheduling).
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When no policy is defined, the
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.B SCHED_RR
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is used as the default.
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.TP
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\fB\-b\fR, \fB\-\-batch\fR
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Set scheduling policy to \fBSCHED_BATCH\fR (scheduling batch processes).
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Linux-specific, supported since 2.6.16. The priority argument has to be set to zero.
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.TP
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\fB\-i\fR, \fB\-\-idle\fR
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Set scheduling policy to \fBSCHED_IDLE\fR (scheduling very low priority jobs).
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Linux-specific, supported since 2.6.23. The priority argument has to be set to zero.
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.TP
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.BR \-d ,\ \-\-deadline
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Set scheduling policy to \fBSCHED_DEADLINE\fR (sporadic task model deadline scheduling).
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Linux-specific, supported since 3.14. The priority argument has to be set to zero.
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See also \fB\-\-sched\-runtime\fR, \fB\-\-sched\-deadline\fR and
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\fB\-\-sched\-period\fR. The relation between the options required by the kernel is
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runtime <= deadline <= period.
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.B chrt
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copies \fIperiod\fR to \fIdeadline\fR if \fB\-\-sched\-deadline\fR is not specified and
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\fIdeadline\fR to \fIruntime\fR if \fB\-\-sched\-runtime\fR is not specified.
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It means that at least \fB\-\-sched\-period\fR has to be specified. See
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.BR sched (7)
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for more details.
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.SH SCHEDULING OPTIONS
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.TP
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\fB\-T\fR, \fB\-\-sched\-runtime\fR \fInanoseconds\fR
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Specifies runtime parameter for SCHED_DEADLINE policy (Linux-specific).
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.TP
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\fB\-P\fR, \fB\-\-sched\-period\fR \fInanoseconds\fR
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Specifies period parameter for SCHED_DEADLINE policy (Linux-specific).
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.TP
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\fB\-D\fR, \fB\-\-sched\-deadline\fR \fInanoseconds\fR
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Specifies deadline parameter for SCHED_DEADLINE policy (Linux-specific).
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.TP
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\fB\-R\fR, \fB\-\-reset-on-fork\fR
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Use
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.B SCHED_RESET_ON_FORK
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or
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.B SCHED_FLAG_RESET_ON_FORK
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flag. Linux-specific, supported since 2.6.31.
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Each thread has a reset-on-fork scheduling flag. When this flag is set, children created by
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.BR fork (2)
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do not inherit privileged scheduling policies. After the reset-on-fork flag has been enabled,
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it can be reset only if the thread has the
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.BR CAP_SYS_NICE
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capability. This flag is disabled in child processes created by
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.BR fork (2).
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More precisely, if the reset-on-fork flag is set,
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the following rules apply for subsequently created children:
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.RS
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.IP * 3
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If the calling thread has a scheduling policy of
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.B SCHED_FIFO
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or
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.BR SCHED_RR ,
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the policy is reset to
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.BR SCHED_OTHER
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in child processes.
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.IP *
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If the calling process has a negative nice value,
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the nice value is reset to zero in child processes.
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.RE
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.SH OPTIONS
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.TP
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.BR \-a ,\ \-\-all-tasks
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Set or retrieve the scheduling attributes of all the tasks (threads) for a
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given PID.
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.TP
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.BR \-m ,\ \-\-max
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Show minimum and maximum valid priorities, then exit.
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.TP
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.BR \-p ,\ \-\-pid
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Operate on an existing PID and do not launch a new task.
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.TP
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.BR \-v ,\ \-\-verbose
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Show status information.
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.TP
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.BR \-V ,\ \-\-version
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Display version information and exit.
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.TP
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.BR \-h ,\ \-\-help
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Display help text and exit.
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.SH USAGE
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.TP
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The default behavior is to run a new command:
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.B chrt
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.I priority
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.IR command\ [ arguments ]
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.TP
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You can also retrieve the real-time attributes of an existing task:
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.B chrt \-p
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.I pid
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.TP
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Or set them:
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.B chrt \-r \-p
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.I priority pid
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.SH PERMISSIONS
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A user must possess
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.B CAP_SYS_NICE
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to change the scheduling attributes of a process. Any user can retrieve the
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scheduling information.
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.SH NOTES
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Only
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.BR SCHED_FIFO ,
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.B SCHED_OTHER
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and
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.B SCHED_RR
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are part of POSIX 1003.1b Process Scheduling. The other scheduling attributes
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may be ignored on some systems.
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.P
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Linux' default scheduling policy is
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.BR SCHED_OTHER .
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.SH AUTHORS
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.UR rml@tech9.net
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Robert Love
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.UE
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.br
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.UR kzak@redhat.com
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Karel Zak
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.UE
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.SH SEE ALSO
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.BR nice (1),
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.BR renice (1),
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.BR taskset (1),
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.BR sched (7)
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.sp
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See
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.BR sched_setscheduler (2)
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for a description of the Linux scheduling scheme.
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.SH AVAILABILITY
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The chrt command is part of the util-linux package and is available from
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https://www.kernel.org/pub/linux/utils/util-linux/.
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