154 lines
4.1 KiB
Groff
154 lines
4.1 KiB
Groff
.\" $NetBSD: getpriority.2,v 1.20 2012/04/13 16:32:15 wiz Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getpriority.2 8.1 (Berkeley) 6/4/93
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.\"
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.Dd April 13, 2012
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.Dt GETPRIORITY 2
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.Os
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.Sh NAME
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.Nm getpriority ,
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.Nm setpriority
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.Nd get/set program scheduling priority
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/resource.h
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.Ft int
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.Fn getpriority "int which" "id_t who"
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.Ft int
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.Fn setpriority "int which" "id_t who" "int prio"
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.Sh DESCRIPTION
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The scheduling
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priority of the process, process group, or user, as indicated by
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.Fa which
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and
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.Fa who
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is obtained with the
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.Fn getpriority
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call and set with the
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.Fn setpriority
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call.
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.Pp
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The priority is maintained in a per-process basis and
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affects scheduling of LWPs which belong to the process and use the
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.Dv SCHED_OTHER
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scheduling class.
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.Pp
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.Fa which
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is one of
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.Dv PRIO_PROCESS ,
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.Dv PRIO_PGRP ,
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or
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.Dv PRIO_USER ,
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and
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.Fa who
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is interpreted relative to
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.Fa which
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(a process identifier for
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.Dv PRIO_PROCESS ,
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process group
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identifier for
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.Dv PRIO_PGRP ,
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and a user ID for
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.Dv PRIO_USER ) .
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A zero value of
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.Fa who
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denotes the current process, process group, or user.
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.Fa prio
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is a value in the range -20 to 20.
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The default priority is 0;
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numerically lower priority values cause more favorable scheduling.
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A value of 19 or 20
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will schedule a process only when nothing at priority \*(Le 0 is runnable.
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.Pp
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The
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.Fn getpriority
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call returns the highest priority (lowest numerical value)
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enjoyed by any of the specified processes.
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The
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.Fn setpriority
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call sets the priorities of all of the specified processes
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to the specified value.
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Only the super-user may lower priority values.
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.Sh RETURN VALUES
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Since
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.Fn getpriority
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can legitimately return the value \-1, it is necessary
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to clear the external variable
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.Va errno
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prior to the
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call, then check it afterward to determine
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if a \-1 is an error or a legitimate value.
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The
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.Fn setpriority
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call returns 0 if there is no error, or
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\-1 if there is.
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.Sh ERRORS
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.Fn getpriority
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and
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.Fn setpriority
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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.Fa which
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was not one of
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.Dv PRIO_PROCESS ,
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.Dv PRIO_PGRP ,
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or
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.Dv PRIO_USER .
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.It Bq Er ESRCH
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No process was located using the
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.Fa which
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and
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.Fa who
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values specified.
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.El
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.Pp
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In addition to the errors indicated above,
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.Fn setpriority
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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A non super-user attempted to lower a process priority value.
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.It Bq Er EPERM
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A process was located, but neither its effective nor real user
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ID matched the effective user ID of the caller.
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.El
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.Sh SEE ALSO
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.Xr nice 1 ,
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.Xr fork 2 ,
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.Xr sched 3 ,
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.Xr renice 8
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.Sh HISTORY
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The
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.Fn getpriority
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function call appeared in
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.Bx 4.2 .
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