mirror of https://github.com/mkerrisk/man-pages
212 lines
6.6 KiB
Groff
212 lines
6.6 KiB
Groff
.\" Copyright (c) 1980, 1991 The Regents of the University of California.
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getpriority.2 6.9 (Berkeley) 3/10/91
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.\"
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.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
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.\" Modified 1996-07-01 by Andries Brouwer <aeb@cwi.nl>
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.\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 2001-10-21 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Corrected statement under EPERM to clarify privileges required
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.\" Modified 2002-06-21 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Clarified meaning of 0 value for 'who' argument
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.\" Modified 2004-05-27 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\"
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.TH GETPRIORITY 2 2002-09-20 "BSD Man Page" "Linux Programmer's Manual"
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.SH NAME
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getpriority, setpriority \- get/set program scheduling priority
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.SH SYNOPSIS
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.B #include <sys/time.h>
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.br
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.B #include <sys/resource.h>
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.sp
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.BI "int getpriority(int " which ", int " who );
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.br
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.BI "int setpriority(int " which ", int " who ", int " prio );
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.SH DESCRIPTION
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The scheduling priority of the process, process group, or user, as
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indicated by
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.I which
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and
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.I who
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is obtained with the
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.BR getpriority ()
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call and set with the
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.BR setpriority ()
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call.
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The value
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.I which
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is one of
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.BR PRIO_PROCESS ,
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.BR PRIO_PGRP ,
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or
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.BR PRIO_USER ,
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and
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.I who
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is interpreted relative to
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.I which
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(a process identifier for
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.BR PRIO_PROCESS ,
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process group
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identifier for
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.BR PRIO_PGRP ,
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and a user ID for
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.BR PRIO_USER ).
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A zero value for
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.I who
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denotes (respectively) the calling process, the process group of the
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calling process, or the real user ID of the calling process.
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.I Prio
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is a value in the range \-20 to 19 (but see the Notes below).
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The default priority is 0;
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lower priorities cause more favorable scheduling.
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The
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.BR 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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.BR 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 superuser may lower priorities.
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.SH "RETURN VALUE"
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Since
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.BR 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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.I errno
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prior to the
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call, then check it afterwards 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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.BR 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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.TP
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.B EINVAL
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.I which
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was not one of
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.BR PRIO_PROCESS ,
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.BR PRIO_PGRP ,
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or
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.BR PRIO_USER .
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.TP
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.B ESRCH
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No process was located using the
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.I which
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and
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.I who
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values specified.
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.PP
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In addition to the errors indicated above,
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.BR setpriority ()
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may fail if:
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.TP
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.B EPERM
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A process was located, but its effective user ID did not match
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either the effective or the real user ID of the caller,
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and was not privileged (on Linux: did not have the
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.B CAP_SYS_NICE
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capability).
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But see NOTES below.
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.TP
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.B EACCES
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The caller attempted to lower a process priority, but did not
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have the required privilege (on Linux: did not have the
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.B CAP_SYS_NICE
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capability).
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Since Linux 2.6.12, this error only occurs if the caller attempts
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to set a process priority outside the range of the
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.B RLIMIT_NICE
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soft resource limit of the target process; see
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.BR getrlimit (2)
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for details.
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.SH NOTES
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A child created by
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.BR fork (2)
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inherits its parent's nice value.
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The nice value is preserved across
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.BR execve (2).
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The details on the condition for EPERM depend on the system.
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The above description is what POSIX.1-2001 says, and seems to be followed on
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all System V-like systems.
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Linux kernels before 2.6.12 required the real or
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effective user ID of the caller to match
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the real user of the process \fIwho\fP (instead of its effective user ID).
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Linux 2.6.12 and later require
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the effective user ID of the caller to match
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the real or effective user ID of the process \fIwho\fP.
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All BSD-like systems (SunOS 4.1.3, Ultrix 4.2,
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4.3BSD, FreeBSD 4.3, OpenBSD-2.5, ...) behave in the same
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manner as Linux >= 2.6.12.
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.LP
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The actual priority range varies between kernel versions.
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Linux before 1.3.36 had \-infinity..15.
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Since kernel 1.3.43 Linux has the range \-20..19.
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Within the kernel, nice values are actually represented
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using the corresponding range 40..1
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(since negative numbers are error codes) and these are the values
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employed by the
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.BR setpriority ()
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and
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.BR getpriority ()
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system calls.
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The glibc wrapper functions for these system calls handle the
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translations between the user-land and kernel representations
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of the nice value according to the formula
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.IR "unice\ =\ 20\ \-\ knice" .
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.LP
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On some systems, the range of nice values is \-20..20.
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.LP
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Including
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.I <sys/time.h>
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is not required these days, but increases portability.
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(Indeed,
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.I <sys/resource.h>
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defines the
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.I rusage
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structure with fields of type
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.I struct timeval
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defined in
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.IR <sys/time.h> .)
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.SH "CONFORMING TO"
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SVr4, 4.4BSD (these function calls first appeared in 4.2BSD),
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POSIX.1-2001.
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.SH "SEE ALSO"
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.BR nice (1),
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.BR fork (2),
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.BR capabilities (7),
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.BR renice (8)
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