Name
getpriority, setpriority — get/set program
scheduling priority
Synopsis
int
getpriority( |
int |
which, |
| |
int |
who); |
int
setpriority( |
int |
which, |
| |
int |
who, |
| |
int |
prio); |
DESCRIPTION
The scheduling priority of the process, process group, or
user, as indicated by which and who is obtained with the
getpriority() call and set with
the setpriority() call.
The value which is
one of PRIO_PROCESS,
PRIO_PGRP, or PRIO_USER, and who is interpreted relative to
which (a process
identifier for PRIO_PROCESS,
process group identifier for PRIO_PGRP, and a user ID for PRIO_USER). A zero value for who denotes (respectively) the
calling process, the process group of the calling process, or
the real user ID of the calling process. Prio is a value in the range
−20 to 19 (but see the Notes below). The default
priority is 0; lower priorities cause more favorable
scheduling.
The getpriority() call
returns the highest priority (lowest numerical value) enjoyed
by any of the specified processes. The setpriority() call sets the priorities of
all of the specified processes to the specified value. Only
the superuser may lower priorities.
RETURN VALUE
Since getpriority() can
legitimately return the value −1, it is necessary to
clear the external variable errno prior to the call, then check it
afterwards to determine if a −1 is an error or a
legitimate value. The setpriority() call returns 0 if there is no
error, or −1 if there is.
ERRORS
- EINVAL
-
which was
not one of PRIO_PROCESS,
PRIO_PGRP, or
PRIO_USER.
- ESRCH
-
No process was located using the which and who values specified.
In addition to the errors indicated above, setpriority() may fail if:
- EPERM
-
A process was located, but its effective user ID did
not match either the effective or the real user ID of
the caller, and was not privileged (on Linux: did not
have the CAP_SYS_NICE
capability). But see NOTES below.
- EACCES
-
The caller attempted to lower a process priority,
but did not have the required privilege (on Linux: did
not have the CAP_SYS_NICE
capability). Since Linux 2.6.12, this error only occurs
if the caller attempts to set a process priority
outside the range of the RLIMIT_NICE soft resource limit of
the target process; see getrlimit(2) for
details.
CONFORMING TO
SVr4, 4.4BSD (these function calls first appeared in
4.2BSD), POSIX.1-2001.
NOTES
A child created by fork(2) inherits its
parent's nice value. The nice value is preserved across
execve(2).
The details on the condition for EPERM depend on the
system. The above description is what POSIX.1-2001 says, and
seems to be followed on all System V-like systems. Linux
kernels before 2.6.12 required the real or effective user ID
of the caller to match the real user of the process
who (instead of its
effective user ID). Linux 2.6.12 and later require the
effective user ID of the caller to match the real or
effective user ID of the process who. All BSD-like systems
(SunOS 4.1.3, Ultrix 4.2, 4.3BSD, FreeBSD 4.3, OpenBSD-2.5,
...) behave in the same manner as Linux >= 2.6.12.
The actual priority range varies between kernel versions.
Linux before 1.3.36 had −infinity..15. Since kernel
1.3.43 Linux has the range −20..19. Within the kernel,
nice values are actually represented using the corresponding
range 40..1 (since negative numbers are error codes) and
these are the values employed by the setpriority() and getpriority() system calls. The glibc
wrapper functions for these system calls handle the
translations between the user-land and kernel representations
of the nice value according to the formula unice = 20 − knice.
On some systems, the range of nice values is
−20..20.
Including <sys/time.h> is not
required these days, but increases portability. (Indeed,
<sys/resource.h>
defines the rusage
structure with fields of type struct timeval defined in
<sys/time.h>.)
SEE ALSO
nice(1), fork(2), capabilities(7), renice(8)
Copyright (c) 1980, 1991 The Regents of the University of California.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. All advertising materials mentioning features or use of this software
must display the following acknowledgement:
This product includes software developed by the University of
California, Berkeley and its contributors.
4. Neither the name of the University nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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SUCH DAMAGE.
@(#)getpriority.2
6.9 (Berkeley) 3/10/91
Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
Modified 1996-07-01 by Andries Brouwer <aeb@cwi.nl>
Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
Modified 2001-10-21 by Michael Kerrisk <mtk-manpages@gmx.net>
Corrected statement under EPERM to clarify privileges required
Modified 2002-06-21 by Michael Kerrisk <mtk-manpages@gmx.net>
Clarified meaning of 0 value for 'who' argument
Modified 2004-05-27 by Michael Kerrisk <mtk-manpages@gmx.net>
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