GETPRIORITY(2) Linux Programmer's Manual GETPRIORITY(2)
NAME
getpriority, setpriority - get/set(7,n,1 builtins) program scheduling priority
SYNOPSIS
#include <sys/time.h>
#include <sys/resource.h>
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(7,n,1 builtins) 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(1,8) the range -20 to 20 (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 super-user may lower priorities.
RETURN VALUE
Since getpriority can legitimately return the value -1, it is necessary
to clear(1,3x,3x clrtobot) the external variable errno prior to the call, then check it
afterwards to determine if(3,n) a -1 is an error(8,n) or a legitimate value. The
setpriority call returns 0 if(3,n) there is no error(8,n), or -1 if(3,n) 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 (on
Linux systems) the caller did not have the CAP_SYS_NICE capabil-
ity.
EACCES A non super-user attempted to lower a process priority.
NOTES
The details on the condition for EPERM depend on the system. The above
description is what SUSv3 says, and seems to be followed on all SYSV-
like systems. Linux requires the real or effective user ID of the
caller to match the real user of the process who (instead of its effec-
tive user ID). All BSD-like systems (SunOS 4.1.3, Ultrix 4.2, BSD 4.3,
FreeBSD 4.3, OpenBSD-2.5, ...) require the effective user ID of the
caller to match the real or effective user ID of the process who.
The actual priority range varies between kernel versions. Linux before
1.3.36 had -infinity..15. Linux since 1.3.43 has -20..19, and the sys-
tem call getpriority returns 40..1 for these values (since negative
numbers are error(8,n) codes). The library call converts N into 20-N.
Including <sys/time.h> is not required these days, but increases porta-
bility. (Indeed, <sys/resource.h> defines the rusage structure with
fields of type struct timeval defined in(1,8) <sys/time.h>.)
CONFORMING TO
SVr4, 4.4BSD (these function calls first appeared in(1,8) 4.2BSD).
SEE ALSO
nice(1,2)(1), fork(2), capabilities(7), renice(8)
BSD Man Page 2002-06-21 GETPRIORITY(2)