NAME
getpriority,
setpriority —
get/set process scheduling
priority
SYNOPSIS
#include
<sys/resource.h>
int
getpriority(int
which, id_t
who);
int
setpriority(int
which, id_t 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. 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 of
who denotes the current process, process group, or
user. prio is a value in the range -20 to 20. 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. Priority values outside the range -20 to 20 are truncated to the
appropriate limit. Only the superuser may lower priorities.
RETURN VALUES
Since getpriority() can legitimately
return the value -1, it is necessary to clear the external variable
errno prior to the call, then check it afterward 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
getpriority() and
setpriority() will fail if:
- [
ESRCH] - No process was located using the which and who values specified.
- [
EINVAL] - which was not one of
PRIO_PROCESS,PRIO_PGRP, orPRIO_USER.
In addition, setpriority() will fail
if:
- [
EPERM] - A process was located, but neither its effective nor real user ID matched the effective user ID of the caller.
- [
EACCES] - A non-superuser attempted to lower a process priority.
SEE ALSO
STANDARDS
The getpriority() and
setpriority() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
HISTORY
The predecessor of these functions, the former
nice() system call, appeared in
Version 3 AT&T UNIX and was removed in
4.3BSD-Reno. The
getpriority() and
setpriority() system calls appeared in
4.1cBSD.