NAME
getpriority,
setpriority —
get/set program scheduling
priority
LIBRARY
library “libc”
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 thegetpriority()
call and set with the
setpriority()
call.
The priority is maintained in a per-process basis and affects
scheduling of LWPs which belong to the process and use the
SCHED_OTHER scheduling class.
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; numerically lower priority values cause more
favorable scheduling. A value of 19 or 20 will schedule a process only when
nothing at priority ≤ 0 is runnable.
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 priority values.
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:
- [
EINVAL] - which was not one of
PRIO_PROCESS,PRIO_PGRP, orPRIO_USER. - [
ESRCH] - No process was located using the which and who values specified.
In addition to the errors indicated above,
setpriority() will fail if:
- [
EACCES] - A non super-user attempted to lower a process priority value.
- [
EPERM] - A process was located, but neither its effective nor real user ID matched the effective user ID of the caller.
SEE ALSO
HISTORY
The getpriority() function call appeared
in 4.2BSD.