NAME
getpriority, setpriority - get/set program scheduling priority

SYNOPSIS
#include <sys/resource.h>

prio = getpriority(which, who)
int prio, which, who;

setpriority(which, who, prio)
int which, who, 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. Only the super-user 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 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 may return one of the following errors:

[ESRCH] No process was located using the which and who
values specified.

[EINVAL] Which was not one of PRIO_PROCESS, PRIO_PGRP, or
PRIO_USER.

In addition to the errors indicated above, setpriority may fail
with one of the following errors returned:

[EPERM] A process was located, but neither its effective nor
real user ID matched the effective user ID of the
caller.

[EACCES] A non super-user attempted to lower a process
priority.