getpriority, setpriority - get/set program scheduling pri
ority
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 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 pro
cesses. 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 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
ESRCH No process was located using the which and who val
ues specified.
EINVAL Which was not one of PRIO_PROCESS, PRIO_PGRP, or
PRIO_USER.
In addition to the errors indicated above, 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 super-user attempted to lower a process pri
ority.
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>.)
CONFORMING TO
SVr4, 4.4BSD (these function calls first appeared in
4.2BSD).
SEE ALSO
nice(1), fork(2), renice(8)
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