NAME
getpriority,
setpriority —
get/set program scheduling
priority
LIBRARY
Standard C Library (libc, -lc)
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()
system call and set with the
setpriority()
system call. The which argument 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. The prio argument is a value in the range -20 to
20. The default priority is 0; lower priorities cause more favorable
scheduling.
The
getpriority()
system call returns the highest priority (lowest numerical value) enjoyed by
any of the specified processes. The
setpriority()
system call sets the priorities of all of the specified processes to the
specified value. Only the super-user 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() function returns the value 0
if successful; otherwise the value -1 is returned and the global
variable errno is set to indicate the error.
ERRORS
The getpriority() and
setpriority() system calls will fail if:
- [
ESRCH] - No process was located using the which and who values specified.
- [
EINVAL] - The which argument was not one of
PRIO_PROCESS,PRIO_PGRP, orPRIO_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 priority.
SEE ALSO
HISTORY
The getpriority() system call appeared in
4.2BSD.