NAME
getpriority,
setpriority —
get/set program scheduling
priority
LIBRARY
library “libc”
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 thegetpriority()
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 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
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 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() function call appeared
in 4.2BSD.