GETPRIORITY(2)

NAME
getpriority, setpriority - get/set program scheduling priority

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 the getpriority() 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, or PRIO_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
nice(1), fork(2), sched(3), renice(8)

HISTORY
The getpriority() function call appeared in 4.2BSD.