GETPRIORITY(2)

NAME
getpriority, setpriority - get/set process scheduling priority

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. 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. Priority values outside the range -20 to 20 are truncated to the appropriate limit. Only the superuser 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() call returns 0 if there is no error, or -1 if there is.

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, or PRIO_USER.

In addition, 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-superuser attempted to lower a process priority.

SEE ALSO
nice(1), fork(2), renice(8)

STANDARDS
The getpriority() and setpriority() functions conform to p1003.1-2008.

HISTORY
The predecessor of these functions, the former nice() system call, appeared in AT&T UNIX and was removed in 4.3BSD Reno. The getpriority() and setpriority() system calls appeared in 4.1cBSD.