GETPRIORITY(2) BSD System Calls Manual GETPRIORITY(2)
getpriority, setpriority -- get/set process scheduling priority
getpriority(int which, id_t who);
setpriority(int which, id_t who, int prio);
The scheduling priority of the process, process group, or user, as indi-
cated 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.
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.
getpriority() and setpriority() will fail if:
[ESRCH] No process was located using the which and who values
[EINVAL] which was not one of PRIO_PROCESS, PRIO_PGRP, or
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
[EACCES] A non-superuser attempted to lower a process priority.
nice(1), fork(2), renice(8)
The getpriority() and setpriority() functions conform to IEEE Std
The predecessor of these functions, the former nice() system call,
appeared in Version 3 AT&T UNIX and was removed in 4.3BSD-Reno. The
getpriority() and setpriority() system calls appeared in 4.1cBSD.
BSD July 17, 2013 BSD