get/set process scheduling
which, id_t who,
The scheduling priority of the process, process group, or user, as
indicated by which and who is
obtained with the
call and set with the
call. which is one of
PRIO_USER, and who is
interpreted relative to which (a process identifier
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.
call returns the highest priority (lowest numerical value) enjoyed by any of
the specified processes. The
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.
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.
setpriority() will fail if:
- No process was located using the which and who values specified.
- which was not one of
setpriority() will fail
- A process was located, but neither its effective nor real user ID matched the effective user ID of the caller.
- A non-superuser attempted to lower a process priority.
nice(1), fork(2), renice(8)
setpriority() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
The predecessor of these functions, the former
nice() system call, appeared in
Version 3 AT&T UNIX and was removed in
setpriority() system calls appeared in