GETPRIORITY(2) BSD System Calls Manual GETPRIORITY(2)
getpriority, setpriority -- get/set program scheduling priority
Standard C Library (libc, -lc)
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 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. 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 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
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 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.
nice(1), fork(2), renice(8)
The getpriority() function call appeared in 4.2BSD.
April 25, 2004 BSD