getpriority, setpriority - get/set program scheduling priority
#include <sys/time.h>
#include <sys/resource.h>
int getpriority(int which, int who);
int setpriority(int which, int 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.
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
afterwards 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.
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.
Including <sys/time.h> is not required these days, but increases portability.
(Indeed, <sys/resource.h> defines the rusage structure with
fields of type struct timeval defined in <sys/time.h>.)
SVr4, 4.4BSD (these function calls first appeared in 4.2BSD).
nice(1), fork(2), renice(8)
BSD Man Page 2001-06-19 GETPRIORITY(2)
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