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GETPRIORITY(2) |
System Calls Manual |
GETPRIORITY(2) |
NAME
getpriority, setpriority — get/set program scheduling priority
LIBRARY
Standard C Library (libc, -lc)
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. 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.
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 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.
HISTORY
The getpriority() function call appeared in 4.2BSD.