GETPRIORITY(2) — SYSTEM CALLS
NAME
getpriority, setpriority − get/set program scheduling priority
SYNOPSIS
#include <sys/time.h>
#include <sys/resource.h>
int getpriority(which, who)
int which, who;
int setpriority(which, who, prio)
int which, who, 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. Priorities are values in the range −20 to 20. The default priority is 0; lower priorities cause more favorable scheduling.
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.
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 value specified by prio. If prio is less than −20, a value of −20 is used; if it is greater than 20, a value of 20 is used. Only the super-user may lower priorities.
RETURN VALUE
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() may return one of the following errors:
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() may fail with one of the following errors returned:
EPERM A process was located, but neither its effective nor real user ID matched the effective user ID of the caller, and neither the effective nor the real user ID of the process executing the setpriority() was super-user.
EACCES The call to getpriority() would have changed a process’ priority to a value lower than its current value, and the effective user ID of the process executing the call was not that of the super-user.
SEE ALSO
BUGS
It is not possible for the process executing setpriority() to lower any other process down to its current priority, without requiring super-user privileges.
Sun Release 4.0 — Last change: 20 November 1987