NAME

getpriority, setpriority − get/set process nice value

SYNOPSIS

#include <sys/time.h>
#include <sys/resource.h>

int getpriority(which, who)
int which, who;

int setpriority(which, who, niceval)
int which, who, niceval;

DESCRIPTION

The nice value of a process, process group, or user, as indicated by which and who is obtained with the getpriority() call and set with the setpriority() call.  Process nice values can range from −20 through 19.  The default nice value is 0; lower nice values 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 lowest numerical nice value of any of the specified processes.  The setpriority() call sets the nice values of all of the specified processes to the value specified by niceval. If niceval is less than −20, a value of −20 is used; if it is greater than 19, a value of 19 is used.  Only the super-user may use negative nice values. 

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’ nice value 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

nice(1), ps(1), fork(2), nice(3C) renice(8)

Writing Device Drivers

BUGS

It is not possible for the process executing setpriority() to lower any other process down to its current nice value, without requiring super-user privileges. 

These system calls are misnamed.  They get and set the nice value, not the kernel scheduling priority.  nice(1) discusses the relationship between nice value and scheduling priority. 
 

Sun Release 4.0  —  Last change: 10 May 1989