GETPRIORITY(2) System Calls Manual GETPRIORITY(2)
getpriority, setpriority - get/set process nice value
int getpriority(which, who)
int which, who;
int setpriority(which, who, niceval)
int which, who, niceval;
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
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
The getpriority() call returns the lowest numerical nice value of any
of the specified processes. The setpriority() call sets the nice val-
ues of all of the specified processes to the value specified by nice-
val. 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.
Since getpriority() can legitimately return the value -1, it is neces-
sary 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.
0 on success.
-1 on failure and sets errno to indicate the error.
getpriority() and setpriority() may set errno to:
EINVAL which was not one of PRIO_PROCESS, PRIO_PGRP, or
ESRCH No process was located using the which and who values
In addition to the errors indicated above, setpriority() may fail with
one of the following errors returned:
EACCES The call to setpriority() 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.
EPERM A process was located, but neither its effective nor
real user ID matched the effective user ID of the call-
er, and neither the effective nor the real user ID of
the process executing setpriority() was super-user.
nice(1), ps(1), fork(2V), nice(3v) renice(8)
It is not possible for the process executing setpriority() to lower any
other process down to its current nice value, without requiring super-
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.
21 January 1990 GETPRIORITY(2)