ultrix man page for setpriority

getpriority(2)							System Calls Manual						    getpriority(2)

Name
       getpriority, setpriority - get or set program scheduling priority

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

       #define PRIO_PROCESS	0    /* process */
       #define PRIO_PGRP	1    /* process group */
       #define PRIO_USER	2    /* user id */

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

       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 call and set with the
       call.  The 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).  The prio is a value in the range -20 to 20.  The
       default priority is 0; lower priorities cause more favorable scheduling.

       The call returns the highest priority (lowest numerical value) enjoyed by any of the specified processes.  The call sets the priorities	of
       all of the specified processes to the specified value.  Only the superuser may lower priorities.

Return Values
       Since 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 call returns 0 if there is no error or -1 if there is.

Diagnostics
       The and system calls fail under the following conditions:

       [ESRCH]	      No processes were located using the which and who values specified.

       [EINVAL]       The which was not one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER.

       In addition to the errors indicated above, setpriority can fail under the following conditions:

       [EPERM]	      A process was located, but neither its effective nor real user ID matched the effective user ID of the caller.

       [EACCES]       A user other than the superuser attempted to change a process priority to a negative value.

See Also
       nice(1), fork(2), renice(8)

																    getpriority(2)