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NAME

     getpriority, setpriority - get/set program scheduling priority

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

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

     int
     getpriority(int which, int who);

     int
     setpriority(int which, int 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() system call
     and set with the setpriority() system call.  The which argument 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 prio argument is a
     value in the range -20 to 20.  The default priority is 0; lower
     priorities cause more favorable scheduling.

     The getpriority() system call returns the highest priority (lowest
     numerical value) enjoyed by any of the specified processes.  The
     setpriority() system 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() function returns the value 0 if successful; otherwise
     the value -1 is returned and the global variable errno is set to indicate
     the error.

ERRORS

     The getpriority() and setpriority() system calls will fail if:

     [ESRCH]            No process was located using the which and who values
                        specified.

     [EINVAL]           The which argument 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.

SEE ALSO

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

HISTORY

     The getpriority() system call appeared in 4.2BSD.