redhat man page for nice

NICE(2) 						     Linux Programmer's Manual							   NICE(2)

NAME
       nice - change process priority

SYNOPSIS
       #include <unistd.h>

       int nice(int inc);

DESCRIPTION
       nice adds inc to the nice value for the calling pid.  (A large nice value means a low priority.)  Only the superuser may specify a negative
       increment, or priority increase.

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EPERM  A non-super user attempts to do a priority increase by supplying a negative inc.

CONFORMING TO
       SVr4, SVID EXT, AT&T, X/OPEN, BSD 4.3. However, the Linux and glibc (earlier than glibc 2.2.4) return  value  is  nonstandard,  see  below.
       SVr4 documents an additional EINVAL error code.

NOTES
       Note  that  the routine is documented in SUSv2 to return the new nice value, while the Linux syscall and (g)libc (earlier than glibc 2.2.4)
       routines return 0 on success.  The new nice value can be found using getpriority(2).  Note that an implementation in which nice returns the
       new  nice  value  can  legitimately  return -1.	To reliably detect an error, set errno to 0 before the call, and check its value when nice
       returns -1.

SEE ALSO
       nice(1), getpriority(2), setpriority(2), fork(2), renice(8)

Linux								    2001-06-04								   NICE(2)