NICE(2) Linux Programmer's Manual NICE(2)
nice - change process priority
int nice(int inc);
nice adds inc to the nice value for the calling pid. (A large nice value means a low pri-
ority.) Only the superuser may specify a negative increment, or priority increase.
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
EPERM A non-super user attempts to do a priority increase by supplying a negative inc.
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
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.
nice(1), getpriority(2), setpriority(2), fork(2), renice(8)
Linux 2001-06-04 NICE(2)