nice - change priority of process

Syntax	#include <unistd.h> int nice(int incr);
Description	nice() adds the value of incr to the nice value of the calling process. Note that in the C runtime system, changing the nice value with incr has no effect on the priority of a process. The function is supported only for conformance with XPG4. A process nice value is a non-negative integer for which a more positive value results in lower CPU priority. A maximum nice value of 2*{NZERO}-1 and a minimum nice value of 0 are imposed by the system. Requests for values above or below these limits result in the nice value being set to the corresponding limit. Only a process with appropriate privileges can lower the nice value. If threads are used, then the function affects the process or a thread in the following manner: Changes the priority of a process. If the process is multithreaded, the scheduling priority affects all threads of the process throughout the scope of the system.
Return val.	New nice value minus {NZERO}
		upon successful completion.
	-1	if an error occurs. The process nice value is not changed, and errno is set to indicate the error.
Errors	nice() will fail if:
	EPERM	incr is negative or greater than 2*{NZERO}-1, and the calling process does not have appropriate privileges.
Notes	As -1 is a permissible return value in a successful situation, an application wishing to check for error situations should set errno to 0, then call nice(), and if it returns -1, check to see if errno is non-zero.
See also	limits.h, unistd.h.