Change the priority of a process
#include <unistd.h> int nice( int incr );
- The amount that you want to add to the process's priority.
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The nice() function allows a process to change its priority. The invoking process must be in a scheduling class that supports the operation.
The nice() function adds the value of incr to the nice value of the calling process. A process's nice value is a nonnegative number; a greater positive value results in a lower CPU priority.
A maximum nice value of 2 * NZERO - 1 and a minimum nice value of 0 are imposed by the system. NZERO is defined in <limits.h> with a default value of 20. If you request a value above or below these limits, the nice value is set to the corresponding limit. A nice value of 40 is treated as 39. Only a process with superuser privileges can lower the nice value.
The new nice value minus NZERO. If an error occurred, -1 is returned, the process's nice value isn't changed, and errno is set.
- The nice() function was called by a process in a scheduling class other than time-sharing.
- The incr argument was negative or greater than 40, and the effective user ID of the calling process isn't the superuser.
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 nonzero.