nice [priorityincr]
Changes or returns the process priority. If priorityincr is omitted, the current priority is returned. If priorityincr is positive, it is added to the current priority level, up to a system defined maximum (normally 19).
Negative priorityincr values cumulatively increase the program's priority down to a system defined minimum (normally -19); increasing priority with negative niceness values will only work for the superuser.
The new priority is returned.