System class

The system class uses a fixed-priority policy to run kernel processes such as servers and housekeeping processes like the paging demon. The system class is reserved for use by the kernel; users may neither add nor remove a process from the system class. Priorities for system class processes are set up in the kernel code for those processes; once established, the priorities of system processes do not change. (User processes and LWPs running in kernel mode are not in the system class.)