Each process has a priority that is determined by the niceness scale, which ranges from -20 to 19. The lower the nice value, the higher the priority of a process, so a nice value of -20 gives the highest priority to a process. On the other hand, a nice value of 19 gives the lowest priority to a process:
You might be asking yourself: Why do we care about a process priority? The answer is efficiency! Your CPU is like a waiter in a busy restaurant. An efficient waiter goes around all the time to ensure that all the customers are happily served. Similarly, your CPU allocates time to all processes running on your system. A process with a high priority gets a lot of attention from the CPU. On the other hand, a process with a low priority doesn't get as much attention from the CPU.
Viewing a process priority
Start Firefox as a background process:
elliot@ubuntu-linux:~$ firefox &
[1] 6849
You can use the ps command to view a...