PID

A process is the instance of a program which is executed, and each process in the operating system is assigned a unique PID. Every PID is always a non-negative integer. The PID is not constant for all the processes as PID is assigned based on the order of the execution since the system is started. But, init is the only process which has a constant PID as no matter whenever a system is started, init is the very first process that runs in a computer, and it is always assigned 1. By default the maximum value for a PID is 32,767 as it is the maximum number of process that can exist on a system at the same time.