All processes on a UNIX system come into being in the same way:
They are cloned from an already running process.
For example, suppose that a user types the command.
Every process on the system is numbered, starting from 1. This number is called the Process ID (PID). The ancestor of all processes on
the system is the process init, which is started at boot
time and is automatically given the PID of 1. All other processes
on the system are derived from init by the fork and exec procedures, either directly or indirectly. Because every process results from
, every process has a parent process, the process that called the
that created it. Because all
processes derive ultimately from init with PID 1, tracing the chain of ancestry back from any running process must ultimately lead to