Process identifier
A process identifier ( process ID , PID , German process identifier ) is in the computer science a unique key , which is the unique identification of processes used. The PID does not change during the runtime of the process.
Most operating systems (e.g. Unix , Windows ) use a natural number for this . Process IDs are mainly required for interprocess communication .
UNIX
After the process has ended, the process becomes a zombie and the parent process (identified by the Parent Process ID , PPID for short ) can query the status. Only then is the PID free again for new processes.
example
The Bourne-again shell runs as a process on a Unix system. A unique PID is assigned to this process (for example: 3139). If you start another so-called child process from this process, it will now run with its own PID (for example: 4171) under the PPID of the parent process (3139).
