How it works internally
Nerd alert!) When a daemon program is started, it fires up a second
child process, detaches it, and then the parent process dies. This is
called forking. Because the parent process dies, it will give the
console back and it will look like nothing has happened. But wait:
the child process is still running. Even if you close your terminal,
the child continues to run in memory, until it either stops, crashes
or is killed.
In PHP: forking can be achieved by using the Process Control Extensions.
Getting a good grip on it, may take some studying though.