Processes

The OS Scheduler, also called, idle process, has the

pid

of

0

. This process runs when no other processes are currently running on the CPU, and makes the decision of what process should run next on the CPU.

The process scheduler also launches a process called init (or systemd in newer Linux versions) with the

pid

of

1

, which runs throughout the entire execution of the OS. init creates all the other processes on the computer, thereby becoming the Great Parent of all processes.

• The Scheduler searches for the code of init in one of the following locations, in the given order:
  • /sbin/init:   the preferred and most likely location for the init program.
  • /etc/init:     another likely choice.
  • /bin/init:     a fallback choice.
  • /bin/sh:         last choice if the kernel fails to find an init process.
• If init is found, it initializes the system, starts various vital background services (= daemons), and launches a login process. Otherwise, if all the 4 init programs aren't found or fail to launch, the Linux kernel shuts the system down.