BusyBox init

BusyBox has a minimal init program that uses a configuration file, /etc/inittab,
to define rules to start programs at bootup and to stop them at shutdown. Usually,
the actual work is done by shell scripts, which, by convention, are placed in the
/etc/init.d directory.

init begins by reading /etc/inittab. This contains a list of programs to run, one per line, with this format:

<id>::<action>:<program>

The role of these parameters is as follows:

• id: This is the controlling terminal for the command.
• action: This includes the conditions to run this command, as shown in the following list.
• program: This is the program to run.

The actions are as follows:

• sysinit: Runs the program when init starts before any of the other types
  of actions.
• respawn: Runs the program and restarts it if it terminates. It is typically used to run a program as a daemon.
• askfirst: This is the same as respawn, but it prints the message...