init program
Running a shell or even a shell script at boot time is fine for simple cases, but really, you need something more flexible. Normally, Unix systems run a program called init that starts up and monitors other programs. Over the years, there have been many init programs, some of which I will describe in Chapter 13. For now, I will briefly introduce BusyBox init.
The init program begins by reading the /etc/inittab configuration file. Here is a simple example, which is adequate for our needs:
::sysinit:/etc/init.d/rcS
::askfirst:-/bin/ash
The first line runs a shell script named rcS when init is started. The second line prints the message Please press Enter to activate this console to the console and starts a shell when you press Enter. The leading - before /bin/ash means that it will become a login shell, which sources /etc/profile and $HOME/.profile before displaying the shell prompt.
One of the advantages of launching the shell like this is that job control...
