There are other ways to start up applications; indeed, you can do this by placing an entry in inittab. On a couple of systems I look after, I have entries in inittab, not because these systems do not have run level directories, but because I have a few system checker scripts that I want to be run as soon as the system has finished coming up. Inittab is an ideal place to put these.
For this example we’ll use one of my disk mirror check scripts that is run as soon as we are in run level 3. First I make sure the script runs properly, then make a backup copy of inittab.
$ cp /etc/inittab /etc/inittab.bak
Next edit inittab. I make the following entry at the end of the file.
# disk checker script, let’s ...