Shell Scripting: Expert Recipes for Linux, Bash, and More

Recipe 15-1: Installing Init Scripts

This recipe uses conditional execution — if, test, and case — to determine how to start up a process automatically at boot time. Most GNU/Linux systems today install init scripts into /etc/init.d, but not all, and the method of actually registering (if at all) and starting the process up differ between distributions. In Chapter 16, Recipe 16-1, “Init Scripts,” describes the init script itself.

Technologies Used

• if, else, elif
• case
• [ expression ] && command

Concepts

An init script is a simple shell script that starts up a service when the system boots up and shuts it down cleanly when the system is going down. This recipe is for a generic software installation routine to automatically install an init script when the software is installed outside of a package management system. http://lwn.net/Distributions lists over 500 different distributions. Most fall into one of a few categories (Red Hat–based, Debian-based, and so on) but a few are quite unique.

Potential Pitfalls

There are a few pitfalls for the script itself; the worst scenario is to fail without recognizing it and reporting the failure to the user. This script does make guesses on distros it does not successfully detect, but in its defense, it does display a message saying what it is doing. Following the normal Unix tradition, it is a very quiet script, totally silent on success, and displaying messages only when there is something to warn the user about or if something goes seriously ...