Customizing the Boot Process

It is possible to add your own item to the boot process. There are three standard ways of configuring this to avoid conflict with standard software:

• create your own upstart job or configure upstart to run an external script for you.

• create a subsystem of your own. This is useful especially if your customization involves a daemon process. If the program is not already packaged as a subsystem you can create your own by taking a simple subsystem script and modifying it.

• if your modifications consist of some commands that simply must be run as part of the startup process, you can use the existing (empty) rc.local script. This script is executed as if it is a subsystem if it is configured with start links in the rcX.d directories. Note that this script isn't really a subsystem, so start links are really a misnomer. Since the rc.local script is just a bunch of commands to execute, it ignores the start and stop arguments. Irrespective of their names, symlinks are just used to trigger the execution of the script. Thus, since all symlinks are implicitly start links, they should always be prefixed with S.

When installed, the rc.local script is empty, and it is configured to be started at all multiuser runlevels with the latest start order possible:

$ cd /etc/rc.d
$ ls -l rc.local rc?.d/*local
lrwxrwxrwx 1 root root  11 Jun  1  2008 rc2.d/S99local -> ../rc.local
lrwxrwxrwx 1 root root  11 Jun  1  2008 rc3.d/S99local -> ../rc.local
lrwxrwxrwx 1 root root  11 Jun  1  2008 rc4.d/S99local -> ../rc.local
lrwxrwxrwx 1 root root  11 Jun  1  2008 rc5.d/S99local -> ../rc.local
-rwxr-xr-x 1 root root 220 Mar  3  2008 rc.local

And it contains:

$ more rc.local
#!/bin/sh
#
# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here if you don't
# want to do the full Sys V style init stuff.

touch /var/lock/subsys/local
$

Copyright 2011 Greg Boyd - All Rights Reserved.