10.6 It looks as if Debian does not use rc.local to customize the boot process; what facilities are provided?

Suppose a system needs to execute script foo on start-up, or on entry to a particular (System V) runlevel. Then the system administrator should:

• Enter the script foo into the directory /etc/init.d/.

• Run the Debian command update-rc.d with appropriate arguments, to set up links between the (command-line-specified) directories rc?.d and /etc/init.d/foo. Here, '?' is a number from 0 through 6 and corresponds to each of the System V runlevels.

• Reboot the system.

The command update-rc.d will set up links between files in the directories rc?.d and the script in /etc/init.d/. Each link will begin with a 'S' or a 'K', followed by a number, followed by the name of the script. Scripts beginning with 'S' in /etc/rcN.d/ are executed when runlevel N is entered. Scripts beginning with a 'K' are executed when leaving runlevel N.

One might, for example, cause the script foo to execute at boot-up, by putting it in /etc/init.d/ and installing the links with update-rc.d foo defaults 19. The argument 'defaults' refers to the default runlevels, which are 2 through 5. The argument '19' ensures that foo is called before any scripts containing numbers 20 or larger.