This section provides a quick introduction to a couple tools that might be useful for those who want more control over system configuration management. For larger needs, see Chapter 36, “Managing Sets of Servers.”
If you run Linux-based systems, you will find a series of directories that end with a .d and that store configuration files. These are sometimes called .d or “dot dee” directories. If you look in /etc/, you find many (such as apparmor.d and pam.d). Opening these directories reveals a large number of configuration files and perhaps other directories containing even more. In Ubuntu or other Debian-based systems, it is a violation of etiquette (and Debian policy) for any software package to be allowed to directly change the configuration files of another package. This can be problematic if you want to use system configuration management software.
dotdee solves this problem by allowing you to take any flat file in your filesystem and replace it with a symlink pointing to a file that is generated from a .d-style directory. It saves the original file and then updates the generated file automatically and dynamically any time any file in the original .d directory is added, deleted, or modified. This way, the Debian policy and general etiquette standards are met, but configurations can be modified as needed by an external program.
dotdee works its magic using inotify to dynamically and instantly update the master file. The master file can be built three different ways: using flat files, which are concatenated; using diff/patch files, which are applied in a quiltlike manner; and using executables, which process stdin and dump to stdout. This flexibility should make any system administrator or developer guru happy.