Etckeeper puts /etc under revision control, git by default, which then behaves like a normal git repository.

Once installed, an admin needs to run etckeeper init to initialize /etc/.git, and then invoke cd /etc/; git commit -am "Initial commit" to complete the install.

After that, you can cd /etc, and then execute the most useful commands:

 git log                         (see commit dates & commit msgs)
 git log -p                      (see commits with diff included)
 git add FILE...                 (add FILE to git)
 git diff                        (see any differences since last commit)
 git commit -am "Commit message" (commit your changes after modification)
 git checkout FILE               (override FILE with version from last commit)

1. Usage

Each time you make a change and are happy with it, run commit like git commit -am "changed blah blah".

2. Notes

EtcKeeper is better than custom solutions as it also adds apt hooks, so the files are added and commited to git automatically before/after apt-get installs.