Generate a diff between current /etc/ and default configuration

Question

After installation and various custom configurations, is it possible to use eg. apt and some shell-fu to produce a diff for every file in /etc/ that differs from the standard configuration? This would provide a means to generate a short summary of the configuration state after the fact, rather than having to rely on manual logging along the way, should one desire to remember what was changed at a later time.

Answer 1

You should take a look to etckeeper :

etckeeper is a collection of tools to let /etc be stored in a git, mercurial, darcs, or bzr repository. It hooks into apt (and other package managers including yum and pacman-g2) to automatically commit changes made to /etc during package upgrades. It tracks file metadata that revison control systems do not normally support, but that is important for /etc, such as the permissions of /etc/shadow. It's quite modular and configurable, while also being simple to use if you understand the basics of working with revision control.

Answer 2

I'm in the middle of developing a solution to the same kind of problem.

Basically, my objective is a system allowing undo and redo with file-level granularity.

Starting with your question and working backwards...

• In order to compare to the default configuration, we have to store the originals of all those files somewhere first. Then we can produce what you want with something like...

DIFFDIR= ......
ARCDIR=./.archives                         # see below

function getlastarchive() {
  ... code to return last archived version ...
}

for FILE in /etc/*
do
  ARCFILE="$(getlastarchive $FILE)"
  diff $ARCDIR/$ARCFILE /etc/$FILE  >$DIFFDIR/$FILE.diff
done

• To store the originals, I've chosen to adopt the convention of having a single .archives subdirectory in any directory with an altered file. It's created as necessary by a file-archive script.
• If you only want one level of undo, you only need copy the unaltered file to the .archives directory before it is changed.
• For unlimited-undo, we need a versioning scheme. An obvious choice is a datetime stamp appended to the name of the archived version. Something like...

Files:                      /etc/hosts
                            /etc/resolv.conf

Archived Versions:          /etc/.archives/hosts.20121219015459
                            /etc/.archives/resolv.conf.20121219015459

• Instead, I'm using just an auto-calculated incremental version#, as in...

Files:                      /etc/hosts
                            /etc/resolv.conf

Archived Versions:          /etc/.archives/hosts.00
                            /etc/.archives/resolv.00.conf

• The version# is before the extension since I also use this for edited versions of images which need their extensions (.jpg, .png, etc) intact in order to be detected properly by a lot of software. If a file has no extension, the version# is just appended to the end. The code to do this is more complex, but runs instantly so no problem. A case can be made for a number of other schemes but this works for me.

Hope this helps!