Put /etc Under Revision Control (with git)

UPDATE: There is a much easier way now:

sudo aptitude install etckeeper

There, now etc is under revision control and changes are automatically committed with a helpful message after you install new packages. Thanks for the tip, Marcelo! Read on for the original blog entry.

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I put my /etc directory under revision control. I used git. It's awesome. Not that I think I'm going to wholesale copy my /etc from one machine to another, nor because I'm going to branch my /etc directory and spend weeks developing some cool new feature (whatever that would look like...) and then merge it back into the main branch. No, it's mostly because I like the idea of having the big "undo" option that having things under revision control provides. Having to commit changes and write check-in comments when I make changes helps me stay more organized too. It's never good when I go in willy-nilly to make a "quick change" to some configuration file.

I relied heavily on this blog entry for using git, and this blog entry for using mercurial (hg). I decided to go with git because mercurial quietly ignores symbolic links, and it seems like there are just a few important symbolic links in /etc. It also seems that git handles these just fine. Oh, and I didn't choose bzr or darcs mainly because they are slow, and because I want to get to know git better.

Here's how I did it (on Ubuntu Feisty Fawn, do all this as root):

First, initialize the repository:

cd /etc
git init-db
chmod og-rwx .git

The chmod is so non-root users can't go poking around in your repository. Next, ignore a few files:

cat > .gitignore << EOF
*~
*.dpkg-new
*.dpkg-old
blkid.tab(|.old)
mtab
# add other files if necessary, depends on your setup...
EOF

Do the initial commit:

git add .
git commit -a -m "initial import"

Set up a script to check in any change made when installing new packages. Put this in /etc/apt and call it something like, git-snapshot-script. Here is the script I use (UPDATED: Jul 11, 2007):

#!/bin/bash
set -e
caller=$(ps axww | mawk '/aptitude|apt-get/ {for (i=5; i<=NF ; i++) printf ("%s ",$i); printf ("\n") }' | head -1)
git-add .

# the || true is to make sure we don't error out because of the set -e
# above
STATUS="$(git status)" || true

if echo $STATUS | grep '\(Changed\|Update\)' > /dev/null ; then
   echo "git-snapshot-script: found changed files"
   echo $STATUS
   git-commit -a -m "snapshot after: $caller"
else
   echo "git-snapshot-script: no changes"
fi
echo "git-snapshot-script: done"

Then tell apt to run this script after it's invoked:

cat >> /etc/apt/apt.conf << EOF
DPkg {
          Post-Invoke {"cd /etc ; ./apt/git-snapshot-script";};
}
EOF

chmod +x /etc/apt/git-snapshot-script

Now, check in the script and the change to apt.conf:

git add .
git commit -a -m "set up apt to track changes with git automatically"

And that should do it.