Tente algo assim:
# exit on failure
set -e
package=php5-fpm
mkdir $package
cd $package
# you could also get the file from a package mirror if you have
# an older version of apt-get that doesn't support 'download'
# or if you would like more control over what package version
# you are downloading.
# (e.g. http://archive.ubuntu.com/ubuntu/pool/main/)
apt-get download $package
# deb package files are ar archives
ar vx ${package}*.deb
# containing some compressed tar archives
tar xzf data.tar.gz
# now you have the files
# you can get diffs for all of the files in etc if you would like
find etc -type f |
while read file ; do
diff $file /$file
done
Como sugerido por outros, definitivamente coloque seus arquivos de configuração sob controle de revisão. Dessa forma, você pode ver exatamente o que mudou e quando mudou.