ubuntu-dpkg-downgrade.sh

#!/bin/bash -e

# This script reads a dpkg.log fragment, identifies all of the
# packages upgraded in it, finds and downloads the pre-upgrade
# versions of those packages from Launchpad, and installs them,
# downgrading the system to approximately the state it was in before
# the packages were upgraded.
#
# To use it, copy the section of /var/log/dpkg.log containing the
# upgrade you want to undo into a new file, remove the lines
# corresponding to packages that you _don't_ want to downgrade, and
# then feed the rest into this script either on stdin or by specifying
# the log file name with `--log-file`. You need to either run the
# script as root or specify `--package-dir` to write the downloaded
# packages into a directory you have write access to and
# `--download-only` to download without running `apt-get install` on
# the package files (since you can't do that if you're not root). If
# you do the latter then you can run `sudo apt-get install` afterward,
# specifying the paths to the downloaded deb files. Note that
# `apt-get` won't recognize them as files to be installed unless
# there's at least one slash in their names, so if you're in the same
# directory as the files prefix their names with "./".
#
# Run the script with `--help` for more usage information or just read
# the usage message below.
#
# This is especially useful if you are running a pre-release version
# of Ubuntu, because when they release new versions of prerelease
# packages they delete the old ones from the release repositories, so
# you can't just use apt or apt-get to download and install the old
# version. This script's "secret sauce" is fetching the old versions
# from Launchpad instead of relying on them being in the apt
# repository.
#
# N.B. I don't know if old package builds that aren't actually in a
# final release stay in Launchpad forever or eventually get reaped,
# and if the latter than how long they are saved before being reaped.
# Therefore, it's possible that depending on how long after an upgrade
# you run the script, it won't be able to fetch all the old packages
# to downgrade.
#
# This script was written by Jonathan Kamens <jik@kamens.us>. I
# release it into the public domain. Feel free to do whatever you want
# with it.

whoami="$(basename "$0")"
pkg_dir="/var/cache/apt/archives"
usage="Usage: $whoami [--help] [--download-only] [--package-dir directory]
        [--force] [--log-file dpkg-log]

    --download-only          Download packages without installing them
    --package-dir directory  Store packages in specified directory
                             (default $pkg_dir)
    --force                  Install packages even if some can't be downloaded
    --log-file dpkg-log      Read specified log file instead of stdin"
launchpad_base="https://launchpad.net/ubuntu/+archive/primary/+files"
download_only=false
force=false
log_file=

while [ -n "$1" ]; do
    case "$1" in
        --help) echo "$usage"; exit ;;
        --download-only) shift; download_only=true ;;
        --package-dir*)
            pkg_dir="$2"
            shift; shift
            if [ ! -d "$pkg_dir" ]; then
                echo "'$pkg_dir' is not a directory" 1>&2
                echo "$usage" 1>&2
                exit 1
            fi
            ;;
        --force) shift; force=true ;;
        --log-file)
            log_file="$2"
            shift; shift
            if [ ! -f "$log_file" ]; then
                echo "'$log_file' is not a regular file" 1>&2
                echo "$usage" 1>&2
                exit 1
            fi
            ;;
        *)
            echo "Unrecognized command-line argument '$1'" 1>&2
            echo "$usage" 1>&2
            exit 1
            ;;
    esac
done

if touch $pkg_dir/writable.$$ 2>/dev/null; then
    rm -f $pkg_dir/writable.$$
else
    echo "Can't write to '$pkg_dir'" 1>&2
    exit 1
fi

to_install=""

while read log_line; do
    set $log_line
    shift # date
    shift # time
    if [ "$1" != "upgrade" ]; then
        continue
    fi
    shift # action
    pkg_name=${1%%:*}
    arch=${1##*:}
    shift # pkg_name:arch
    old_version=${1##*:}
    deb_name="${pkg_name}_${old_version}_${arch}.deb"
    if [ -f "$pkg_dir/$deb_name" ]; then
        echo "Already have $deb_name"
    else
        if ! curl --location --silent --output "$pkg_dir/$deb_name" \
             "$launchpad_base/$deb_name"; then
            echo "Failed to download $deb_name" 1>&2
            if ! $force; then
                exit 1
            fi
            continue
        else
            echo "Downloaded $deb_name"
        fi
    fi
    to_install="$to_install $pkg_dir/$deb_name"
done < <(cat $log_file)

if ! $download_only; then
    echo "Installing..."
    apt-get install $to_install
fi