I recently read Ian Jackson's Debian’s git transition ( via ) and had a reaction :

I would really like to be able to patch and rebuild Ubuntu packages from a git repository with our local changes (re)based on top of upstream git. It would be much better than quilt'ing and debuild'ing .dsc packages (I have non-complimentary opinions on the Debian source package format). This news gives me hope that it'll be possible someday, but especially for Ubuntu I have no idea how soon or how well documented it will be.

(It could even be better than RPMs.)

The subsequent discussion got me to try out dgit , especially since it had an attractive dgit-user(7) manual page that gave very simple directions on how to make a local change to an upstream package. It turns out that things aren't entirely smooth on Ubuntu, but they're workable.

The starting point is 'dgit clone', but on Ubuntu you currently get to use special arguments that aren't necessary on Debian:

dgit clone -d ubuntu dovecot jammy,-security,-updates

(You don't have to do this on a machine running 'jammy' (Ubuntu 22.04); it may be more convenient to do it from another one, perhaps with a more up to date dgit .)

The latest Ubuntu package for something may be in either their <release>-security or their <release>-updates 'suite', so you need both. I think this is equivalent to what 'apt-get source' gets you, but you might want to double check. Once you've gotten the source in a Git repository, you can modify it and commit those modifications as usual, for example through Magit . If you have an existing locally patched version of the package that you did with quilt , you can import all of the quilt patches, either one by one or all at once and then using Magit's selective commits to sort things out .

Having made your modifications, whether tentative or otherwise, you can now automatically modify debian/changelog:

gbp dch --since dgit/dgit/jammy,-security,-updates --local .cslab. --ignore-branch --commit

(You might want to use -S for snapshots when testing modifications and builds, I don't know. Our practice is to use --local to add a local suffix on the upstream package number, so we can keep our packages straight.)

The special bit is the 'dgit/dgit/<whatever you used in dgit clone>', which tells gbp-dch (part of the gbp suite of stuff) where to start the changelog from. Using --commit is optional; what I did was to first run 'gbp dch' without it, then use 'git diff' to inspect the resulting debian/changelog changes, and then 'git restore debian/changelog' and re-run it with a better set of options until eventually I added the '--commit'.

You can then install build-deps (if necessary) and build the binary packages with the dgit-user(7) recommended 'dpkg-buildpackage -uc -b'. Normally I'd say that you absolutely want to build source packages too, but since you have a Git repository with the state frozen that you can rebuild from, I don't think it's necessary here.

(After the build finishes you can admire 'git status' output that will tell you just how many files in your source tree the Debian or Ubuntu package building process modified. One of the nice things about using Git and building from a Git repository is that you can trivially fix them all, rather than the usual set of painful workarounds.)

The dgit-user(7) manual page suggests but doesn't confirm that if you're bold, you can build from a tree with uncommitted changes. Personally, even if I was in the process of developing changes I'd commit them and then make liberal use of rebasing, git-absorb , and so on to keep updating my (committed) changes.

It's not clear to me how to integrate upstream updates (for example, a new Ubuntu update to the Dovecot package) with your local changes. It's possible that ' dgit pull' will automatically rebase your changes, or give you the opportunity to do that. If not, you can always do another 'dgit clone' and then manually import your Git changes as patches .

(A disclaimer: at this point I've only cloned, modified, and built one package, although it's a real one we use. Still, I'm sold; the ability to reset the tree after a build is valuable all by itself, never mind having a better way than quilt to handle making changes.)