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People behind Debian: Mehdi Dogguy, release assistant

December 23, 2010 by Raphaël Hertzog

Mehdi Dogguy
Picture of Mehdi taken by Antoine Madet

Mehdi is a Debian developer for a bit more than a year, and he’s already part of the Debian Release Team. His story is quite typical in that he started there by trying to help while observing the team do its work. That’s a recurrent pattern for people who get co-opted in free software teams.

Read on for more info about the release team, and Mehdi’s opinion on many topics. My questions are in bold, the rest is by Mehdi (except for the additional information that I inserted in italics).

Who are you?

I’m 27 years old. I grew up in Ariana in northern Tunisia, but have been living in Paris, France, since 2002.

I’m a PhD Student at the PPS laboratory where I study synchronous concurrent process calculi.

I became interested in Debian when I saw one of my colleagues, Samuel Mimram (first sponsor and advocate) trying to resolve #440469, which is a bug reported against a program I wrote. We have never been able to resolve it but my intent to contribute was born there. Since then, I started to maintain some packages and help where I can.

What’s your biggest achievement within Debian?

I don’t think I had time to accomplish a lot yet 🙂 I’ve been mostly active in the OCaml team where we designed a tool to compute automatically the dependencies between OCaml packages, called dh-ocaml. This was a joint work with Stéphane Glondu, Sylvain Le Gall and Stefano Zacchiroli. I really appreciated the time spent with them while developing dh-ocaml. Some of the bits included in dh-ocaml have been included upstream in their latest release.

I’ve also tried to give a second life to the Buildd Status Pages because they were (kind of) abandoned. I intend to keep them alive and add new features to them.

If you had a wand and could change one thing in Debian, what would that be?

Make OCaml part of a default Debian installation 😀

But, since I’m not a magician yet, I’d stick to more realistic plans:

  1. A lot of desktop users fear Debian. I think that the Desktop installation offered by Debian today is very user-friendly and we should be able to attract more and more desktop users. Still, there is some work to be done in various places to make it even more attractive. The idea is trying to enhance the usability and integration of various tools together. Each fix could be easy or trivial but the final result would be an improved Desktop experience for our users. Our packaged software run well. So, each person can participate since the most difficult part is to find the broken scenarios. Fixes could be found together with maintainers, upstream or other interested people.

    I’ll try to come up with a plan, a list of things that need polishing or fixes and gather a group of people to work on it. I’d definitely be interested in participating in such a project and I hope that I’ll find other people to help. If the plan is clear enough and has well described objectives and criteria, it could be proposed to the Release Team to consider it as a Release Goal for Wheezy.

  2. NMUs are a great way to make things move forward. But, sometimes, an NMU could break things or have some undesirable effects. For now, NMUers have to manually track the package’s status for some time to be sure that everything is alright. It could be a good idea to be auto-subscribed to the bugs notifications of NMUed packages for some period of time (let’s say for a month) to be aware of any new issues and try to fix them. NMUing a package is not just applying a patch and hitting enter after dput. It’s also about making sure that the changes are correct and that no regressions have been introduced, etc…
  3. Orphaned packages: It could be considered as too strict and not desired, but what about not keeping orphaned and buggy packages in Testing? What about removing them from the archive if they are buggy and still unmaintained for some period? Our ftp archive is growing. It could make sense to do some (more strict) housekeeping. I believe that this question can be raised during the next QA meeting. We should think about what we want to do with those packages before they rot in the archive.

[Raphael Hertzog: I would like to point out that pts-subscribe provided by devscripts makes it easy to temporarily subscribe to bug notifications after an Non-Maintainer Upload (NMU).]

You’re a Debian developer since August 2009 and you’re already an assistant within the Release Management team. How did that happen and what is this about?

In the OCaml team, we have to start a transition each time we upload a new version of the OCaml compiler (actually, for each package). So, some coordination with the Release Team is needed to make the transition happen.

When we are ready to upload a new version of the compiler, we ask the Release Team for permission and wait for their ack. Sometimes, their reply is fast (e.g. if their is no conflicting transition running), but it’s not always the case. While waiting for an ack, I used to check what was happening on debian-release@l.d.o. It made me more and more interested in the activities of the Release Team.

Then (before getting my Debian account), I had the chance to participate in DebConf9 where I met Luk and Phil. It was a good occasion to see more about the tools used by the Release Team. During April 2010, I had some spare time and was able to implement a little tool called Jamie to inspect the relations between transitions. It helps us to quickly see which transitions can run in parallel, or what should wait. And one day (in May 2010, IIRC), I got offered by Adam to join the team.

As members of the Release Team, we have multiple areas to work on:

  1. Taking care of transitions during the development cycle, which means making sure that some set of packages are correctly (re-)built or fixed against a specific (to each transition) set of packages, and finding a way to tell Britney that those packages can migrate and it would be great if she also shared the same opinion. [Raphael Hertzog: britney is the name of the software that controls the content of the Testing distribution.]
  2. Paying attention to what is happening in the archive (uploads, reported RC bugs, etc…). The idea is to try to detect unexpected transitions, blocked packages, make sure that RC bug fixes reach Testing in a reasonable period of time, etc…
  3. During a freeze, making sure that unblock requests and freeze exceptions are not forgotten and try to make the RC bug count decrease.

There are other tasks that I’ll let you discover by joining the game.

Deciding what goes (or not) in the next stable release is a big responsibility and can be incredibly difficult at times. You have to make judgement calls all the time. What are your own criteria?

That’s a very hard to answer question (at least, for me). It really depends on the “case”. I try to follow the criteria that we publish in each release update. Sometimes, an unblock request doesn’t match those criteria and we have to decide what to accept from the set of proposed changes. Generally, new features and non-fixes (read new upstream versions) changes are not the kind of changes that we would accept during the freeze. Some of them could be accepted if they are not intrusive, easy and well defended. When, I’m not sure I try to ask other members of the Release Team to see if they share my opinion or if I missed something important during the review. The key point is to have a clear idea on what’s the benefit of the proposed update, and compare it to the current situation. For example, accepting a new upstream release (even if it fixes some critical bugs) is taking a risk to break other features and that’s why we (usually) ask for a backported fix.

It’s also worth noticing that (most of the time) we don’t decide what goes in, but (more specifically) what version of a given package goes in and try to give to the contributors an idea on what kind of changes are acceptable during the freeze. There are some exceptions though. Most of them are to fix a critical package or feature.

Do you have plans to improve the release process for Debian Wheezy?

We do have plans to improve every bit in Debian. Wheezy will be the best release ever. We just don’t know the details yet 🙂

During our last meeting in Paris last October, the Release Team agreed to organize a meeting after Squeeze’s release to discuss (among other questions) Wheezy’s cycle. But the details of the meeting are not fixed yet (we still have plenty of time to organize it… and other more important tasks to care about). We would like to be able to announce a clear roadmap for Wheezy and enhance our communication with the rest of the project. We certainly want to avoid what happened for Squeeze. Making things a bit more predictable for developers is one of our goals.

Do you think the Constantly Usable Testing project will help?

The original idea by Joey Hess is great because it allows d-i developers to work with a “stable” version of the archive. It allows them to focus on the new features they want to implement or the parts they want to fix (AIUI). It also allows to have constantly available and working installation images.

Then, there is the idea of having a constantly usable Testing for users. The idea seems nice. People tend to like the idea behind CUT because they miss some software disappearing from Testing and because of the long delays for security fixes to reach Testing.

If the Release Team has decided to remove a package from Testing, I think that there must be a reason for that. It either means that the software is broken, has unfixed security holes or was asked for the removal by its maintainer. I think that we should better try to spend some time to fix those packages, instead of throwing a broken version in a new suite. It could be argued that one could add experimental’s version in CUT (or sid’s) but every user is free to cherry-pick packages from the relevant suite when needed while still following Testing as a default branch.

Besides, it’s quite easy to see what was removed recently by checking the archive of debian-testing-changes or by querying UDD. IMO, It would be more useful to provide a better interface of that archive for our users. We could even imagine a program that alerts the user about installed software that got recently removed from Testing, to keep the user constantly aware any issue that could affect his machine. About the security or important updates, one has to recall the existence of Testing-security and testing-proposed-updates that are used specifically to let fixes reach Testing as soon as possible when it’s not possible to go through Unstable. I’m sure that the security team would appreciate some help to deal with security updates for Testing. We also have ways to speed migrate packages from Unstable to Testing.

I have to admit that I’m not convinced yet by the benefits brought by CUT for our users.


Thank you to Mehdi for the time spent answering my questions. I hope you enjoyed reading his answers as I did. Subscribe to my newsletter to get my monthly summary of the Debian/Ubuntu news and to not miss further interviews. You can also follow along on Identi.ca, Twitter and Facebook.

5 reasons why Debian Unstable does not deserve its name

December 20, 2010 by Raphaël Hertzog

Debian Unstable (also known as sid) is one of the 3 distributions that Debian provides (along with Stable and Testing).

It’s not conceived as a product for end-users, instead it’s the place where contributors are uploading newer packages. Daily. Yes that means that Unstable is a quickly moving target and it’s not for everybody. But you can use it and your computer won’t explode.

1. It contains mainly stable versions of the software

Yes, you read it right. Unstable is not full of development versions of the various software. It happens on some software but then it’s usually a conscious decision of the maintainer who believes that this specific version is already better than the previous one.

The packages in sid are supposed to migrate to testing, the place where the next Debian stable release is prepared. So maintainers are advised to only upload stuff that is of release quality, the rest should be uploaded to experimental instead.

2. It doesn’t break badly every other day

Breakages happen but they are not a big deal usually. It has been long time since I could not reboot my computer after an upgrade or since the graphical interface was no longer working. The kind of breakages that you have is that one software stops working, or triggers an annoying bug, or that a few packages are uninstallable.

In most cases, you can save yourself by downgrading to the version available in Testing. Or by finding a work-around in the bug tracking system. Or by not upgrading because you have apt-listbugs installed and you have been warned about the problem.

3. It’s the basis of other distributions

If Debian Unstable was really so bad, it would not be a good basis to build a derivative distribution, isn’t it? But Ubuntu and SiduxAptosid (to name only two) are based on Debian Sid.

4. It’s not inherently less secure than Stable or Testing

High impact security vulnerabilities will usually be quickly fixed in Stable and Unstable. The stable upload is done by the security team while the unstable one is made by the maintainer. Testing will usually get the fix through the package uploaded to Unstable, so testing users get security updates with a delay.

For less serious vulnerabilities, it’s entirely possible that stable does not get any update at all. In that case, unstable/testing users are better served since they will get the fix with the next upstream version anyway.

Of course, it happens that maintainers are busy or that something falls through the cracks, but there are other people watching RC bugs who will fix this if the maintainer doesn’t react at all.

5. I use it on my main computer

And many other people do the same. And you can do the same if you meet the criteria below:

  • you can work on the command-line (enough to downgrade a problematic package, to edit configuration files, etc.);
  • you know how to work with APT and multiple distributions in /etc/apt/sources.list;
  • you are able to read/write English so that you can read/file bug reports when needed;
  • you have another computer connected to the Internet that you can use to lookup documentation (or the bug tracking system, or the support mailing lists) when your usual computer is off-line for a reason that you don’t understand.

If you feel you are not ready for the jump, click here to subscribe to this blog (or here via the RSS feed), I’ll surely teach some of the required skills in future articles.

PS: All that said, if you have a working sid installation, do not upgrade it just before an important presentation, or before a trip. It will always break at the most annoying time. Unless you like to live dangerously, of course.

How Ubuntu builds up on Debian

November 22, 2010 by Raphaël Hertzog

I have been asked how Ubuntu relates to Debian, and how packages flow from one to the other. So here’s my attempt at clarifying the whole picture.

Where do the packages come from?

Most packages are created by Debian contributors and they are uploaded in Debian unstable (or Debian experimental). New packages are reviewed by the Debian ftpmasters before being accepted in the official archive. The packages are held in the NEW queue until the review is over, and the time spent there varies between a few hours and a few months (usually they are processed within one week or two).

Ubuntu imports all the official Debian packages, but they also add some packages of their own. About 7% of the Ubuntu packages are third-party software that have been packaged for Ubuntu but not for Debian.

What are the changes made by Ubuntu?

From all the source packages coming from Debian, 17% have additional changes made by Ubuntu. Many of them are part of the “main” repository, which is actively maintained by Canonical and Ubuntu core developers. The “universe” repository is usually closer to the official Debian packages.

Many of the changes made by Ubuntu are the results of the decisions taken during the Ubuntu Developer Summit in order to reach specific goals: provide a better user interface, offer faster boot times, become a better platform for third-party software developers, offer a good integration with their online services (Launchpad, Ubuntu One), etc. Other changes are simply the result of fixing bugs reported by Ubuntu users.

Note that even non-modified source packages will result in different binary packages for Ubuntu. That’s because Ubuntu has made changes to the build environment. They only support Intel-based computers with a 686-class (or newer) CPU, they enable some compiler options that Debian doesn’t, etc. And all binary packages are modified by a program called pkgbinarymangler.

Ubuntu’s release cycle and the relation with Debian

Ubuntu releases every 6 months (that’s what time based releases is about). Debian has a very different schedule. How does Ubuntu manage to reuse Debian’s work?

Ubuntu imports packages from Debian unstable (even experimental sometimes) to get the newest packages. If the Ubuntu package already has Ubuntu-specific changes, they merge their changes in the updated Debian package. Otherwise the Debian package is simply grabbed and rebuilt in Ubuntu. This works well because Debian unstable is much more usable than the name suggests. And this process only goes on during the first 2 months of the cycle (until the Debian Import Freeze), so there’s plenty of time afterward to fix the biggest problems.

In the third and fourth month, it’s still possible to pick updated packages from Debian but it must be requested by a developer, it won’t be done automatically. At the end of the fourth month, the feature freeze is put in place.

The 2 months left are dedicated to bug fixing and polishing the distribution. There are various sub-freezes that happen in this period, you can check the Natty release schedule as an example. Picking updated packages from Debian is now the exception, it will only be allowed if the update on the Debian side is a bug-fix only release.

Credits: some figures taken from a talk of Lucas Nussbaum, they were collected based on the packages available in the Lucid Lynx release of Ubuntu.

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Understanding Debian’s release process

October 18, 2010 by Raphaël Hertzog

Currently, the main product of the Debian project is its stable release[1]. Those release come out approximately every 18-24 months. This article gives a short overview of the process leading to the next stable release.

Creating a new distribution

Immediately after a stable release, a new distribution is created in the Debian archive. Its initial content is a copy of the (just released) stable distribution. Its codename is decided by the release managers and there’s a tradition of picking a character’s name from the Toy Story movie.

As an example, the “wheezy” distribution will be created once “squeeze” (aka Debian 6.0) is out.

For simplicity there’s a generic name to refer to the distribution used to prepare the next stable release: it’s testing. In the Debian archive, testing is just a symbolic link pointing to the right directory (squeeze currently).

Updating packages, working on release goals

During most of the cycle, developers work on packaging new upstream versions and implementing release goals. They upload their packages in the unstable distribution.

From there packages trickle to the testing distribution once they satisfy some quality checks: they must not have new release-critical bugs, they must have been built on all architectures that were previously supported, they must not break any dependency in testing, and they must have spent at least 10 days in unstable.

This minimal period ensures the package has been tested and gives enough time to users to file bugs if the package is suffering from problems. If the problems are deemed release-critical, they will block the migration of the package to testing.

During this part of the release cycle, the main work of the release team is ensuring that updated packages flow from unstable to testing. It can be a tricky task: package dependencies frequently tie packages together so that they can only migrate to testing together. If only one of the tied packages is not ready (for example if a new revision has been uploaded and has not spent 10 days in unstable yet), then none of them can migrate.

Stabilizing, polishing, fixing release-critical issues

The constant churn of new packages makes it very difficult to build a very polished release. That’s why, at some point, release managers freeze the testing distribution: automatic updates are stopped and they vet every single update made to testing. They have strong requirements, the goal is to only allow updates fixing release critical bugs, or those which are low-risk and bring significant value to the user experience (like new translations, updated documentation, etc.).

During freeze, some packages are also removed because the current upstream version can’t be supported for the lifetime of the stable release.

The freeze tends to slow down the pace of changes in unstable. Many maintainers opt to push new upstream versions in experimental instead so that if they need to update their packages in testing, they can still do it through unstable. This procedure is recommended by the release managers because it means that updates that they unblock have been tested as usual. It’s not the case for updates uploaded directly to testing (through testing-proposed-updates).

This behavior is rather annoying for the bleeding-edge users that use testing or unstable like a rolling release.

Release time

Once release managers are satisfied of the quality of the new distribution, some last minute work is needed, like generating the CD images. In the Debian archive, the release is made official by pointing the “stable” symbolic link to the new distribution (and the “oldstable” one to the previous distribution).

Now it’s party time, the cycle is over, and a new one can start. 🙂

[1] The Constantly Usable Testing project aims to make testing a first-class product like stable—but with a very different update policy.

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