testing

People behind Debian: Steve Langasek, release wizard

May 6, 2011 by Raphaël Hertzog

Steve Langasek has been contributing to Debian for more than a decade. He was a release manager for sarge and etch, and like many former release managers, he’s still involved in the Debian release team although as a release wizard (i.e. more of an advisory role than a day-to-day contributor). Oh, and he did the same with Ubuntu: on the picture on the left, he just announced the release of Ubuntu 10.04 from his Debian-branded laptop. 😉

He has also been maintaining PAM in Debian for as long as can I remember and does a great job at that. He’s very knowledgeable and fully deserves his place within the Debian Technical Committee. I’m glad he still has the time to participate on several important Debian mailing lists because his contributions are always very useful.

I’m sure you’ll notice this just by reading his answers below. My questions are in bold, the rest is by Steve.

Who are you?

I’m 32 years old, have been running Linux since my first year in college back in ’96, and have been a Debian developer now for ten years. Along the way I’ve been involved in maintaining a variety of server packages, worked on the Alpha port for a while, did a stint as a release manager for a couple of years, and serve on the technical committee.

This year I’m also celebrating my ten year anniversary with my lovely wife Patty, who many know as an erstwhile front-desk volunteer at DebConf. God only knows why she puts up with my late-night hacking!

These days in my day job I’m a manager on the Ubuntu Platform team at Canonical, working to help make Ubuntu a daughter distribution that the Debian community can be proud of.

What’s your biggest achievement within Debian or Ubuntu?

There’s no doubt that my biggest achievement in Debian has been overseeing the release of two Debian releases as release manager.

On the other hand, the scope of a release is so huge, and it represents the output of so many developers working together, that it would be arrogant to claim the release itself as an achievement of my own. Also, sarge and etch have long since been rotated off of the mirrors so no one cares about them anymore. 😉 For a more personal and lasting contribution in the distro itself, I’m very proud of writing pam-auth-update. It’s a small piece of code, but one that Debian was missing for a long time – it’s made a big difference to PAM module integration in packages!

What are your plans for Debian Wheezy?

My top priority for this cycle is to see multiarch through. We’re still not far enough along in Debian for most developers to see any difference… and once we are, the first thing people are going to see is a fair bit of breakage when we start breaking a lot of assumptions about paths that have been hard-coded upstream. But I’m still excited by the progress that is being made here. We should be able to ship wheezy without any ia32-libs package. We might even be able to get rid of all the biarch library packages, including those used by the toolchain itself. 54 packages in testing build-depend on gcc-multilib right now, in order to build 32-bit code to ship in the amd64 package; a bunch of those should go away with absolutely no reduction in functionality, saving us a bit of space in the archive and saving the maintainers a lot of complexity in their packages, while at the same time giving us much better support for cross-compilation than we’ve ever had before.

It’s a tall order, certainly, but the pieces are falling into place one by one.

My second priority is to get a policy in Debian around packages integrating upstart jobs. It would of course benefit Ubuntu to have many packages back in sync with Debian, but if all we wanted was to sync with Debian, we could mostly just make debhelper ignore upstart jobs in Debian, prefer them in Ubuntu, and call it good. I’m interested in making sure Debian also gets the benefits of being able to use upstart, because as Linux has become increasingly asynchronous (doing more in parallel at start up), the traditional sysvinit has not been able to keep up. There are all kinds of bugs now related to network startup, for instance, that we don’t have a good answer for in a sysvinit model but that we can fix with an event-based system.

Upstart has been around for a while now, but we’ve been slow to integrate it into Debian because it only works on Linux. It would be a shame if right after the first Debian GNU/kFreeBSD technology preview, packages all stopped working on kFreeBSD because they started to assume the availability of upstart! Unfortunately, having been so cautious we now have systemd on the scene, which not only doesn’t support non-Linux but seems to be in the process of trying to gobble up other, non-Linux-specific components of the desktop stack. So I have to wonder what the future holds for the free desktop on non-Linux kernels.

If you could spend all your time on Debian, what would you work on?

Well, based on my previous experiences when I did spend all my time on Debian, I think the answer here is QA / release work. 🙂 Otherwise, I don’t know. My hands are full enough now with multiarch that it’s hard for me to see what the Next Thing would be.

You’re a member of the technical committee. In the interview of Bdale Garbee, I have argued that it’s not working well. What’s your point of view on this topic?

Well, I feel a constant low level guilt about my own poor level of activity in the TC; but that doesn’t translate into a belief that the system is broken. This is, after all, the decision making body of last resort for technical disputes in Debian, and as such it should really be used sparingly. And if a reputation for glacial deliberation means more developers work out their disputes on their own rather than asking the TC to step in, I think that’s actually a healthy thing!

I do still wish we were more effective at resolving those issues that do come our way, but there’s no silver bullet for this. Though the funny thing is, I’ve noticed that the majority of issues that get referred to the TC nowadays never even need us to make a decision; a short conversation with the disputants is often enough to get them to come to an agreement.

What’s the biggest problem of Debian?

By and large, I think Debian is still doing a great job at what it’s best at — delivering a rock-solid distribution that users can rely on. If I would highlight one problem in Debian, though, it would be that I think we’re becoming less innovative as time goes on. Part of that comes from being such a large project that we’re bound to be more conservative as an institution; but even though the three pet Debian projects of mine that I mentioned above are fairly innovative (multiarch, pam-auth-update, upstart), each of these has landed first in Ubuntu rather than in Debian. Always with a clear intent of pushing back up into Debian, of course, but it just wasn’t possible to do this work within Debian for the first cut without much longer delays.

I worry that if Debian is no longer the place to try new things, that we’re going to miss out on attracting contributions from the folks who are inspired to make Free Software better – and not simply to make it stable.

I’m not sure how to address this, though. Maybe improved conversations with derivatives such as (but not limited to) Ubuntu, about what crack of the day is being tried where and how that can be integrated into Debian once it’s proven to work? I don’t think that team-based maintenance or low-threshold NMUs do anything to address this, though, as the kinds of innovation that matter most are ones that require discussion and consensus-finding — not just routing around inactive maintainers.

Do you have wishes for Debian Wheezy?

Well, I’d like to see the armhf port get on its feet and become an official port. Over the lifetime of the arm and armel ports, the state of the art on ARM has changed quite a bit; it would be great to see Debian taking advantage of this richer platform, to let people make better use of their hardware via Debian.

As a former release manager, you’re now a “release wizard”. I guess you have seen it on debian-devel, there are proposals to not freeze testing and to use another distribution starting as a snapshot of testing to finalize the new stable release. According to your experience, what needs to happen to make this possible?

Frankly, I’ve stayed out of that discussion because I don’t think what’s being asked for is possible. I think proponents of a freezeless release have seriously underestimated the amount of work required on the part of the release team to wrangle testing into a releasable product, and that anything that makes propagation of fixes into the pending release more time consuming will make Debian worse on the whole, not better.

If people really want to avoid long freezes for the Debian release, the best way they can help this happen is by making Debian more releasable on an ongoing basis, by helping to hold our packages to our shared standards for quality (i.e., by fixing RC bugs!). The biggest factor in long freezes for Debian is the slow rate at which we bring the RC bug count down during the freeze. Back in the sarge, etch days we used to have really great bug squashing parties that would get people together on weekends to hack through RC bugs by the dozens. I don’t see that happening as much anymore. I’d really like us to get back to that, but my few attempts at this so far since retiring as release manager have led me to think I’m really terrible at organizing parties of any kind. 🙂

On the other side, as seen at http://bugs.debian.org/release-critical/, the RC bug count for testing at the beginning of the release cycle keeps getting higher and higher. I’d love to know why that is so we can address it. I know we’ve gotten better at detecting some classes of RC bugs; that’s part of it, but I don’t think it explains the whole trend.

Is there someone in Debian that you admire for their contributions?

Wow, what kind of arrogant jerk would I be if I didn’t admire anyone in Debian for their contributions? Debian is and always has been an amazing community of top-notch developers; there are certainly too many I admire to list them all here. Joey Hess certainly makes the list, for his longstanding example of code speaking louder than words and for his ability to get to the heart of common problems and come up with elegant solutions. So does Russ Allbery, who by all accounts had his ability to feel anger in response to email burned out of him at a young age in a flame-related accident on Usenet. 😉 The list goes on, but here I think I have to follow Joey’s example and cut the words short.

Thank you to Steve 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 ~~Sidux~~Aptosid (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.

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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Can Debian offer a Constantly Usable Testing distribution?

October 4, 2010 by Raphaël Hertzog

Debian’s “testing” distribution is where Debian developers prepare the next stable distribution. While this is still its main purpose, many users have adopted this version of Debian because it offers them a good trade-off between stability and freshness. But there are downsides to using this distribution and the “Constantly Usable Testing” (CUT) project aims to resolve those. This article will present the project and the challenges involved to make it happen.

About Debian unstable & testing

Debian unstable is the distribution where developers upload new versions of their packages. It happens frequently that some packages are not installable due to changes in other packages or due to transitions not yet completed.

Debian testing, on the contrary, is managed by a tool that ensures the consistency of the whole distribution: it picks updates from unstable only if the package has been enough tested (10 days usually), if it’s free of new release-critical bugs, if it’s available on all supported architectures, and if it doesn’t break any other package already present in testing. The Release Team (RT) controls this tool and provide “hints” to help it find a set of packages that can flow from unstable to testing.

Those rules also ensure that the packages that flow into testing are reasonably free of show-stopper bugs (like a system that doesn’t boot, or X that doesn’t work at all). This makes it very attractive to users who like to regularly get new upstream versions of their software without dealing with the biggest problems associated to them. This is all very attractive, yet several Debian developers advise people to not use testing. Why is that?

Known problems with testing

Disappearing software

The release team use this distribution to prepare the next stable release and from time to time they remove packages from it. Either because it’s needed to ensure that other packages can migrate from unstable to testing, or because they have long-standing release-critical bugs without progress towards a resolution. It also happens that they remove packages on request of the maintainers because they believe that the current version of the software cannot be supported (security-wise) for 2 years or more. The security team also regularly issues such requests.

Long delays for security and important fixes

Despite the 10-day delay in unstable, there are always some annoying bugs (and security bugs are no exceptions) that are only discovered when the package already has migrated to testing. The maintainer might be quick to upload a fixed package in unstable, and might even raise the urgency to allow the package to migrate sooner, but if the packages gets entangled in a large ongoing transition, it will not migrate before the transition is completed. Sometimes it can take weeks for that to happen.

This delay can be avoided by doing direct uploads to testing (through testing-proposed-updates) but this is almost never used, except during a freeze, where targeted bugfixes are the norm.

Not always installable

With testing evolving daily, updates sometimes break the last installation images available (in particular netboot images that get everything from the network). The debian-installer (d-i) packages are usually quickly fixed but they don’t move to testing automatically because the new combination of d-i packages has not necessarily been validated yet. Colin Watson sums up the problem:

Getting new installer code into testing takes too long, and problems remain unfixed in testing for too long. […] The problem with d-i development at the moment is more that we’re very slow at producing new d-i *releases*. […] Your choices right now are to work with stable (too old), testing (would be nice except for the way sometimes it breaks and then it tends to take a week to fix anything), unstable (breaks all the time).

CUT’s history

CUT finds its root in an old proposal by Joey Hess: it introduces the idea that the stable release is not Debian’s sole product and that testing could become — with some work — a suitable choice for end-users. Nobody took on that work and there was no visible progress in the last 3 years.

But recently Joey brought up CUT again on the debian-devel mailing list and Stefano Zacchiroli (the Debian project leader) challenged him to setup a BoF on CUT for Debconf10. It turned out to be one of the most heavily attended BoF (video recording is here), there is clearly a lot of interest in the topic.

There’s now a dedicated wiki and an Alioth project with a mailing list. The rest of this article tries to summarize the various options discussed and how they’re supposed to address the problems identified.

The ideas behind CUT

Among all the ideas, there are two main approaches that have been discussed. The first is to regularly snapshot testing at points where it is known to work reasonably well (those snapshots would be named “cut”). The second is to build an improved testing distribution tailored to the needs of users who want a working distribution with daily updates, its name would be “rolling”.

Regular snapshots of testing

There’s general agreement that regular snapshots of testing are required: it’s the only way to ensure that the generated installation media will continue to work until the next snapshot. If tests of the snapshot do not reveal any major problem, then it becomes the latest “cut”. For clarity, the official codename would be date based: e.g. “cut-2010-09” would be the cut taken during September 2010.

While the frequency has not been fixed yet, the goal is clearly to be on the aggressive side: at the very least every 6 months, but every month has been suggested as well. In order to reach a decision, many aspects have to be balanced.

One of them (and possibly the most important) is the security support. Given that the security team is already overworked, it’s difficult to put more work on their shoulders by declaring that cuts will be supported like any stable release. No official security support sounds bad but it’s not necessarily so problematic as one might imagine. Testing’s security record is generally better than stable’s one (see the security tracker) because fixes flow in naturally with new upstream versions. Stable still get fixes for very important security issues sooner than testing, but on the whole there are less known security-related problems in testing than in stable.

Since it’s only a question of time until the fixed version comes naturally from upstream, more frequent cut releases means that users get security fixes sooner. But Stefan Fritsch, who used to be involved in the Debian testing security team, has also experienced the downside for anyone who tries to contribute security updates:

The updates to testing-security usually stay useful only for a few weeks, until a fixed version migrates from unstable. In stable, the updates stay around for a few years, which gives a higher motivation to spend time on preparing them.

So if it’s difficult to form a dedicated security team, the work of providing security updates comes back to the package maintainer. They are usually quite quick to upload fixed packages in unstable but tend to not monitor whether the packages migrate to testing. They can’t be blamed because testing was created to prepare the next stable release and there is thus no urgency to get the fix in as long as it makes it before the release.

CUT can help in this regard precisely because it changes this assumption: there will be users of the testing packages and they deserve to get security fixes much like the stable users.

Another aspect to consider when picking a release frequency is the amount of associated work that comes with any official release: testing upgrades from the previous version, writing release notes and preparing installation images. It seems difficult to do this every month. With this frequency it’s also impossible to have a new major kernel release for each cut (since they tend to come out only every 2 to 3 months) and the new hardware support that it brings is something worthwhile to many users.

In summary, regular snapshots address the “not always installable” problem and changes the perception of maintainers towards testing, so that hopefully they care more of security updates in that distribution (and in cuts). But they do not solve the problem of disappearing packages. Something else is needed to fix that problem.

A new “rolling” distribution?

Lucas Nussbaum pointed out that regular snapshots of Debian is not really a new concept:

How would this differentiate from other distributions doing 6-month release cycles, and in particular Ubuntu, which can already be seen as Debian snapshots (+ added value)?

In Lucas’s eyes, CUT becomes interesting if it can provide a rolling distribution (like testing) with a “constant flux of new upstream releases”. For him, that would be “something quite unique in the Free Software world”. The snapshots would be used as starting point for the initial installation, but the installed system would point to the rolling distribution and users would then upgrade as often as they want. In this scenario, security support for the snapshots is not so important, what matters is the state of the rolling distribution.

If testing were used as the rolling distribution, the problem of “disappearing packages” would not be fixed. That’s why there have been discussions of introducing a new distribution named “rolling” that would work like testing but with adapted rules, and the cuts would then be snapshots of rolling instead of testing.

The basic proposal is to make a copy of testing and to re-add the packages which have been removed because they are not suited for a long term release while they are perfectly acceptable for a constantly updated release (the most recent example being Chromium).

Then it’s possible to go one step further: during freeze, testing is no longer automatically updated which makes it inappropriate to feed the rolling distribution. That’s why rolling would be reconfigured to grab updates from unstable (but using the same rules than testing).

Given the frequent releases, it’s likely that only a subset of architectures would be officially supported. This is not a real problem because the users who want bleeding edge software tends to be desktop users on mainly i386/amd64 (and maybe armel for tablets and similar mobile products). This choice — if made — opens up the door to even more possibilities: if rolling is configured exactly like testing but with only a subset of the architectures, it’s likely that some packages migrate to rolling before testing when non-mainstream architectures are lagging in terms of auto-building (or have toolchain problems).

While being ahead of testing can be positive for the users, it’s also problematic on several levels. First, managing rolling becomes much more complicated because the transition management work done by the release team can’t be reused as-is. Then it introduces competition between both distributions which can make it more difficult to get a stable release out, for example if maintainers stop caring of the migration to testing once the migration to rolling has been completed.

The rolling distribution is certainly a good idea but the rules governing it must be designed to avoid any conflict with the process of releasing a stable distribution. Lastly, the mere existence of rolling would finally fix the marketing problem plaguing testing: the name “rolling” does not suggest that the software is not yet ready for prime time.

Conclusion

Whether CUT will be implemented remains to be seen, but it’s off for a good start: ftpmaster Joerg Jaspert said that the new archive server can cope with a new distribution, and there’s now a proposal shaping up. The project might start quickly: there is already an implementation plan for the snapshot side of the project. The rolling distribution can always be introduced later, once it is ready. Both approaches can complement each other and provide something useful to different kind of users.

The global proposal is certainly appealing: it would address the concerns of obsolescence of Debian’s stable release by making intermediary releases. Anyone needing something more recent for hardware support can start by installing a cut and follow the subsequent releases until the next stable version. And users who always want the latest version of every software could use rolling after having installed a cut.

From a user point of view, there are similarities with the mix of usual and long term releases of Ubuntu. But from the development side, the process followed would be quite different, and the constraints imposed by having a constantly usable distribution are stronger: any wide-scale change must be designed in a way that it can happen progressively in a transparent manner for the user.

This article was first published in Linux Weekly News. If you want to see more articles like this, join Flattr and click on the flattr button below every article that you like.