Debian – Page 57

Understand dpkg and don’t get stuck with a maintainer script failure

September 13, 2011 by Raphaël Hertzog

Continuing my series of articles on dpkg’s errors, this time I’ll cover a pretty common one which has several variations:

Setting up acpid (1:2.0.12-1) ...
rm: cannot remove `/etc/rc1.d/K20acpid': No such file or directory
dpkg: error processing acpid (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 acpid

Even if dpkg is failing and outputting the error message, the real problem is not in dpkg but in the installed package (acpid in the example above). As we already learned, a package contains not only files but also “maintainer scripts” that are executed at various points of the installation process (see some useful graphics to understand how they are called, thanks to Margarita Manterola).

In the introductory example it was acpid’s “post-installation script” that failed, and dpkg is only forwarding that failure back to the caller. The maintainer scripts are stored in /var/lib/dpkg/info/. You can thus inspect them and even modify them if you hit a bug and want to work around it (do this only if you understand what you do!).

One common modification is to add “set -x” at the start of the script and to retry the failing operation. That way you can see what’s executed exactly. Here’s what the output could look like after the addition of “set -x” to /var/lib/dpkg/info/acpid.postinst:

$ sudo dpkg --configure acpid
Setting up acpid (1:2.0.12-1) ...
+ dpkg --compare-versions 1:2.0.11-1 lt-nl 1.0.10-3
+ dpkg --compare-versions 1:2.0.11-1 lt-nl 1.0.6-16
+ dpkg --compare-versions 1:2.0.11-1 lt 1.0.6-6
+ rm /etc/rc1.d/K20acpid
rm: cannot remove `/etc/rc1.d/K20acpid': No such file or directory
dpkg: error processing acpid (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 acpid

This output helps you locate the command that is actually failing. Here’s it’s relatively easy since we have an error message from “rm”. And the fix is trivial too, we replace “rm” with “rm -f” so that it doesn’t fail when the file doesn’t exist (this is a fake bug I made up for this article—I just added a failing rm call—but it’s inspired by real bugs I experienced).

Maintainer scripts are supposed to be idempotent: we should be able to execute them several times in a row without bad consequences. It happens from time to time that the maintainer gets this wrong… on the first try it works, so he uploads his package and we discover the problem only later once someone ended up executing the same code twice for some reason.

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My Debian activities in August 2011

September 4, 2011 by Raphaël Hertzog

This is my monthly summary of my Debian related activities. If you’re among the people who made a donation to support my work (91.44 €, thanks everybody!), then you can learn how I spent your money. Otherwise it’s just an interesting status update on my various projects.

Dpkg work

When I came back from Debconf, I merged my implementation of dpkg-source --commit (already presented last month). I continued some work on the hardening build flags but it’s currently stalled waiting on Kees Cook to provide the required documentation to integrate in dpkg-buildflags(1).

Following a discussion held during DebConf, Michael Prokop has been kind enough to setup a git-triggered auto-builder of dpkg (using Jenkins). You can now help us by testing the latest git version. Follow those instructions:

$ wget -O - http://jenkins.grml.org/debian/C525F56752D4A654.asc | sudo apt-key add -
$ sudo sponge /etc/apt/sources.list.d/dpkg-git <<END
deb http://jenkins.grml.org/debian dpkg main
END
$ sudo apt-get update && sudo apt-get upgrade

On the bug fixing side I took care of #640198 (minor man page update), #638291 (a fix to correctly handle hardlinks of conffiles), #637564 (the simplification logic of union dependencies was broken in some cases) and #631494 (interrupting dpkg-source while building a native source package left some temporary files around that should have been cleaned).

WordPress update

I released WordPress 3.2.1 in unstable (after having taken the time to test the updated package on my blog!) and fixed its RC bug (#625773). In the process I discovered a false positive in lintian (I reported it in 637473).

Gnome-shell-timer package

From time to time, I like to use the Pomodoro Technique. That’s why I was an user of timer-applet in GNOME 2. Now with the switch to GNOME 3, I lost this feature. But I recently discovered gnome-shell-timer, a GNOME Shell extension that provides the same features.

I created a Debian package of it and quickly filed some bugs while I was testing it (two usability issues and an encoding problem)

QA Work

During DebConf I met Giovanni Mascellani and he was interested to help the QA team. He started working on the backlog of bugs concerning the Package Tracking System (PTS) and submitted a bunch of patches. I reviewed them and merged them but since they were good, I quickly got lazy and got him added to the QA team so that he can commit his fixes alone. It also helps to build trust when you have had the opportunity to discuss face to face. 🙂

Vacation

That’s not so much compared to usual but to my defense I also took 2 weeks of vacation with my family. But somehow even in vacation I can’t really forget Debian. Here’s my son:

Thanks

See you next month for a new summary of my activities.

People behind Debian: Peter Palfrader, Debian System Administrator

August 18, 2011 by Raphaël Hertzog

You might not know who Peter is because he’s not very visible on Debian mailing lists. He’s very active however and in particular on IRC. He was an admin of the OFTC IRC network at the time Debian switched from Freenode to OFTC. Nowadays he’s a member of the Debian System Administration team who runs all the debian.org servers.

If you went to a Debconf you probably met him since he’s always looking for new signatures of his GPG key. He owns the best connected key in the PGP web of trust. He also wrote caff a popular GPG key signing tool.

Raphael: Who are you?

Peter: I’m Peter Palfrader, also known as weasel. I’m in my early 30s, born and raised in Innsbruck, Austria and am now living and working in Salzburg, Austria. In my copious free time, other than help running Debian’s servers I also help maintaining the Tor project‘s infrastructure.

Away from the computer I enjoy reading fiction (mostly English language Science Fiction and Fantasy), playing board games and going to the movies. Weather permitting, I also occasionally do some cycling.

Raphael: How did you start contributing to Debian?

Peter: I installed my first Debian the week slink came out. That was Debian 2.1 for the youngsters, in early 1999. The one thing I immediately liked about slink was that Debian’s pppd supported RAS authentication which my university’s dial-up system required. No way I’d go back to SuSE 5.3 when I had working Internet with my Debian box. 🙂

During that year I started getting involved in the German language Debian channel on IRCnet which got me in contact with some DDs. Christian Kurz (<shorty>) was working on Debian QA at the time and he asked my help in writing a couple of scripts. Some of that work, debcheck, still produces parts of the qa.d.o website, tho the relevance of that nowadays is probably negligible.

While trying to learn more Perl earlier, I had written a program to produce syntax highlighted HTML for code snippets in various languages. I didn’t really know what I was doing but it kinda worked, and probably still does since I still get mail from users every now and then. I figured that it would be really nice if people could just get my software together with Debian. According to code2html‘s Debian changelog the initial release of the package was done on a weekday at 2:30 in the morning early in 2000, and if my memory serves me correctly, shorty uploaded it shortly afterwards.

I started packaging a couple of other piece of software and in the same year I sent my mail to the debian account managers to register my intent to become a DD. No new developers where being accepted at that time since the DAMs wanted to overhaul the entire process so I wasn’t surprised to not get any immediate reply. Of course what the silence also meant was that the mail had been lost, but I only learned of that later when I took all my courage to ask DAM about the status of application a couple months later. Once that was sorted out I was assigned an AM, did the usual dance, and got my account late in November 2000.

Raphael: Four years ago, the Debian System Administration team was a real bottleneck for the project and personal conflicts made it almost impossible to find solutions. You were eager to help and at some point you got dropped as a new member in that team. Can you share your story and how you managed the transition in the difficult climate at that time?

Peter: Ah, that was quite the surprise for an awful lot of people, me included.

Branden Robinson, who was our DPL for the 2005-2006 term, tried to get some new blood added to DSA who were at the time quite divided. He briefly talked to me on IRC some time in summer 2005, telling me I had come “recommended for a role on the sysadmin team”. In the course of these 15 minutes he outlined some of the issues he thought a new member of DSA would face and asked me if I thought I could help. My reply was cautiously positive, saying that I didn’t want to step on anybody’s toes but maybe I could be of some assistance.

And that was the first and last of it, until some fine November day two years later I got an email from Phil Hands saying “I’ve just added you to the “adm” group, and added you to the debian-admin@d.o alias.” and “welcome on board“. *blink* What!?

My teammates at the time were James Troup (elmo), Phil Hands (fil), Martin ‘Joey’ Schulze and Ryan Murray (neuro).

The old team, while apparently not on good terms with one another, was however still around to do heavy lifting when required. I still remember when on my first or second day on the team two disks failed in the raid5 of ftp-master.debian.org aka ries. Neuro did the reinstall once new disks had arrived at Brown University. I’m sure I’d have been way out of my league had this job fallen to me.

Fortunately my teammates were all willing and able to help me find whatever pieces of information existed that might help me learn how debian.org does its stuff. Unfortunately a lot of it only existed in various heads, or when lucky, in one of the huge mbox archives of the debian-admin alias or list. Anyway, soon I was able to get my hands dirty with upgrading from sarge to etch, which had been released about half a year earlier.

Raphael: I know the DSA team has accomplished a lot over the last few years. Can you share some interesting figures?

Peter: Indeed we have accomplished a lot. In my opinion the most important of these accomplishment is that we’re actually once again a team nowadays. A team where people talk to one another and where nobody should be a SPoF.

Since this year’s debconf we are six people in the admin team: Tollef Fog Heen (Mithrandir) and Faidon Liambotis (paravoid) joined the existing members: Luca Filipozzi, Stephen Gran, Martin Zobel-Helas, and myself. Growing a core team, especially one where membership comes with uid0 on all machines, is not easy and that’s why I’m very glad we managed to actually do this step.

I also think the infrastructure and our workflows have matured well over the last four years.

We now have essential monitoring as a matter of course: Nagios not only checks whether all daemons that should be running are in fact running, but it also monitors hardware health of disks, fans, etc. where possible. We are alerted of outstanding security updates that need to be installed and of changes made to our systems that weren’t then explicitly acked by one of us.

We have set up a centralized configuration system, puppet, for some of our configuration that is the same, or at least similar, on all our machines.

Most, if not all, pieces of software, scripts and helpers that we use on debian.org infrastructure is in publicly accessible git repositories.

We have good communication with other teams in Debian that need our support, like the ftp folks or the buildd people.

As for figures, I don’t think there’s anything spectacular. As of the time of our BoF at this year’s DebConf, we take care of approximately 135 systems, about 100 of them being real iron, the other virtual machines (KVM). They are hosted at over 30 different locations, tho we are trying to cut down on that number, but that’s a long and difficult process.

We don’t really collect a lot of other figures like web hits on www.debian.org or downloads from the ftp archive. The web team might do the former and the latter is pretty much impossible due to the distributed nature of our mirrors, as you well know.

Raphael: The DSA team has a policy of eating its own dog food, i.e. you’re trying to rely only on what’s available in Debian. How does that work out and what are the remaining gaps?

Peter: Mostly Debian, the OS, just meets our needs. Sure, the update frequency is a bit high, we probably wouldn’t mind a longer release cycle. But on the other hand most software is recent enough. And when it’s not, that’s easy to fix with backports. If they aren’t on backports.debian.org already, we’ll just put them there (or ask somebody else to prepare a backport for us) and so everybody else benefits from that work too.

Some things we need just don’t, and probably won’t, exist in Debian. These are mainly proprietary hardware health checks like HP’s tools for their servers, or various vendors’ programs to query their raid controller. HP actually makes packages for their stuff which is very nice, but other things we just put into /usr/local, or if we really need it on a number of machines, package ourselves.

The push to cripple our installers and kernels by removing firmware was quite annoying, since it made installing from the official media next to impossible in some cases. Support for working around these limitations has improved with squeeze so that’s probably ok now.

One of the other problems is that especially on embedded platforms most of the buildd work happens on some variation of development boards, usually due to increased memory and hard disk requirements than the intended market audience. This often implies that the kernel shipped with Debian won’t be usable on our own debian.org machines. This makes keeping up with security and other kernel fixes way more error prone and time intensive. We keep annoying the right people in Debian to add kernel flavors that actually boot on our machines, and things are getting better, so maybe in the future this will no longer be a problem.

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

Peter: One of the things that I think is a bit annoying for admins that maintain machines all over the globe is mirror selection. I shouldn’t have to care where my packages come from, apt-get should just fetch them from a mirror, any mirror, that is close by, fast and recent. I don’t need to know which one it was.

We have deployed geodns for security.debian.org a while ago, and it seems to work quite well for the coarse granularity we desired for that setup, but geodns is an ugly hack (I think it is a layer violation), it might not scale to hundreds or thousands of mirrors, and it doesn’t play well with DNSSEC.

What I’d really like to see is Debian support apt’s mirror method that — I think (and I apologize if I’m wronging somebody) — Michael Vogt implemented recently. The basic idea is that you simply add deb mirror://mirror.debian.org/ or something like that to your sources.list, and apt goes and asks that server for a list of mirrors it should use right now.

The client code exists, but I don’t know how well tested it is. What is missing is the server part. One that gives clients a mirror, or list of mirrors, that are close to them, current, and carry their architecture.

It’s probably not a huge amount of work, but at the same time it’s also not entirely trivial. If I had more time on my hands this is something that I’d try to do. Hopefully somebody will pick it up.

Raphael: What motivates you to continue to contribute year after year?

Peter: It’s fun, mostly. Sure, there are things that need to be done regularly that are boring or become so after a while, but as a sysadmin you tend to do things once or twice and then seek to automate it.

DSA’s users, i.e. DDs, constantly want to play with new services or approaches to make Debian better and often they need our support or help in their endeavors. So that’s a constant flow of interesting challenges.

Another reason is that Debian is simply where some of my friends are. Working on Debian with them is interacting with friends.

I not only use Debian at debian.org. I use it at work, I use it on my own machines, on the servers of the Tor project. When I was with OFTC Debian is what we put on our machines. Being a part of Debian is one way to ensure what Debian releases is actually usable to me, professionally and with other projects.

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

Peter: That’s a hard one. There are certainly people who I respect greatly for their technical or other contributions to Debian, but I don’t want to single anybody out in particular. I think we all, everyone who ever contributed to Debian with code, support or a bug report, can be very proud of what we are producing — one of the best operating systems out there.

Thank you to Peter 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.

People behind Debian: Margarita Manterola, Debian Women member

August 7, 2011 by Raphaël Hertzog

When I think about Margarita, I always remember her as a friendly and welcoming person. Like most of the Debian Women members by the way. But she likes to spread some love and organized a Debian Appreciation Day for example.

I think I met her in real life for the first time at Debconf 6 in Oaxtepec (Mexico). She deeply cares about Debian in general. She has proven it multiple times with her DPL candidacy and by giving talks like Making Debian rule again.

One last thing, Debconf11 is just over and you will see that Debconf4 has had a big influence on Marga. My advice is simple: next time there’s a Debconf on your continent, make sure to take a few days off and come to meet us! It really gives another picture of the Debian community. Now let’s proceed with the interview.

Raphael: Who are you?

Margarita: I’m Margarita Manterola, a Software Developer from Argentina. I work developing software in Python in a Debian-friendly company during the day, and teach programming at a local university during the evenings.

I’m married to Maximiliano Curia who is also a Debian Developer, most of our Free Software work has been done together.

I only maintain a handful of packages in Debian, I’m more interested in fixing bugs than in packaging new software.

I’ve also been a part of the organizing team of many of the previous Debian Conferences. One of the biggest commitments and the biggest success of my participation in Debian was being part of the organizing team of DebConf8, in Argentina.

Raphael: How did you start contributing to Debian?

Margarita: I started using Debian around 2000. Soon after we had learned the grips of general GNU/Linux usage, Maxy and I started giving an introductory course at our local university, and became quite involved with the local LUG.

At some point in 2002/2003 I became a “Debian Bug Reporter”: most of my friends would report bugs to me, and I would then write them in the proper form to the BTS. I would also be very attentive about reporting any bugs that I might encounter myself trying to create good bug reports.

The turning point in my participation in Debian was DebConf4 in Porto Alegre, Brazil. Being so close to Argentina meant that we felt specially invited to be there, and Maxy and I decided to go to DebConf for our honeymoon. We didn’t really know much about DebConf dynamics, but we were really eager to learn more about Debian and become more involved.

What happened was that meeting with DDs from all over the world transformed our lives, we became part of the “Debian family” and wanted to be more and more involved. Soon after that we both started maintaining packages and not long after that, applied to become Developers.

The Debian Women project also meant a lot to me. I felt encouraged all along the way, encouraged to learn, to ask questions and to lose the fear of making mistakes.

I became a Debian Developer on November 2005. Since then, Debian has always been one of the most important things I do in my life.

Raphael There was a Debian Women BoF during debconf. What are the plans for Debian Women in the upcoming months?

Margarita: I was not there in person, but thanks to the awesome work of the video team, and of Christian Perrier’s typing efforts when something failed, I was able to experience much of what was discussed. 🙂

One of the many points that came up during the BOF is that many people “Want to help” but don’t know where to start or how to go about it. It’s a challenge for the Debian Women project to find a way to allow these people to become involved in Debian through “Mini projects” or something like that.

Another of the subjects that was brought up was the Debian Women mentoring project, which has been going on for quite a while now, but lacks enough publicity. So, we need to reach more people about it, and maybe also improve it with some templates, similar to the New Maintainer templates, so that mentees that don’t know where to start have some sort of general path to follow.

Raphael: You created very useful diagrams documenting how package maintainer scripts are invoked by dpkg. How did you do it and was that a useful experience?

Margarita: I did those diagrams to be able to answer one of the questions in the NM templates, regarding the order of the maintainer script execution.

Answering the question in text was basically copying and pasting the part of the Debian Policy that explained it, which wasn’t really too clear for me, so I decided to go and make a diagram of it, so that I could really understand it.

I did it by the best of all debugging techniques: adding prints to each of the maintainer scripts, and testing them in all the different orders that I could think of.

It was a useful experience at the time, because I learned a lot of how maintainers scripts work. I didn’t expect the diagrams to become so famous, though, I only did them to answer one NM question, that I assumed most other people had already answered before 🙂

Raphael: You participated in a DPL election. This is a big commitment to make. What were your motivations?

Margarita: As I said, I was part of the organizing team of DebConf8, in Argentina. Which was quite a success, a lot of people enjoyed it and praised the good work that had been done by the local team.

During said DebConf8, I had a dream (it was almost a nightmare, actually): I woke up and just like that, I was the DPL. I spoke to some people about this dream and to my complete surprise many said that I should actually do it.

After giving that possibility a year and a half of thoughts, during the 2010 campaign I was talked into participating myself as a candidate, and it was a very interesting experience. However, I’m very glad that Zack got elected and not me, I think he makes a much better DPL that I would have made.

Raphael: What’s the biggest problem of Debian?

Margarita: I think the main problem that we have is our communication, both inside the project and outside the project. Most of us are very technical people, our skills lay in the technical part of Debian (preparing packages, fixing bugs, writing software, administering systems) not in the social part. And thus, we lack a general empathy that is quite needed when interacting with people from all over the world.

Raphael: Do you have wishes for Debian Wheezy?

Margarita: Not particularly. I do want it to be a great release with good quality, stable software. I would also like to keep making Debian more and more “universal” with each release, making it more user friendly, more accessible, and more robust than any other previous release.

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

Margarita: I admire a lot of people in Debian. There’s a lot of people that contribute a lot of time to Debian, amounts of time that I can’t begin to understand how they can afford.

I admire Stefano Zacchiroli, our current project leader. And Steve McIntyre, the project leader before him. Also Bdale Garbee, who’s also been a DPL in the past. Making this list I realize that Debian has been blessed by quite a number of great leaders in the past.

I admire Holger Levsen, for his contributions to the DebConf video team, that have made it possible year after year for the whole project to participate in DebConf remotely.

I admire Steve Langasek and Andreas Barth (etch is still my favourite release). I admire Christian Perrier for his work on internationalization. I admire Joerg Jaspert for the incredible amounts of time that he puts into Debian.

And actually, I could go on admiring people all night long. I admire so many people that this interview could become a very boring list of names. I guess it’s better to leave it at saying that Debian is lucky to have quite a lot of excellent hackers around.

Thank you to Marga for the time spent answering my questions. I hope you enjoyed reading her 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.