Documentation – Page 4

How to start contributing to Debian?

June 30, 2011 by Raphaël Hertzog

I often get requests of persons who would like to contribute to Debian but who don’t know where to start. Let’s try to answer this question properly so that I can give out this URL the next time that I am asked.

The Debian website has a page explaining how to help Debian. While it provides no less than 10 suggestions in a daunting text-only list, it’s difficult to know what to do next once you picked up something that you could do.

I will try to fix this by providing concrete information for each cases in upcoming articles but in the mean time I propose you another approach to start with. Before answering your question (“what can I do for Debian”), we need to know some information about you.

What motivates you?

You’re a volunteer, you’re not doing stuff for Debian because someone told you so. You must have some intrinsic motivation and the ultimate motivation is usually that you’re enjoying what you’re doing.

So what are you enjoying and/or what are your motivations ?

Is there something that you would like to learn? A new programming language? Packaging? Coding? System administration? A specific software?
Do you want to interact with smart people?
Do you like to help users?
Do you like to fix software just so that it works for you?
Do you like to build something remarkable and useful for millions of people?

On the opposite, make sure to know what you hate and what you want to stay far away from. Maybe you dislike a programming language so much that you don’t want to be involved in a project where you would have to use it, etc.

Write down the answers to the questions, you might need them later when you’ll ask other Debian contributors how you can help.

What are your skills?

If you’re not interested in learning new skills, then you must obviously select a task where your current skills are sufficient. Again make a list of your skills and in particular of skills that you’d like to practice! Here’s a non-exhaustive list of skills to consider:

What languages are you fluent with? Are you confident to write documentation or translate documentation in those languages?
Are you a programmer? If yes, which languages do you know?
Can you diagnose problems? Can you debug problems with strace and/or gdb?
Can you triage bugs?
Do you know some Debian packaging?
Are you an artist and/or a web designer?
Do you know how to work with VCS (subversion, git, bzr, …)?

How much time can you spend on Debian?

This is the last important information that you need to communicate whenever you’re asking someone else what you could do for Debian. There’s no point giving you a big task if you can only spend 30 minutes every week. On the opposite if you can work on Debian full time during a week (because you’re between 2 contracts or because you’re in vacation), it’s equally important to know.

In general contributing to Debian requires time, you should be ready to spend at least several hours per week and possibly more at the start while you’re learning everything.

Find something to do

At this point you have a generic idea of what you’d like to do but you’re still missing a concrete objective. Let’s try to find one, we’ll explore several ways to do this.

Scratch your itch

The best objectives are those that satisfy your own needs. Here are some examples:

Did you notice a missing feature? Try to implement it.
Have you been annoyed by a bug? Try to fix it.
Did you lose too much time on something because there was no documentation? Write the missing documentation and submit it where appropriate.
File bug reports for the things that you can’t fix yourself. Even wishlist bug reports for new features.
Do you use software that are not packaged for Debian? Create the package(s) and maintain it/them.
Do you need a newer version of a package compared to what’s in Debian unstable? Contact the maintainer and propose your help to update the package.
Do you need a newer version of a package compared to what’s in Debian stable? Contact the maintainer and propose your help to create a backport.

If you’re a good Debian citizen, you have already filed bugs for issues that bugged you. Then you can browse http://bugs.debian.org/from:hertzog@debian.org to find out some ideas of stuff to do (obviously replace hertzog@debian.org by your own email address).

Join a team

If you don’t have a specific itch to scratch, you might want to focus your work on a specific team. Head over to wiki.debian.org/Teams and browse the list of teams.

You’ll surely find one that works in an area that you like. If you select a packaging team, pick one that works on packages that you’re actually using.

Some of the teams have instructions for newcomers, follow them when that is the case. Otherwise join the mailing list and the IRC channel, and get a feel of how the team works. See if it suits you, you can follow several teams at the same time and pick the one that you prefer after a few days/weeks.

Once you have lurked a bit, if you still don’t know how you could help, then just ask on the mailing list. Include all the answers you have collected to the 3 questions on your motivations, your skills and your time available.

Focus on a specific package

You can concentrate your work on a specific package even if you’re in a team, it’s often a good idea. But I list it separately because not all packages are team maintained and you might want to help maintain a package where there’s a single maintainer currently. I leave it up to you to find a way to select a package that interests you…

Then head over to the package tracking system: http://packages.qa.debian.org/dpkg (replace dpkg by the name of the package that interests you)

Fill in the form in the bottom-left corner with your email and select “opts” in the drop-down list, then click “go”. You get a new form where you can select the information that you’ll receive, I recommend you to keep everything except “upload-binary” and to validate the form.

From now on, you get the same mails than the maintainer (and a bit more actually), and it’s a good idea to inform the maintainer that you subscribed and that you’re going to help a bit. Maybe he’s willing to grant you commit rights immediately, maybe he will ask you to send patches for a start. The important thing is to create a good relationship. In any case (even if you did not get any answer from the maintainer), you should be free to help triage existing bugs and to help deal with the flow of incoming bugs (including forwarding bugs when appropriate).

Help a Debian developer

Paul Tagliamonte once blogged Hey, DDs, need help?. He offered his help to “overworked Debian developers”. His post was missing all the information required (cf motivations/skills/time) but the approach is a good one.

The best way to start contributing is to work with existing Debian developers. Even if you “just” want to be sponsored for your own pet package, you should consider that mentoring is a burden for many Debian developers and that you’re more likely to get a sponsor if you have an existing relationship with a Debian developer that you helped. Pick a developer that works in an area that is of interest, and offer him your help.

To simplify things even further, I have created a wiki page where you can find out how you can help me and thus build a relationship with me.

That’s it for now, I hope this article will help you to start contributing. Don’t forget to subscribe to my newsletter to not miss future articles for new contributors. Note that you can refer to this article with the following URL: https://raphaelhertzog.com/go/contributing/ (easier to type and remember).

PS: You might want to also check my Contributing to Debian page.

Deciphering one of dpkg’s weirdest errors: short read on buffer copy

June 27, 2011 by Raphaël Hertzog

As a Debian/Ubuntu user, you’re likely to be exposed at some point to an error reported by dpkg. In a series of articles, I’ll explain some of the errors that you might encounter.

Some error messages can be confusing at times. Most of the error strings do not appear very often and developers thus tend to use very terse description of the underlying problem. In other cases the architecture of the software makes it difficult to pin-point the real problem because the part that displays the error is several layers above the one that generated the initial error.

This is for example the case with this error of dpkg:

Unpacking replacement xulrunner-1.9.2 ...
dpkg-deb (subprocess): data: internal gzip read error: '<fd:0>: too many length or distance symbols'
dpkg-deb: error: subprocess <decompress> returned error exit status 2
dpkg: error processing /var/cache/apt/archives/xulrunner-1.9.2_1.9.2.17+build3+nobinonly-0ubuntu1_amd64.deb (--unpack):
 short read on buffer copy for backend dpkg-deb during `./usr/lib/xulrunner-1.9.2.17/components/libdbusservice.so'

First, the decompression layer discovers something unexpected in the data read in the .deb file and dpkg-deb outputs the error message coming from zlib (“too many length or distance symbols”). This causes the premature end of dpkg-deb --fsys-tarfile that dpkg had executed to extract the .data.tar archive from the deb file. In turn, dpkg informs us that dpkg-deb did not send all the data that were announced (and hence the “short read” in the error message) and that were meant to be part of the file ‘/usr/lib/xulrunner-1.9.2.17/components/libdbusservice.so’.

That’s all nice but it doesn’t help you much in general. What you must understand from the above is that the .deb file is corrupted (sometimes just truncated). In theory it should not happen since APT verifies the checksums of files when they are downloaded. But computers are not infallible and even if the downloaded data was good, it can have been corrupted when stored on disk (for example cheap SSD disks are known to not last very well).

Try removing the file (usually with apt-get clean since it’s stored in APT’s cache) and let APT download it again. Chances are that it will work on the second try. Otherwise consider doing a memory and HDD check as something is probably broken in your computer.

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apt-get, aptitude, … pick the right Debian package manager for you

June 20, 2011 by Raphaël Hertzog

This is a frequently asked question: “What package manager shall I use?”. And my answer is “the one that suits your needs”. In my case, I even use different package managers depending on what I’m trying to do.

APT vs dpkg, which one is the package manager?

In the Debian world, we’re usually thinking of APT-based software when we’re referring to a “package manager”. But in truth, the real package manager is dpkg. It’s the low-level tool that takes a .deb file and extracts its content on the disk, or that takes the name of a package to remove the associated files, etc.

APT is better known because it’s the part of the packaging infrastructure that matters to the user. APT makes collection of software available to the user and does the dirty work of downloading all the required packages and installing them by calling dpkg in the correct order to respect the dependencies.

But APT is not a simple program, it’s a library and several different APT frontends have been developed on top of that library. The most widely known is apt-get since it’s the oldest one, and it’s provided by APT itself.

Graphical APT front-ends

update-manager is a simple frontend useful to install security updates and other trivial daily upgrades (if you’re using testing or sid). It’s the one that you get when you click in the desktop notification that tells you that updates are available. In cases, where the upgrade is too complicated for update-manager, it will suggest to run synaptic which is full featured package manager. You can browse the list on installed/available packages in numerous ways, you can mark packages for installation/upgrade/removal/purge and then run in one go all the recorded actions.

software-center aims to be an easy to use application installer, it will hide most of the packaging details and will only present installed/available applications (as defined by a .desktop file). It’s very user friendly and has been developed by Ubuntu.

Of the graphical front-ends, I use mainly synaptic and only when I’m reviewing what I have installed to trim the system down.

Console-based GUI APT front-ends

In this category, I’ll cite only aptitude. Run without parameter, it will start a powerful console-based GUI. Much like synaptic, you can have multiple views of the installed/available packages and mark packages for installation/upgrade/removal/purge before executing everything at once.

Command-line based package managers and APT front-ends

This is where the well known apt-get fits, but there are several other alternatives: aptitude, cupt, wajig. Wajig and cupt are special cases as they don’t use libapt: the former wraps several tools including apt-get, and the latter is a (partial) APT reimplementation (versions 1.x were in Perl, 2.x are now is C++).

You’re welcome to try them out and find out which one you prefer, but I have never felt the need to use something else than apt-get and aptitude.

apt-get or aptitude?

First I want to make it clear that you can use both and mix them without problems. It used to be annoying when apt-get did not track which packages were automatically installed while aptitude did, but now that both packages share this list, there’s no reason to avoid switching back and forth.

I would recommend apt-get for the big upgrades (i.e. dist-upgrade from one stable to the next) because it will always find quickly a relatively good solution while aptitude can find several convoluted solutions (or none) and it’s difficult to decide which one should be used.

On the opposite for regular upgrades in unstable (or testing), I would recommend “aptitude safe-upgrade“. It does a better job than apt-get at keeping on hold packages which are temporarily broken due to some not yet finished changes while still installing new packages when required. With aptitude it’s also possible to tweak dynamically the suggested operations while apt-get doesn’t allow this. And aptitude’s command line is probably more consistent: with apt-get you have to switch between apt-get and apt-cache depending on the operation that you want to do, aptitude on the other hand does everything by itself.

Take some time to read their respective documentation and to try them.

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Why you should always have a network connection when installing Debian

June 13, 2011 by Raphaël Hertzog

This is a simple tip but an important one: when you’re installing Debian, take the time required to ensure the machine is connected to the Internet with a wired connection. If you have DHCP available, the debian-installer will use it to configure the network.

Why not use the wireless connection?

Because debian-installer in Squeeze doesn’t support WPA encryption, but only WEP. So if you’re using WPA, picking the wireless connection will lead to no working network during the installation and this is to be avoided.

If you’re still using WEP, you can go ahead of course.

If you only have a wireless connection with WPA, your might want to help the debian-installer team and add the required support. Matthew Palmer did some work on it a few months ago (see this mail and his branch in the netcfg git repository) but he resigned from the d-i team in the mean time. So WPA support is still not available in the wheezy debian-installer.

Why is the network so important?

The “tasks” that you select during the installation process might suggest installation of supplementary packages that are not available on your installation disc. If you install without network, the resulting system might differ from the expected one since it will be missing some packages that are available in the Debian repositories but not on your installation disc.
Your installation media might be old and there are security updates that have been published. If you do your initial installation with network, the security updates will be installed before the reboot and thus before the services are exposed over the network.
If you’re not installing a desktop with network-manager (Debian’s default GNOME Desktop provides it), the initial network configuration is important since this configuration is kept for the future. And you surely want network connectivity on your machine, don’t you?
Without network, APT’s sources.list will not be properly configured to include an HTTP mirror of your country. And really, I prefer when apt-get install can work without the initial installation disc.

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