Debian – Page 60

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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Installing GNOME 3 on Debian 6.0 Squeeze? No, sorry

June 16, 2011 by Raphaël Hertzog

Ever since I blogged about the status of GNOME 3 in Debian experimental, my web logs show that many people are looking for ways to try out GNOME 3 with Debian Squeeze.

No GNOME 3 for Debian 6.0

Don’t hold your breath, it’s highly unlikely that anyone of the Debian GNOME team will prepare backports of GNOME 3 for Debian 6.0 Squeeze. It’s already difficult enough to do everything right in unstable with a solid upgrade path from the current versions in Squeeze…

But if you are brave enough to want to install GNOME 3 with Debian 6.0 on your machine then I would suggest that you’re the kind of person who should run Debian testing instead (or even Debian unstable, it’s not so horrible). That’s what most people who like to run recent versions of software do.

How to run Debian testing

You’re convinced and want to run Debian testing? It’s really easy, just edit your /etc/apt/sources.list and replace “stable” with “testing”. A complete file could look like this:

# Main repository
deb http://ftp.debian.org/debian testing main contrib non-free
deb-src http://ftp.debian.org/debian testing main contrib non-free
# Security updates
deb http://security.debian.org/debian-security testing main contrib non-free

Now you should be able to run apt-get dist-upgrade and end up with a testing system.

How to install GNOME 3 on Debian testing aka wheezy

If you want to try GNOME 3 before it has landed in testing, you’ll have to add unstable and experimental to your sources.list:

deb http://ftp.debian.org/debian unstable main contrib non-free
deb http://ftp.debian.org/debian experimental main contrib non-free

You should not install GNOME 3 from experimental if you’re not ready to deal with some problems and glitches. Beware: once you upgraded to GNOME 3 it will be next to impossible to go back to GNOME 2.32 (you can try it, but it’s not officially supported by Debian).

To avoid upgrading all your packages to unstable, you will tell APT to prefer testing with the APT::Default-Release directive:

# cat >/etc/apt/apt.conf.d/local <<END
APT::Default-Release "testing";
END

To allow APT to upgrade the GNOME packages to unstable/experimental, you will also install the following pinning file as /etc/apt/preferences.d/gnome:

Package: *gnome* libglib2.0* *vte* *pulse* *peas* libgtk* *gjs* *gconf* *gstreamer* alacarte *brasero* cheese ekiga empathy* gdm3 gcalctool baobab *gucharmap* gvfs* hamster-applet *nautilus* seahorse* sound-juicer *totem* remmina vino gksu xdg-user-dirs-gtk dmz-cursor-theme eog epiphany* evince* *evolution* file-roller gedit* metacity *mutter* yelp* rhythmbox* banshee* system-config-printer transmission-* tomboy network-manager* libnm-* update-notifier shotwell liferea *software-properties* libunique-3.0-0 libseed-gtk3-0 libnotify* libpanel-applet-4-0 libgdata11 libcamel* libcanberra* libchamplain* libebackend* libebook* libecal* libedata* libegroupwise* libevent* gir1.2-* libxklavier16 python-gmenu libgdict-1.0-6 libgdu-gtk0
Pin: release experimental
Pin-Priority: 990

Package: *gnome* libglib2.0* *vte* *pulse* *peas* libgtk* *gjs* *gconf* *gstreamer* alacarte *brasero* cheese ekiga empathy* gdm3 gcalctool baobab *gucharmap* gvfs* hamster-applet *nautilus* seahorse* sound-juicer *totem* remmina vino gksu xdg-user-dirs-gtk dmz-cursor-theme eog epiphany* evince* *evolution* file-roller gedit* metacity *mutter* yelp* rhythmbox* banshee* system-config-printer transmission-* tomboy network-manager* libnm-* update-notifier shotwell liferea *software-properties* libunique-3.0-0 libseed-gtk3-0 libnotify* libpanel-applet-4-0 libgdata11 libcamel* libcanberra* libchamplain* libebackend* libebook* libecal* libedata* libegroupwise* libevent* gir1.2-* libxklavier16 python-gmenu libgdict-1.0-6 libgdu-gtk0
Pin: release unstable
Pin-Priority: 990

Package: *
Pin: release experimental
Pin-Priority: 150

Note that I used “Pin-Priority: 990” this time (while I used 500 in the article explaining how to install GNOME 3 on top of unstable), that’s because you want these packages to have the same priority than those of testing, and they have a priority of 990 instead of 500 due to the APT::Default-Release setting.

You’re done, your next dist-upgrade should install GNOME 3. It will pull a bunch of packages from unstable too but that’s expected since the packages required by GNOME 3 are spread between unstable and experimental.

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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.