The Mancoosi Team has recently published the details of a study we conducted analyzing different packages managers available in debian. The goal of this study was to compare MPM (the mancoosi package manager) to other legacy solvers and try to get a big picture regarding of the state of the art. A similar study was conduct during EDOS and the results are still available here.

As I wrote few months ago, MPM is a proof of concept that we wrote to test the behavior of a number of solvers that have been developed for the MISC competition in a real world scenario.

These results do not show anything new w.r.t. the experience of a lot of poeple dueling daily with their machines in order to install a new piece of software. In a nutshell, we have shown that apt-get, aptitude, smart and cupt perform pretty well when used only with one baseline (for example a stable release) : this conforms with the experience of the majority of users of debian based systems. However problems start to arise when a user start mixing more then one baseline putting a lot of stress on the solver in order to find a satisfying solution. This solution of course exists, but it is cleverly hidden in the dependency structure of more then 40K packages…

MPM is not as fast as other package solvers (say 10 seconds for mpm, while apt-get is able to find a solution in 3 second), but is remarkably stable. It is always able to find a satisfying solution, even in the harder cases where all the other failed. In these experiments MPM uses the postdam solver aspcud. This solver uses only GPL components and it would be a good candidate for inclusion in debian (there are actually a couple of ITP already filled for clasp and gringo).

The results (with a lot of details) are published on the mancoosi website (a more detailed report is in the works). Enjoy !

During fosdem the Mancoosi team that authored this work (Roberto, Ralf, Zack and Me) will be around, so, please stop us for a chat ! And don’t miss Ralf’s talk !!

In december we published the results of the third run of the misc live competition on the mancoosi website. I left this post in my draft folder for a quite a while now. I’ll publish for posterity…

The main difference from the last misc competition is the introduction of a new track, the user track, where we we want to answer the user request, and look for an optimal solution according to an optimization criterion provided by the user.

The initial assessment of the results are quite positive. We received 6 submissions for the trendy and paranoid track and 4 for the user track. These are very interesting results. We don’t have a clear winner on all tracks as in the misc 2010 competition. The cudf2msu4trendy-1.0 from INESC wins the trandy and user1 track. The aspcud-paranoid-1.3 from the university of posdam is the best on the paranoid track, while cudf2pbo4user-1.0 is the winner of the track user2 and user2.

The track paranoid and trendy are the same as in misc 2010. We actually used the same problems as in misc2010 plus 4 new categories (sarge…sid) that are a collection of problems featuring the same installation request but with increasingly large number of packages and versions per packages.

A few words on the new user track. Since in this track the optimization function was given to the solver as an additional input, we decided to try out different criteria. The first one, in user1 is what I called the “Paranoid upgrade” criteria and all problems used in this track are (real) upgrade problems. In cudf the upgrade semantic allow to effectively not upgrade at all a package (since in the solution its version must be greater or equal or the version currently installed). This definition does not goes very well together with the paranoid criteria as the best solution for an upgrade would always be a solution that do not change anything. For this reason the we defined the new criteria as ‘-notuptodate,-removed,-changed’ where solutions that privilege new (upgraded) packages are preferred to solution that do not change anything at all.

This is the second post about distcheck. I want to give a quick overview of the differences between edos-distcheck and the new version. First despite using the same sat solver and encoding of the problem, Distcheck has been re-written from scratch. Dose2 has several architectural problems and not very well documented. Adding new features had become too difficult and error-prone, so this was a natural choice (at least for me). Hopefully Dose3 will survive the Mancoosi project and provide a base for dependency reasoning. The framework is well documented and the architecture pretty modular. It’s is written in ocaml, so sadly, I don’t expect many people to join the development team, but we’ll be very open to it.

These are the main differences with edos-debcheck .

Performances

distcheck is about two times faster than edos-debcheck (from dose2), but it is a “bit” slower then debcheck (say the original debcheck), that is the tool wrote by Jerome Vouillon and that was then superseded in debian by edos-debcheck. The original debcheck was a all-in-one tool that did the parsing, encoding and solving without converting the problem to any intermediate format. distcheck trades a bit of speed for generality. Since it is based on Cudf, it can handle different formats and can be easily adapted in a range of situation just by changing the encoding of the original problem to cudf.

Below there are a couple of test I’ve performed on my machine (debian unstable). The numbers speak alone.

$time cat tmp/squeeze.packages | edos-debcheck -failures > /dev/null
Completing conflicts...                                            * 100.0%
Conflicts and dependencies...                                      * 100.0%
Solving                                                            * 100.0%

real    0m19.515s
user    0m19.193s
sys 0m0.276s

$time ./distcheck.native -f deb://tmp/squeeze.packages > /dev/null

real    0m10.859s
user    0m10.669s
sys 0m0.172s

Input

The second big difference is about different input format. In fact, at the moment, we have two different tools in debian, one edos-debcheck and the other edos-rpmcheck. Despite using the same underlying library these two tools have different code bases. distcheck basically is a multiplexer that convert different inputs to a common format and then uses it (agnostically) to solve the installation problem. It can be called in different ways (via symlinks) to behave similarly to its predecessors.

At the moment we are able to handle 5 different formats

deb:// Packages 822 format for debian based distributions

hdlist:// a binary format used by rpm based distribution

synth:// a simplified format to describe rpm based package

repositories

eclipse:// a 822 based format that encoded OSGi plugings metadata

cudf:// the native cudf format

distcheck handles gz and bz2 compressed file transparently . However if you care about performances, you should decompress your input file first and the parse it with distcheck and it often takes more time to decompress the file on the fly that run the installability test itself. There is also an experimental database backend that is not compiled by default at them moment.

Output

Regarding the output, I’ve already explained the main differences in an old post. As a quick reminder, the old edos-debcheck had two output options. The first is a human readable - unstructured output - that was a handy source of information when running the tool interactively. The second was a xml based format (without a dtd or a schema, I believe) that was used for batch processing.

distcheck has only one output type in the YAML format that aims to be human and machine readable. Hopefully this will cater for both needs. Moreover, just recently I’ve added the output of distcheck a summary of who is breaking what. The output of edos-debcheck was basically a map of packages to the reasons of the breakage. In addition to this information distcheck gives also a maps between reason (a missing dependency or a conflict) to the list of packages that are broken by this problem.This additional info is off by default, but I think it can be nice to know what is the missing dependency that is responsible for the majority of problems in a distribution…

For example, calling distcheck with —summary :

$./distcheck.native --summary deb://tests/sid.packages 
backgroud-packages: 29589
foreground-packages: 29589
broken-packages: 143
missing-packages: 138
conflict-packages: 5
unique-missing-packages: 52
unique-conflict-packages: 5
summary:
 -
  missing:
   missingdep: libevas-svn-05-engines-x (>= 0.9.9.063)
   packages:
    -
     package: enna-dbg
     version: 0.4.0-4
     architecture: amd64
     source: enna (= 0.4.0-4)
    -
     package: enna
     version: 0.4.0-4
     architecture: amd64
     source: enna (= 0.4.0-4)
 -
  missing:
   missingdep: libopenscenegraph56 (>= 2.8.1)
   packages:
    -
     package: libosgal1
     version: 0.6.1-2+b3
     architecture: amd64
     source: osgal (= 0.6.1-2)
    -
     package: libosgal-dev
     version: 0.6.1-2+b3
     architecture: amd64
     source: osgal (= 0.6.1-2)

Below I give a small example of the edos-debcheck output compared to the new yaml based output.

$cat tests/sid.packages | edos-debcheck -failures -explain
Completing conflicts...                                            * 100.0%
Conflicts and dependencies...                                      * 100.0%
Solving                                                            * 100.0%
zope-zms (= 1:2.11.1-03-1): FAILED
  zope-zms (= 1:2.11.1-03-1) depends on missing:
  - zope2.10
  - zope2.9
zope-tinytableplus (= 0.9-19): FAILED
  zope-tinytableplus (= 0.9-19) depends on missing:
  - zope2.11
  - zope2.10
  - zope2.9
...

And an extract from the distcheck output (the order is different. I cut and pasted parts of the output here…)

$./distcheck.native -f -e deb://tests/sid.packages
report:
 -
  package: zope-zms
  version: 1:2.11.1-03-1
  architecture: all
  source: zope-zms (= 1:2.11.1-03-1)
  status: broken
  reasons:
   -
    missing:
     pkg:
      package: zope-zms
      version: 1:2.11.1-03-1
      architecture: all
      missingdep: zope2.9 | zope2.10
 -
  package: zope-tinytableplus
  version: 0.9-19
  architecture: all
  source: zope-tinytableplus (= 0.9-19)
  status: broken
  reasons:
   -
    missing:
     pkg:
      package: zope-tinytableplus
      version: 0.9-19
      architecture: all
      missingdep: zope2.9 | zope2.10 | zope2.11
...

Future

The roadmap to release version 1.0 of distcheck is as follows:

add background and foreground package selection. This feature will

allow the use to specify a larger universe (background packages), but check only a subset of this universe (foreground packages). This should allow users to select packages using grep-dctrl and then pipe them to discheck . At the moment we can select individual packages on the command line or we can use expression like bash (<= 2.7) to check all version of bash in the universe with version greater than 2.7.

code cleanup and a bit of refactoring between distcheck and

buildcheck (that is a frontend for distcheck that allow us to report broken build dependencies)

consider essential packages while performing the installation test.

Here there are few things we have to understand, but the idea would be to detect possible problems related the implicit presence of essential packages in the distribution. At the moment, distcheck performs the installation test in the empty universe, while ideally, the universe should contain all essential packages.

finish the documentation. The effort in underway and we hope to

finalize shortly to release the debian package in experimental.

Here at mancoosi we have been working for quite a while to promote and advance solver technology for FOSS distributions. We are almost at the end of the project and it is important to make the mancoosi technology relevant for the community. On goal of the project is to provide a prototype that uses part of the results of mancoosi that can based to install/remove/upgrade packages on a user machine. We certainly don’t want to create yet another meta installer. This would be very time consuming and certainly going beyond the scope of the project. The idea is to create a prototype, that can work as an apt-get drop in replacement that will allow everybody to play with different solvers and installation criteria.

A very first integration step is a small shell script apt-mancoosi that tries to put together different tools that we have implemented during the project. Roberto wrote extensively about his experience with apt-mancoosi a while ago showing that somehow the mancoosi tools are already usable, as proof of concept, to experiment with all solvers participating to the Misc competition.

On notable obstacle we encountered with apt-mancoosi is how to pipe the result of an external solver to apt-get to effectively install the packages proposed as solution. Apt-mancoosi fails to be a drop-in replacement for apt-get exactly for this reason.

The “problem” is quite simple : The idea at the beginning was to pass to apt-get, on the command line, a request that effectively represents a complete solution. We expected that, since this was already a locked-down solution, apt-get would have just installed all packages without any further modification to the proposed installation set. Of course, since apt-get is designed to satisfy a user request, and not just to install packages, we quickly realized that our evil plan was doomed to failure.

The only option left, was to use libapt directly, but the idea of programming in c++ quickly made me to desist. After a bit of research (not that much after all), I finally found a viable solution to our problems in python-apt that is a low level and wrapper around libapt. This definitely made my day.

Now the juicy details. the problem was to convince apt to completely bypass the solver part and just call the installer. First a small intro. python-apt has an extensive documentation with a couple of tutorials. Using python-apt is actually pretty easy (some snippet from the python-apt doco) :

import apt

# First of all, open the cache
cache = apt.Cache()
# Now, lets update the package list
cache.update()

here we open the cache (apt.Cache is a wrapper around the low level binding in the apt_pkg module), then we update the package list. This is equivalent to apt-get update . Installing a package is equally easy :

import apt
cache = apt.Cache()
pkg = cache['python-apt']

# Mark python-apt for install
pkg.mark_install()

# Now, really install it
cache.commit()

Now, the method mark_install of the module package will effectively run the solver to resolve and mark all the dependencies of the package python-apt. This is the default behavior when apt-get is used on the command line. This method has however three optional arguments that are just what I was looking for, that is autoFix, autoInst and fromUser . The explanation from the python-apt doco is quite clear.

mark_install(*args, **kwds)
    Mark a package for install.
    If autoFix is True, the resolver will be run, trying to fix broken packages. This is the default.
    If autoInst is True, the dependencies of the packages will be installed automatically. This is the default.
    If fromUser is True, this package will not be marked as automatically installed. This is the default. Set it to False if you want to be able to automatically remove the package at a later stage when no other package depends on it.

What we want is to set autoFix and autoInst to false to completely bypass the solver. So imagine that an external solver can give use a string of the form : bash+ dash=1.4 baobab- that basically asks to install bash to the newest version, dash at version 1.4 and remove baobab. Suppose also that this is a complete solution, that is, all dependencies are satisfied and there are no conflicts.

The work flow of mpm (mancoosi package manager) is as follows : init apt-get, convert all packages lists + status in a cudf description, pass this cudf to an external solver, get the result and set all packages to add/remove in the apt.cache of python-apt download the packages commit the changes (effectively, run dpkg)

We already have a first prototype on the mancoosi svn. It’s not released yet as we are waiting to do more testing, add more options and make it stable enough for testing. Maybe one day, this will be uploaded to debian.

This is the trace of a successful installation of a package in a lenny chroot. The solver used here is the p2 solver

dev:~/mpm# ./mpm.py -c apt.conf install baobab
Running p2cudf-paranoid-1.6 solver ...
Validate solution ...
loading CUDF ...
loading solution ...
Summary of proposed changes:
 new: 30
 removed: 0
 replaced: 0
 upgraded: 0
 downgraded: 0
 unsatisfied recommends:: 8
 changed: 30
 uptodate: 322
 notuptodate: 116

New packages: baobab (2.30.0-2) dbus-x11 (1.2.24-3) gconf2 (2.28.1-5)
 gconf2-common (2.28.1-5) gnome-utils-common (2.30.0-2)
 libatk1.0-0 (1.30.0-1) libcairo2 (1.8.10-6) libdatrie1 (0.2.4-1)
 libdbus-glib-1-2 (0.88-2) libgconf2-4 (2.28.1-5) libgtk2.0-0 (2.20.1-2)
 libgtk2.0-common (2.20.1-2) libgtop2-7 (2.28.1-1) libgtop2-common (2.28.1-1)
 libidl0 (0.8.14-0.1) libjasper1 (1.900.1-7+b1) liborbit2 (1:2.14.18-0.1)
 libpango1.0-0 (1.28.3-1) libpango1.0-common (1.28.3-1)
 libpixman-1-0 (0.16.4-1) libthai-data (0.1.14-2) libthai0 (0.1.14-2)
 libtiff4 (3.9.4-5) libxcb-render-util0 (0.3.6-1) libxcb-render0 (1.6-1)
 libxcomposite1 (1:0.4.2-1) libxcursor1 (1:1.1.10-2) libxrandr2 (2:1.3.0-3)
 psmisc (22.11-1) shared-mime-info (0.71-3) 
Removed packages: 
Replaced packages: 
Upgraded packages: 

Selecting previously deselected package libatk1.0-0.
(Reading database ... 28065 files and directories currently installed.)
Unpacking libatk1.0-0 (from .../libatk1.0-0_1.30.0-1_i386.deb) ...
Selecting previously deselected package libpixman-1-0.
Unpacking libpixman-1-0 (from .../libpixman-1-0_0.16.4-1_i386.deb) ...
Selecting previously deselected package libxcb-render0.
Unpacking libxcb-render0 (from .../libxcb-render0_1.6-1_i386.deb) ...
Selecting previously deselected package libxcb-render-util0.
Unpacking libxcb-render-util0 (from .../libxcb-render-util0_0.3.6-1_i386.deb) ...
Selecting previously deselected package libcairo2.
Unpacking libcairo2 (from .../libcairo2_1.8.10-6_i386.deb) ...
Selecting previously deselected package libdbus-glib-1-2.
Unpacking libdbus-glib-1-2 (from .../libdbus-glib-1-2_0.88-2_i386.deb) ...
Selecting previously deselected package libidl0.
Unpacking libidl0 (from .../libidl0_0.8.14-0.1_i386.deb) ...
Selecting previously deselected package liborbit2.
Unpacking liborbit2 (from .../liborbit2_1%3a2.14.18-0.1_i386.deb) ...
Selecting previously deselected package gconf2-common.
Unpacking gconf2-common (from .../gconf2-common_2.28.1-5_all.deb) ...
Selecting previously deselected package libgconf2-4.
Unpacking libgconf2-4 (from .../libgconf2-4_2.28.1-5_i386.deb) ...
Selecting previously deselected package libgtk2.0-common.
Unpacking libgtk2.0-common (from .../libgtk2.0-common_2.20.1-2_all.deb) ...
Selecting previously deselected package libjasper1.
Unpacking libjasper1 (from .../libjasper1_1.900.1-7+b1_i386.deb) ...
Selecting previously deselected package libpango1.0-common.
Unpacking libpango1.0-common (from .../libpango1.0-common_1.28.3-1_all.deb) ...
Selecting previously deselected package libdatrie1.
Unpacking libdatrie1 (from .../libdatrie1_0.2.4-1_i386.deb) ...
Selecting previously deselected package libthai-data.
Unpacking libthai-data (from .../libthai-data_0.1.14-2_all.deb) ...
Selecting previously deselected package libthai0.
Unpacking libthai0 (from .../libthai0_0.1.14-2_i386.deb) ...
Selecting previously deselected package libpango1.0-0.
Unpacking libpango1.0-0 (from .../libpango1.0-0_1.28.3-1_i386.deb) ...
Selecting previously deselected package libtiff4.
Unpacking libtiff4 (from .../libtiff4_3.9.4-5_i386.deb) ...
Selecting previously deselected package libxcomposite1.
Unpacking libxcomposite1 (from .../libxcomposite1_1%3a0.4.2-1_i386.deb) ...
Selecting previously deselected package libxcursor1.
Selecting previously deselected package libxrandr2.
Unpacking libxrandr2 (from .../libxrandr2_2%3a1.3.0-3_i386.deb) ...
Selecting previously deselected package shared-mime-info.
Unpacking shared-mime-info (from .../shared-mime-info_0.71-3_i386.deb) ...
Selecting previously deselected package libgtk2.0-0.
Unpacking libgtk2.0-0 (from .../libgtk2.0-0_2.20.1-2_i386.deb) ...
Selecting previously deselected package libgtop2-common.
Unpacking libgtop2-common (from .../libgtop2-common_2.28.1-1_all.deb) ...
Selecting previously deselected package libgtop2-7.
Unpacking libgtop2-7 (from .../libgtop2-7_2.28.1-1_i386.deb) ...
Selecting previously deselected package psmisc.
Unpacking psmisc (from .../psmisc_22.11-1_i386.deb) ...
Selecting previously deselected package dbus-x11.
Unpacking dbus-x11 (from .../dbus-x11_1.2.24-3_i386.deb) ...
Selecting previously deselected package gconf2.
Unpacking gconf2 (from .../gconf2_2.28.1-5_i386.deb) ...
Selecting previously deselected package gnome-utils-common.
Unpacking gnome-utils-common (from .../gnome-utils-common_2.30.0-2_all.deb) ...
Selecting previously deselected package baobab.
Unpacking baobab (from .../baobab_2.30.0-2_i386.deb) ...
Processing triggers for man-db ...
Setting up libatk1.0-0 (1.30.0-1) ...
Setting up libpixman-1-0 (0.16.4-1) ...
Setting up libxcb-render0 (1.6-1) ...
Setting up libxcb-render-util0 (0.3.6-1) ...
Setting up libcairo2 (1.8.10-6) ...
Setting up libdbus-glib-1-2 (0.88-2) ...
Setting up libidl0 (0.8.14-0.1) ...
Setting up liborbit2 (1:2.14.18-0.1) ...
Setting up gconf2-common (2.28.1-5) ...

Creating config file /etc/gconf/2/path with new version
Setting up libgconf2-4 (2.28.1-5) ...
Setting up libgtk2.0-common (2.20.1-2) ...
Setting up libjasper1 (1.900.1-7+b1) ...
Setting up libpango1.0-common (1.28.3-1) ...
Cleaning up font configuration of pango...
Updating font configuration of pango...
Cleaning up category xfont..
Updating category xfont..
Setting up libdatrie1 (0.2.4-1) ...
Setting up libthai-data (0.1.14-2) ...
Setting up libthai0 (0.1.14-2) ...
Setting up libpango1.0-0 (1.28.3-1) ...
Setting up libtiff4 (3.9.4-5) ...
Setting up libxcomposite1 (1:0.4.2-1) ...
Setting up libxcursor1 (1:1.1.10-2) ...
Setting up libxrandr2 (2:1.3.0-3) ...
Setting up shared-mime-info (0.71-3) ...
Setting up libgtk2.0-0 (2.20.1-2) ...
Setting up libgtop2-common (2.28.1-1) ...
Setting up libgtop2-7 (2.28.1-1) ...
Setting up psmisc (22.11-1) ...
Setting up dbus-x11 (1.2.24-3) ...
Setting up gconf2 (2.28.1-5) ...
update-alternatives: using /usr/bin/gconftool-2 to provide /usr/bin/gconftool (gconftool) in auto mode.
Setting up gnome-utils-common (2.30.0-2) ...
Setting up baobab (2.30.0-2) ...
Broken: 0 
InstCount: 30 
DelCount: 0 
dev:~/mpm# 

I think we’ll keep working on this python prototype for a while, but this is not certainly what we want to propose to the community. The mancoosi package manager is probably going to be written in Ocaml and integrated with dose3 and libcudf. This will allow us to gain speed and have a solid language to develop with (nothing against python, but we don’t feel that a scripting language is suitable for an essential component as a package manager). Time will tell. For the moment this is just vapor-ware …

A while ago I wrote about the new distcheck tool upcoming in dose3. I’ve recently updated the proposal on the debian wiki to reflect recent changes in the yaml data structure. The idea was to remove redundant information, to make it easier to read and at the same time include enough details to make it easy to use from a script. I’ll write down a small example to explain the format. A package can be broken because of a missing package or because of a conflict. For a missing package we’ll have a stanza like this :

  package: libgnuradio-dev
  version: 3.2.2.dfsg-1
  architecture: all
  source: gnuradio (= 3.2.2.dfsg-1)
  status: broken
  reasons:
   -
    missing:
     pkg:
      package: libgruel0
      version: 3.2.2.dfsg-1+b1
      architecture: amd64
      missingdep: libboost-thread1.40.0 (>= 1.40.0-1)
     paths:
      -
       depchain:
        -
         package: libgnuradio-dev
         version: 3.2.2.dfsg-1
         architecture: all
         depends: libgnuradio (= 3.2.2.dfsg-1)
        -
         package: libgnuradio
         version: 3.2.2.dfsg-1
         architecture: all
         depends: libgnuradio-core0
        -
         package: libgnuradio-core0
         version: 3.2.2.dfsg-1+b1
         architecture: amd64
         depends: libgruel0 (= 3.2.2.dfsg-1+b1)

The first part gives details about the package libgnuradio-dev, specifying its status, source and architecture. The second part is the reason of the problem. In this case it is a missing package that is essential to install libgnuradio-dev. missindep is the dependency that cannot be satisfied is the package libgruel0 , in this case: libboost-thread1.40.0 (>= 1.40.0-1).

The paths component gives all possible depchains from the root package libgnuradio-dev to libgruel0 . Notice that we do not include the last node in the dependency chain to avoid a useless repetition. Of course there might be more then on path to reach libgruel0. Distcheck will unroll all of them. Because of the structure of debian dependencies usually there are not so many paths.

The other possible cause of a problem is a conflict. Consider the following :

  package: a
  version: 1
  status: broken
  reasons:
   -
    conflict:
     pkg1:
      package: e
      version: 1
     pkg2:
      package: f
      version: 1
     depchain1:
      -
       depchain:
        -
         package: a
         version: 1
         depends: b
        -
         package: b
         version: 1
         depends: e
     depchain2:
      -
       depchain:
        -
         package: a
         version: 1
         depends: d
        -
         package: d
         version: 1
         depends: f

This is the general case of a deep conflict. I use an artificial example here instead of a concrete one since this case is not very common and I was not able to find one. To put everything in context, this is the example I’ve used (it’s in cudf format, but I think you get the gist of it):

package: a
version: 1
depends: b, d

package: b
version: 1
depends: e

package: d
version: 1
depends: f

package: f
version: 1
conflicts: e

package: e
version: 1
conflicts: f

The first part of the distcheck report is as before with details about the broken package. Since this is a conflict, and all conflicts are binary, we give the two packages involved in the conflict first. Packages f and e are in conflict, but they are not direct dependency of package a . For this reason, we output the two paths that from a lead to f or e. All dependency chains for each conflict are together. Again, since there might be more than one way from a to reach the conflicting packages, we can have more then one depchain.

Another important upcoming change is distcheck (to be implemented soon) it the ability to check if a package is in conflict with an Essential package. In the past edos-debcheck always check the installability of a package in the empty universe. This assumption is actually not true for debian as all essential packages should always be installed. For this reason, now distcheck will check the installability problem not in an empty universe, but in a universe with all essential packages installed.

This check is not going to be fool proof though. Because of the semantic of essential packages, despite is not possible to remove a package toutcourt, an essential package can be replaced by a non essential package via the replace mechanism. For example, poking with this feature I noticed that the package upstart in sid replace sysinit and it is in conflict with it. This is perfectly fine as it gives a mechanism to upgrade and replace essential components of the system. At the same time this does not fit in the edos-debcheck philosophy of checking packages for installation problems in the empty universe (or in a universe with all essential packages installed). At the moment we are still thinking how to address this problem (the solution will be in the long term to add the replace semantic in distcheck), but for the moment we will just provide an option to check packages w.r.t essential packages conscious the this can lead to false positives.

This work is of course done in collaboration with the mancoosi team in paris.

Dose3 is still not ready for prime time. We are preparing debian packages and we plan to upload them in experimental in the near feature.