README.md

   1 APT
   2 ===
   3
   4 apt is the main commandline package manager for Debian and its derivatives.
   5 It provides commandline tools for searching and managing as well as querying
   6 information about packages as well as low-level access to all features
   7 provided by the libapt-pkg and libapt-inst libraries which higher-level
   8 package managers can depend upon.
   9
  10 Included tools are:
  11
  12 * apt-get for retrieval of packages and information about them
  13   from authenticated sources and for installation, upgrade and
  14   removal of packages together with their dependencies
  15 * apt-cache for querying available information about installed
  16   as well as installable packages
  17 * apt-cdrom to use removable media as a source for packages
  18 * apt-config as an interface to the configuration settings
  19 * apt-key as an interface to manage authentication keys
  20 * apt-extracttemplates to be used by debconf to prompt for configuration
  21   questions before installation.
  22 * apt-ftparchive creates Packages and other index files
  23   needed to publish an archive of debian packages
  24 * apt-sortpkgs is a Packages/Sources file normalizer.
  25
  26 The libraries libapt-pkg and libapt-inst are also maintained as part of this project,
  27 alongside various additional binaries like the acquire-methods used by them.
  28 Bindings for Python ([python-apt](https://tracker.debian.org/pkg/python-apt)) and
  29 Perl ([libapt-pkg-perl](https://tracker.debian.org/pkg/libapt-pkg-perl)) are available as separated projects.
  30
  31 Discussion happens mostly on [the mailinglist](mailto:deity@lists.debian.org) ([archive](https://lists.debian.org/deity/)) and on [IRC](irc://irc.oftc.net/debian-apt).
  32 Our bugtracker as well as a general overview can be found at the [Debian Tracker page](https://tracker.debian.org/pkg/apt).
  33
  34
  35 Contributing
  36 ------------
  37 APT is maintained in git, the official repository being located at
  38 `git://anonscm.debian.org/apt/apt.git` ([webgit](http://anonscm.debian.org/gitweb/?p=apt/apt.git)),
  39 but also available at other locations like [GitHub](https://github.com/Debian/apt).
  40
  41 The default branch is `master`, other branches targeted at different
  42 derivatives and releases being used as needed. Various topic branches in
  43 different stages of completion might be branched of from those, which you
  44 are encouraged to do as well.
  45
  46 ### Coding
  47
  48 APT uses its own autoconf based build system, see [README.make](http://anonscm.debian.org/gitweb/?p=apt/apt.git;a=blob;f=README.make)
  49 for the glory details, but to get started, just run:
  50
  51         $ make
  52
  53 from a fresh git checkout.
  54
  55 The source code uses in most parts a relatively uncommon indent convention,
  56 namely 3 spaces with 8 space tab (see [doc/style.txt](http://anonscm.debian.org/gitweb/?p=apt/apt.git;a=blob;f=doc/style.txt) for more on this).
  57 Adhering to it avoids unnecessary code-churn destroying history (aka: `git blame`)
  58 and you are therefore encouraged to write patches in this style.
  59 Your editor can surely help you with this, for vim the settings would be
  60 `setlocal shiftwidth=3 noexpandtab tabstop=8`
  61 (the later two are the default configuration and could therefore be omitted).
  62
  63 ### Translations
  64
  65 While we welcome contributions here, we highly encourage you to contact the [Debian Internationalization (i18n) team](https://wiki.debian.org/Teams/I18n).
  66 Various language teams have formed which can help you creating, maintaining
  67 and improving a translation, while we could only do a basic syntax check of the
  68 file format…
  69
  70 Further more, Translating APT is split into two independent parts:
  71 The program translation, meaning the messages printed by the tools,
  72 as well as the manpages and other documentation shipped with APT.
  73
  74 ### Bug triage
  75
  76 Software tools like APT which are used by thousands of users every
  77 day have a steady flow of incoming bugreports. Not all of them are really
  78 bugs in APT: It can be packaging bugs like failing maintainer scripts a
  79 user reports against apt, because apt was the command he executed leading
  80 to this failure or various wishlist items for new features. Given enough time
  81 also the occasional duplicate enters the system.
  82 Our bugtracker is therefore full with open bugreports which are waiting for you! ;)
  83
  84 Testing
  85 -------
  86
  87 ### Manual execution
  88
  89 When you make changes and want to run them manually, make sure your
  90 `$LD_LIBRARY_PATH` points to the libraries you have built, e.g. via:
  91
  92         $ export LD_LIBRARY_PATH=$(pwd)/build/bin
  93         $ ./build/bin/apt-get moo
  94
  95
  96 ### Integration tests
  97
  98 There is a extensive integration testsuite available which can be run via:
  99
 100         $ ./test/integration/run-tests
 101
 102 While these tests are not executed at package build-time as they require additional
 103 dependencies, the repository contains the configuration needed to run them on [Travis CI](https://travis-ci.org/)
 104 as well as via autopkgtests e.g. on [Debian Continuous Integration](http://ci.debian.net/?q=apt#package/apt).
 105
 106 A testcase here is a shellscript embedded in a framework creating an environment in which
 107 apt tools can be used naturally without root-rights to test every aspect of its behavior
 108 itself as well as in conjunction with dpkg and other tools while working with packages.
 109
 110
 111 ### Unit tests
 112
 113 These tests are gtest-dev based, reside in `./test/libapt` and can be run with `make test`.
 114 They are executed at package build-time, but not by `make`.
 115
 116 Debugging
 117 ---------
 118
 119 APT does many things, so there is no central debug mode which could be
 120 activated. It uses instead various config-options to activate debug output
 121 in certain areas. The following describes some common scenarios and generally
 122 useful options, but is in no way exhaustive.
 123
 124 Note that you should *NEVER* use these settings as root to avoid accidents.
 125 Similation mode (`-s`) is usually sufficient to help you run apt as a non-root user.
 126
 127 ### Using different state files
 128
 129 If a dependency solver bug is reported, but can't be reproduced by the
 130 triager easily, it is beneficial to ask the reporter for the
 131 `/var/lib/dpkg/status` file, which includes the packages installed on the
 132 system and in which version. Such a file can then be used via the option
 133 `dir::state::status`. Beware of different architecture settings!
 134 Bugreports usually include this information in the template. Assuming you
 135 already have the `Packages` files for the architecture (see `sources.list`
 136 manpage for the `arch=` option) you can change to a different architecture
 137 with a config file like:
 138
 139         APT::Architecture "arch1";
 140         #clear APT::Architectures;
 141         APT:: Architectures { "arch1"; "arch2"; }
 142
 143 If a certain mirror state is needed, see if you can reproduce it with [snapshot.debian.org](http://snapshot.debian.org/).
 144 Your sources.list file (`dir::etc::sourcelist`) has to be correctly mention the repository,
 145 but if it does, you can use different downloaded archive state files via `dir::state::lists`.
 146
 147 In case manually vs. automatically installed matters, you can ask the reporter for
 148 the `/var/lib/apt/extended_states` file and use it with `dir::state::extended_states`.
 149
 150 ### Dependency resolution
 151
 152 APT works in its internal resolver in two stages: First all packages are visited
 153 and marked for installation, keep back or removal. Option `Debug::pkgDepCache::Marker`
 154 shows this. This also decides which packages are to be installed to satisfy dependencies,
 155 which can be seen by `Debug::pkgDepCache::AutoInstall`. After this is done, we might
 156 be in a situation in which two packages want to be installed, but only on of them can be.
 157 It is the job of the pkgProblemResolver to decide which of two packages 'wins' and can
 158 therefore decide what has to happen. You can see the contenders as well as their fight and
 159 the resulting resolution with `Debug::pkgProblemResolver`.
 160
 161 ### Downloading files
 162
 163 Various binaries (called 'methods') are tasked with downloading files. The Acquire system
 164 talks to them via simple text protocol. Depending on which side you want to see, either
 165 `Debug::pkgAcquire::Worker` or `Debug::Acquire::http` (or similar) will show the messages.
 166
 167 The integration tests use a simple self-built webserver which also logs. If you find that
 168 the http(s) methods do not behave like they should be try to implement this behavior in the
 169 webserver for simpler and more controlled testing.
 170
 171 ### Installation order
 172
 173 Dependencies are solved, packages downloaded: Everything read for the installation!
 174 The last step in the chain is often forgotten, but still very important:
 175 Packages have to be installed in a particular order so that their dependencies are
 176 satisfied, but at the same time you don't want to install very important and optional
 177 packages at the same time if possible, so that a broken optional package does not
 178 block the correct installation of very important packages. Which option to use depends on
 179 if you are interested in the topology sorting (`Debug::pkgOrderList`), the dependency-aware
 180 cycle and unconfigured prevention (`Debug::pkgPackageManager`) or the actual calls
 181 to dpkg (`Debug::pkgDpkgPm`).