Version 3.1.3
Copyright © 1998 Jason Gunthorpe
Abstract
This document provides an overview of how to use the APT package manager.
Table of Contents
Table of Contents
The APT package currently contains two sections, the APT dselect method and the apt-get command line user interface. Both provide a way to install and remove packages as well as download new packages from the Internet. |
The Debian packaging system has a large amount of information associated with each package to help assure that it integrates cleanly and easily into the system. The most prominent of its features is the dependency system. |
The dependency system allows individual programs to make use of shared elements in the system such as libraries. It simplifies placing infrequently used portions of a program in separate packages to reduce the number of things the average user is required to install. Also, it allows for choices in mail transport agents, X servers and so on. |
The first step to understanding the dependency system is to grasp the concept of a simple dependency. The meaning of a simple dependency is that a package requires another package to be installed at the same time to work properly. |
For instance, mailcrypt is an emacs extension that aids in encrypting email with GPG. Without GPGP installed mailcrypt is useless, so mailcrypt has a simple dependency on GPG. Also, because it is an emacs extension it has a simple dependency on emacs, without emacs it is completely useless. |
The other important dependency to understand is a conflicting dependency. It means that a package, when installed with another package, will not work and may possibly be extremely harmful to the system. As an example consider a mail transport agent such as sendmail, exim or qmail. It is not possible to have two mail transport agents installed because both need to listen to the network to receive mail. Attempting to install two will seriously damage the system so all mail transport agents have a conflicting dependency with all other mail transport agents. |
As an added complication there is the possibility for a package to pretend to be another package. Consider that exim and sendmail for many intents are identical, they both deliver mail and understand a common interface. Hence, the package system has a way for them to declare that they are both mail-transport-agents. So, exim and sendmail both declare that they provide a mail-transport-agent and other packages that need a mail transport agent depend on mail-transport-agent. This can add a great deal of confusion when trying to manually fix packages. |
At any given time a single dependency may be met by packages that are already installed or it may not be. APT attempts to help resolve dependency issues by providing a number of automatic algorithms that help in selecting packages for installation. |
apt-get provides a simple way to install packages from the command line. Unlike dpkg, apt-get does not understand .deb files, it works with the package's proper name and can only install .deb archives from a Source. |
The first [1] thing that should be done before using apt-get
is to fetch the package lists from the Sources so that it
knows what packages are available. This is done with |
# apt-get update Get http://ftp.de.debian.org/debian/ stable/binary-i386/ Packages Get http://llug.sep.bnl.gov/debian/ testing/contrib Packages Reading Package Lists... Done Building Dependency Tree... Done |
Once updated there are several commands that can be used: |
|
apt-get has several command line options that are detailed
in its man page,
apt-get(8). The
most useful option is |
[1] If you are using an http proxy server you must set the http_proxy environment variable first, see sources.list(5) |
The APT dselect method provides the complete APT system with the dselect package selection GUI. dselect is used to select the packages to be installed or removed and APT actually installs them. |
To enable the APT method you need to select [A]ccess in dselect and then choose the APT method. You will be prompted for a set of Sources which are places to fetch archives from. These can be remote Internet sites, local Debian mirrors or CD-ROMs. Each source can provide a fragment of the total Debian archive, APT will automatically combine them to form a complete set of packages. If you have a CD-ROM then it is a good idea to specify it first and then specify a mirror so that you have access to the latest bug fixes. APT will automatically use packages on your CD-ROM before downloading from the Internet. |
Set up a list of distribution source locations
Please give the base URL of the debian distribution.
The access schemes I know about are: http file
For example:
file:/mnt/debian,
https://deb.debian.org/debian,
http://deb.debian.org/debian,
URL [http://llug.sep.bnl.gov/debian]:
|
The Sources setup starts by asking for the base of the Debian archive, defaulting to an HTTP mirror. Next it asks for the distribution to get. |
Please give the distribution tag to get or a path to the package file ending in a /. The distribution tags are typically something like: stable unstable testing Distribution [stable]: |
The distribution refers to the Debian version in the archive, stable refers to the latest released version and unstable refers to the developmental version. |
Please give the components to get The components are typically something like: main contrib non-free non-free-firmware Components [main contrib non-free non-free-firmware]: |
The components list refers to the list of sub distributions to fetch. The distribution is split up based on software licenses, main being DFSG free packages while contrib and non-free contain things that have various restrictions placed on their use and distribution. |
Any number of sources can be added, the setup script will continue to prompt until you have specified all that you want. |
Before starting to use dselect it is necessary to update
the available list by selecting [U]pdate from the menu. This is a superset of
|
You can then go on and make your selections using [S]elect and then perform the installation using [I]nstall. When using the APT method the [C]onfig and [R]emove commands have no meaning, the [I]nstall command performs both of them together. |
By default APT will automatically remove the package (.deb) files once they
have been successfully installed. To change this behavior place
|
Table of Contents
Both that APT dselect method and apt-get share the same interface. It is a simple system that generally tells you what it will do and then goes and does it. [2] After printing out a summary of what will happen APT then will print out some informative status messages so that you can estimate how far along it is and how much is left to do. |
Before all operations except update, APT performs a number of actions
to prepare its internal state. It also does some checks of the system's
state. At any time these operations can be performed by running
|
# apt-get check Reading Package Lists... Done Building Dependency Tree... Done |
The first thing it does is read all the package files into memory. APT uses a caching scheme so this operation will be faster the second time it is run. If some of the package files are not found then they will be ignored and a warning will be printed when apt-get exits. |
The final operation performs a detailed analysis of the system's dependencies. It checks every dependency of every installed or unpacked package and considers if it is OK. Should this find a problem then a report will be printed out and apt-get will refuse to run. |
# apt-get check
Reading Package Lists... Done
Building Dependency Tree... Done
You might want to run 'apt --fix-broken install' to correct these.
Sorry, but the following packages have unmet dependencies:
9fonts: Depends: xlib6g but it is not installed
uucp: Depends: mailx but it is not installed
blast: Depends: xlib6g (>= 3.3-5) but it is not installed
adduser: Depends: perl-base but it is not installed
aumix: Depends: libgpmg1 but it is not installed
debiandoc-sgml: Depends: sgml-base but it is not installed
bash-builtins: Depends: bash (>= 2.01) but 2.0-3 is installed
cthugha: Depends: svgalibg1 but it is not installed
Depends: xlib6g (>= 3.3-5) but it is not installed
libreadlineg2: Conflicts:libreadline2 (<< 2.1-2.1)
|
In this example the system has many problems, including a serious problem with libreadlineg2. For each package that has unmet dependencies a line is printed out indicating the package with the problem and the dependencies that are unmet. A short explanation of why the package has a dependency problem is also included. |
There are two ways a system can get into a broken state like this. The first is caused by dpkg missing some subtle relationships between packages when performing upgrades. [3]. The second is if a package installation fails during an operation. In this situation a package may have been unpacked without its dependents being installed. |
The second situation is much less serious than the first because APT places
certain constraints on the order that packages are installed. In both cases
supplying the |
However, if the |
Before proceeding apt-get will present a report on what will
happen. Generally the report reflects the type of operation being performed
but there are several common elements. In all cases the lists reflect the
final state of things, taking into account the |
The following extra packages will be installed: libdbd-mysql-perl xlib6 zlib1 xzx libreadline2 libdbd-msql-perl mailpgp xdpkg fileutils pinepgp zlib1g xlib6g perl-base bin86 libgdbm1 libgdbmg1 quake-lib gmp2 bcc xbuffy squake pgp-i python-base debmake ldso perl libreadlineg2 ssh |
The Extra Package list shows all of the packages that will be installed or
upgraded in excess of the ones mentioned on the command line. It is only
generated for an |
The following packages will be REMOVED: xlib6-dev xpat2 tk40-dev xkeycaps xbattle xonix xdaliclock tk40 tk41 xforms0.86 ghostview xloadimage xcolorsel xadmin xboard perl-debug tkined xtetris libreadline2-dev perl-suid nas xpilot xfig |
The Packages to Remove list shows all of the packages that will be removed
from the system. It can be shown for any of the operations and should be given
a careful inspection to ensure nothing important is to be taken off. The
|
The following NEW packages will installed: zlib1g xlib6g perl-base libgdbmg1 quake-lib gmp2 pgp-i python-base |
The New Packages list is simply a reminder of what will happen. The packages listed are not presently installed in the system but will be when APT is done. |
The following packages have been kept back compface man-db tetex-base msql libpaper svgalib1 gs snmp arena lynx xpat2 groff xscreensaver |
Whenever the whole system is being upgraded there is the possibility that new
versions of packages cannot be installed because they require new things or
conflict with already installed things. In this case the package will appear
in the Kept Back list. The best way to convince packages listed there to
install is with |
The following held packages will be changed: cvs |
Sometimes you can ask APT to install a package that is on hold, in such a case it prints out a warning that the held package is going to be changed. This should only happen during dist-upgrade or install. |
Finally, APT will print out a summary of all the changes that will occur. |
206 packages upgraded, 8 newly installed, 23 to remove and 51 not upgraded. 12 packages not fully installed or removed. Need to get 65.7M/66.7M of archives. After unpacking 26.5M will be used. |
The first line of the summary simply is a reduced version of all of the lists and includes the number of upgrades - that is packages already installed that have new versions available. The second line indicates the number of poorly configured packages, possibly the result of an aborted installation. The final line shows the space requirements that the installation needs. The first pair of numbers refer to the size of the archive files. The first number indicates the number of bytes that must be fetched from remote locations and the second indicates the total size of all the archives required. The next number indicates the size difference between the presently installed packages and the newly installed packages. It is roughly equivalent to the space required in /usr after everything is done. If a large number of packages are being removed then the value may indicate the amount of space that will be freed. |
Some other reports can be generated by using the -u option to show packages to upgrade, they are similar to the previous examples. |
During the download of archives and package files APT prints out a series of status messages. |
# apt-get update Get:1 http://ftp.de.debian.org/debian/ stable/main Packages Get:2 http://llug.sep.bnl.gov/debian/ testing/contrib Packages Hit http://llug.sep.bnl.gov/debian/ testing/main Packages Get:4 http://ftp.de.debian.org/debian/ unstable/binary-i386/ Packages Get:5 http://llug.sep.bnl.gov/debian/ testing/non-free Packages 11% [5 testing/non-free `Waiting for file' 0/32.1k 0%] 2203b/s 1m52s |
The lines starting with Get are printed out when APT
begins to fetch a file while the last line indicates the progress of the
download. The first percent value on the progress line indicates the total
percent done of all files. Unfortunately since the size of the Package files
is unknown |
The next section of the status line is repeated once for each download thread and indicates the operation being performed and some useful information about what is happening. Sometimes this section will simply read Forking which means the OS is loading the download module. The first word after the [ is the fetch number as shown on the history lines. The next word is the short form name of the object being downloaded. For archives it will contain the name of the package that is being fetched. |
Inside of the single quote is an informative string indicating the progress of
the negotiation phase of the download. Typically it progresses from
Connecting to Waiting for file to
Downloading or Resuming. The final
value is the number of bytes downloaded from the remote site. Once the
download begins this is represented as |
The status display updates every half second to provide a constant feedback on
the download progress while the Get lines scroll back whenever a new file is
started. Since the status display is constantly updated it is unsuitable for
logging to a file, use the |
APT uses dpkg for installing the archives and will switch over to the dpkg interface once downloading is completed. dpkg will also ask a number of questions as it processes the packages and the packages themselves may also ask several questions. Before each question there is usually a description of what it is asking and the questions are too varied to discuss completely here. |