View source for APT and aptitude

==Using APT and Aptitude==

Your Debian system can easily be expanded, and also kept up-to-date with the latest security fixes, if you use Debian's beautiful [http://www.debian.org/doc/manuals/apt-howto/ch1.en.html APT (Advanced Packaging Technology)] tools. Of all available [http://en.wikipedia.org/wiki/Advanced_Packaging_Tool APT-based tools], we usually use the following:
* apt-get, the command line utilities that go with APT; or
* aptitude, a [http://en.wikipedia.org/wiki/Curses_%28programming_library%29 curses-based] frontend for APT.

These APT-based tools are incredibly powerful and flexible, but we're not going to explain them fully here (for tuturials and whatnot, go [http://www.debian.org/doc/manuals/apt-howto/ here]). What we need to establish now, is how to configure APT, and how to use it.

APT gets its information from a configuration file that can be found in ''/etc/apt''. Of these, the most important is ''sources.list'' because it defines what packages and updates can be installed from where, and even what version of Debian we want to maintain. For now let's just suffice to say that in the sources.list, you need to remove the references to the CD-ROm with which you installed the system, and specify which on-line repository you wish to use for installing and updating packages. To this end, open ''/etc/apt/sources.list'' with [[Vim | your favourite text editor]] while you are logged in as root.

References to the CD-ROM look a bit like this:
 deb cdrom:[Debian GNU/Linux testing _Etch_ - Official Beta i386 CD Binary-1 20070317-21:45]/ etch contrib main
Disable this line by putting a hash (#) in front of it (you could have more than one line beginning with ''deb cdrom:'').

Now make sure you have a section that references one or more on-line repositories. This could make your ''sources.list'' look like this:
<pre>
# deb cdrom:[Debian GNU/Linux testing _Etch_ - Official Beta i386 CD Binary-1 20070317-21:45]/ etch contrib main

deb ftp://ftp.nl.debian.org/debian/ etch main contrib
deb-src ftp://ftp.nl.debian.org/debian/ etch main contrib

deb http://security.debian.org/ etch/updates main contrib
deb-src http://security.debian.org/ etch/updates main contrib

# deb ftp://ftp.nl.debian.org/debian-volatile etch/volatile main contrib

</pre>

When you want to update, change, add software, or even remove software, you better update your APT system by running one of the following commands:
* sudo apt-get update
* sudo aptitude update
* sudo aptitude, then press ''u''
Note: if you haven't installed [[sudo]] yet, then you can only run the commands as root, and they are then: ''apt-get update'', ''aptitude update'', and ''aptitude'' then ''u''.

==Getting informed on installed packages==
You might at some time wonder if a package is already installed. Usually, you'd check this using
 dpkg --get-selections
The output of this can be rather unwieldy, but you can send the output to a program like ''grep'' to refine your search. As an example: use
 dpkg --get-selections | grep install -c
to see just how many packages you have.

But this standard command doesn't directly concerns itself with versions or installation history.

Now if you're wondering what version a specific package (or set of packages) is, then you can install package ''apt-show-versions'' and run it on the command line; if you wish to know the version of a particular file, e.g. ''sudo'', you'd run
 apt-show-versions sudo
This package is described on [http://www.debianadmin.com/list-your-installed-package-versions-with-apt-show-versions.html Debian Admin]. It can do much more, but there's a fine ''man'' page for that.

Furthermore, if you're interested in the installation history of your packages, you could check out the ''dpkg'' log file, by default ''/var/log/dpkg.log''. This logging file/location is set in ''/etc/dpkg/dpkg.cfg''. So to find the installation time/date of all programs, you could execute
 grep "status installed" /var/log/dpkg.log

==Getting information on packages that are NOT installed==
This can be done with a package named '''apt-file'''. More information [http://www.debianhelp.co.uk/findfile.htm here].