Debian 15

We will now go into how to add, remove, and maintain programs. The package system supports multiple package sources (CDs, DVDs, File System, HTTP, FTP). Applications like apt-get and aptitude automatically resolves dependencies. They also maintain a package repository database of all installed packages.
Applications to manage programs include dpkg*, apt-* and aptitude. Apt-get is a front-end to dpkg, and it is not interactive. On the other hand, aptitude is interactive.

You can list the packages installed on the system through dpkg:
dpkg -l

Typically, the output of dpkg -l is piped into grep to selectively show lines of interest.

To list the package a file came from, use:
dpkg -S filename

To see a package's status:
dpkg -s openssh-client

To display a list of files included in the package:
dpkg -L openssh-client

To install a package:
dpkg -i package1.deb [package2.deb...]

To uninstall a package:
dpkg -r package1 package2

In this example, we will install tofrodos, which converts a text file to and fro DOS format. In DOS systems, each line terminates with a CR/LF, but in Unix, lines terminate with LF. todos can replace all LF with CR/LF.

First, browse to debian.org. Click on Debian Packages, then search for "tofrodos". Download the tofrodos .deb package for your arthitecture.

Now, browse to the folder containing the file in a terminal, and use dpkg -i tofrodos... to install the package.

After installing, you can check if it's successfully installed through:
dpkg -l | grep tofrodos
dpkg -s tofrodos

A typical file name would look like:
tofrodos_1.7.8.debian.1-1_i386.deb

The package name is tofrodos.
The version is 1.7.8.debian.1-1 (Major, Minor, Patch Release/Build)
The platform is i386
Package suffix is .deb

To use tofrodos to convert from *nix to DOS:
todos test.txt

After doing so, verify the file through:
file test.txt

To uninstall tofrodos, use:
dpkg -r tofrodos

The apt-get is a front-end to dpkg. It provides all features of dpkg, and also maintains a configuration file which contains package sources. The sources of apt-get is stored in /etc/apt/sources.list.

Package sources are arranged in the following categories:
1) Main - Free programs included with the production build of Debian
2) Contrib - Free programs that rely upon Non-Free programs
3) Non-free - Non-Free programs only

Free in this case represents not only the cost of the program, but also the availability of the source code (e.g. open-source).

By default, configuration settings of a program isn't removed when it is uninstalled through apt-get or aptitude. To clear those configurations (in /etc), use:
apt-get purge

To add a CDs/DVDs source, use:
apt-cdrom add

To install tofrodos using apt, use:
apt-get install tofrodos

To uninstall a package, use:
apt-get remove tofrodos

In Aptitude, you can search for packages through '/'. Aptitude tallies tasks (install/remove), then execute them sequentially. Aptitude trees are rearranged in the following manner:
-Node (Installed/Not-Installed etc.)
--Package Group (Administrative, Communication, etc.)
---Branch of Package (Main, Contrib, Non-Free)

Use the tasks node in Aptitude to install common classes of software, e.g. (Desktop Environment, Laptop, Server, etc).

Use + and - to add and remove packages from queue. Next, press 'g' to see the queue, and 'g' again to execute. Bolded packages are installed.