Debian installs its software in the form of .deb files. These .deb files contain software, configuration files, documentation, and dependency information.
First, well get some of the common terminology taken care of, then well discuss package management using apt-get, and finally, package management using deb files.
Packages
Packages in this case refers to software in the form of .deb bundles. Packages contain compressed archives with files, documentation, management scripts, and dependency information.
Sources
Sources refer to a location containing software packages. Apt-get uses software repository locations to automatically install the correct package or series of packages.
Dependencies
Dependencies refer to libraries or other pieces of software necessary for any given software to run. For example, you want to install somepackage-0.123-4.i386.deb. In order for this software to install, any software that it needs to run will need to be installed either automatically through apt-get or by manually installing a .deb file.
Package Naming Conventions
Proper deb packages adhere to a standard naming convention. The name may seem a bit long, but knowing how to identify a package based on its naming convention helps considerably when trying to find the correct software. Packages are usually referred to using the following naming convention, in this example were using the package "screen"
packagename_version_architecture.deb
in our example, the package "screen" is
screen_4.0.3-0.3+b1_i386.deb
Working with Debian Packages
There are two main considerations for package management in Debian: dpkg and apt. The dpkg command is used to manipulate (create, query, install, etc) .deb packages. The apt command set allows you to install packages from remote sources, whereas dpkg is used on .deb files that are already downloaded to your system. The best way to think about apt versus dpkg is that apt extends dpkg so that if a package requires dependencies, apt will attempt to fetch and install them in order to install the requested package. Here I will show you some examples of common package management in Debian:
First update your apt-cache sources
apt-get update
Update all available pacakages on your system
apt-get upgrade
To install a pacakge, in this case screen
apt-get install screen
To remove screen but keep its configuration files
apt-get remove screen
To completely remove screen including its configuration files
apt-get --purge remove screen
To list all pacakages installed on a system
dpkg -l
To list the current version of a particular pacakge on a system, in this case screen
dpkg -l | grep screen
To search for pacakages that match a description, in this case nids
apt-cache search nids
To show general information about a package, in this case "harden-nids"
apt-cache showpkg harden-nids
To install a .deb file already downloaded to your server
dpkg -i package.deb
To remove a .deb file
dpkg -r package.deb
To remove all leftover .deb files after updates/upgrades
apt-get autoclean
For more information on Debian package management check the Debian FAQ - Basics of Debian package management system
