Ubuntu's package management
system is derived from the same system used by the Debian GNU/Linux
distribution. The package files contain all of the necessary files, meta-data,
and instructions to implement a particular functionality or software
application on your Ubuntu computer.
Debian package files
typically have the extension '.deb', and usually exist in repositories which
are collections of packages found on various media, such as CD-ROM discs, or
online. Packages are normally in a pre-compiled binary format; thus
installation is quick, and requires no compiling of software.
Many complex packages use
the concept of dependencies. Dependencies are additional packages required
by the principal package in order to function properly. For example, the speech
synthesis package festival depends upon the package libasound2,
which is a package supplying the ALSAsound library needed for audio
playback. In order for festival to function, it and all of its
dependencies must be installed. The software management tools in Ubuntu will do
this automatically.
dpkg
dpkg is a
package manager for Debian-based systems. It can install, remove, and
build packages, but unlike other package management systems, it cannot
automatically download and install packages or their dependencies. This section
covers using dpkg to manage locally installed packages:
To list all packages installed on the system,
from a terminal prompt type:
dpkg -l
Depending
on the amount of packages on your system, this can generate a large amount of
output. Pipe the output through grep to see if a specific package is
installed:
dpkg -l | grep apache2
Replace apache2 with
any package name, part of a package name, or other regular expression.
To list the files installed by a package, in
this case the ufw package, enter:
dpkg -L ufw
If
you are not sure which package installed a file, dpkg -S may be able
to tell you. For example:
dpkg -S /etc/host.conf
base-files: /etc/host.conf
The
output shows that the /etc/host.conf belongs to the base-files package.
You can
install a local .deb file by entering:
sudo dpkg -i zip_3.0-4_i386.deb
Change zip_3.0-4_i386.deb to
the actual file name of the local .deb file you wish to install.
Uninstalling a package can be
accomplished by:
sudo dpkg -r zip