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APT User's Guide
Chapter 2 apt-get

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. For instance,

     # apt-get update
     Get http://ftp.de.debian.org/debian-non-US/ stable/binary-i386/ Packages
     Get http://llug.sep.bnl.gov/debian/ frozen/contrib Packages
     Reading Package Lists... Done
     Building Dependency Tree... Done

Once updated there are several commands that can be used:

upgrade

Upgrade will attempt to gently upgrade the whole system. Upgrade will never install a new package or remove an existing package, nor will it ever upgrade a package that might cause some other package to break. This can be used daily to relatively safely upgrade the system. Upgrade will list all of the packages that it could not upgrade, this usually means that they depend on new packages or conflict with some other package. dselect or apt-get install can be used to force these packages to install.

install

Install is used to install packages by name. The package is automatically fetched and installed. This can be useful if you already know the name of the package to install and do not want to go into a GUI to select it. Any number of packages may be passed to install, they will all be fetched. Install automatically attempts to resolve dependency problems with the listed packages and will print a summary and ask for confirmation if anything other than its arguments are changed.

dist-upgrade

Dist-upgrade is a complete upgrader designed to simplify upgrading between releases of Debian. It uses a sophisticated algorithm to determine the best set of packages to install, upgrade and remove to get as much of the system to the newest release. In some situations it may be desired to use dist-upgrade rather than spend the time manually resolving dependencies in dselect. Once dist-upgrade has completed then dselect can be used to install any packages that may have been left out.

It is important to closely look at what dist-upgrade is going to do, its decisions may sometimes be quite surprising.

apt-get has several command line options that are detailed in its man page, apt-get(8). The most useful option is -d which does not install the fetched files. If the system has to download a large number of package it would be undesired to start installing them in case something goes wrong. When -d is used the downloaded archives can be installed by simply running the command that caused them to be downloaded again without -d.