APT, through the apt-get utility, maintains a database of packages
available in the repositories that it is configured to check and can handle automatically
downloading new or upgraded packages. A program named aptitude has been added to simplify
package management, and it acts as an interface for the command line operations of apt-get.
When installing or upgrading packages, APT downloads the necessary files to a local cache directory
and then instructs the dpkg tool to take the appropriate actions. Among other things, this allows
the user to select programs for addition or removal without having to manually instruct the system
to handle any package dependencies.
Most basic package management functions are performed by dpkg, although not always at the
direct request of the user. This tool handles medium-level package installation and removal, and
also manages the package status database. That database contains information about every package
known to dpkg, including the package meta information and two other important fields: the package
state and selection state.
NOTE
305
Running Debian GNU/Linux 9
More information about how to determine the state of a package can be found in the
???Querying the Package Database??? section of this chapter.
As its name suggests, the package state indicates the present state of the package, which is one of
the following:
not-installed??”The package is known but is not installed on the system.
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