In addition to programs and their associated data files, Debian packages contain control data that
enable the package management tools to support advanced features:
A main control file contains version and package interrelationship data. The version
can be compared to an installed version of the same package to determine whether an
upgrade is needed. The interrelationship data tell the package management tools which
packages must or cannot be installed at the same time as the package.
Package interrelationship fields include Depends, Conflicts, Replaces, Provides,
Recommends, Suggests, and Enhances. For a complete list of control file fields, see
http://debian.org/doc/debian-policy/ch-controlfields.html.
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Choosing and Installing a Linux Distribution Part III
Optional preinst, postinst, prerm, and postrm files can instruct the package
management tools to perform functions before or after package installation or removal.
For example, most packages containing daemons (such as Apache HTTPD) include a
postinst script that starts the daemon automatically after installation.
A conffiles file can designate specific files in the package as configuration files, which
are not automatically overwritten during upgrades. By default, all files under the /etc/
directory are configuration files.
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