Querying the package list with apt-cache
Look Inside
We take a look at apt-cache, an essential utility for command line-based package management.
Debian-based systems have several dozen utilities for managing packages from the command line. After apt-get and dpkg, the most important is apt-cache [1]. Apt-cache queries the packages in your repositories, providing the information you want before you install. If you want to know a package's statistics and dependencies, which package contains an application, or whether a package exists at all, then apt-cache is an essential utility for command line-based package management.
The cache referred to in the name is the list of information about all packages available in the Debian package management system – which means those installed from tarballs are excluded. This cache is based on the sources contained in /etc/apt/source.lists, as well as some files in the /etc/apt/sources.lists.d directory.
The main part of the cache, which contains information about the current state of each package, is stored in /var/lib/apt/lists. Information about packages in transition, such as those held back during installation, is stored in /var/lib/apt/lists/partial/. As you might guess from the locations, regular users can query apt-cache, but any alteration or updating of the cache requires the root account.
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