Debian-based systems are full of obscure packages and procedures. Users can run a Debian-based system for years and still be surprised by some of its features, especially if they are not developers. Yet these obscure features can sometimes be as helpful to ordinary users as anyone else. Diffoscope, for example, is intended as a tool for overseeing long-term support for official releases, but its support for binary files allows writers to fully take advantage of git, while debfoster and deborphan both assist in writing scripts for packages and in freeing up disk space by identifying unnecessary packages. Another case in point is the Debian alternatives system [1], which is used in package scripts such as postinst, prerm, and postrm, but it can also automate user interaction with over 120 applications through the update-alternatives command, potentially defining the choice of everything from text editors and web browsers to MP3 decoders and desktop wallpaper.

Unknown to many users, update-alternatives is installed by default on Debian-based systems. A fork also exists on Fedora-based systems [2], including Red Hat Enterprise Linux. The update-alternatives command is intended to manage packages with similar or duplicate functionality under a category or link group. This arrangement is useful because, like many distributions, Debian values freedom of choice. With 59,000 packages at last count [3], there can be numerous applications whose functionality is identical or overlaps. For example, Vim's variants include Elvis, Neovim, vim-tiny, and vim-nox, plus at least half a dozen others. Given many Linux users' fondness for constantly exploring applications, the older a system is, the more likely any set of variants is installed. Although Wayland has yet to be supported by update-alternatives, there are still dozens of link groups that make it a useful tool.

Roughly equivalent to the choice of default applications in many desktop environments, update-alternatives's main difference in functionality is that it can set which other applications a running application opens. For example, the crontab command uses the -e option to choose an editor in which to edit the command. Ordinarily, using -e opens a screen that lists available editors. By contrast, if a user's default editor is set with update-alternatives, this extra screen is skipped. You could get the same result by setting an editor as an environmental variable, but by using update-alternatives, you can maintain a list of choices and can change the default with a quick command. Note that on Debian and possibly some derivatives, you may need to change permissions on the command and its files to enable it.

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