Why does Debian change software?

Summary

When I wrote Why is Debian the way it is?, a year and a half ago, I was asked to also cover why Debian changes the software it packages. Here’s a brief list of examples of why that happens: Software in Debian needs to follow certain policies as set by Debian over the years, and documented in the Debian Policy Manual. These are mostly mundane things like system wide configuration being in /etc, documentation in /usr/share/doc, and so on. Some of this is more intricate, like when names of executables can be the same in different packages. Programs included in Debian need to work together in other ways. This might mean require changing one or both. As an example, they might need to agree where Unix domain socket exists, or what Unix user account they should run under. Debian will remove code that “calls home” or tries to update software in a way that bypasses the Debian packaging system. This is done both for privacy reasons, and because updating software without going via the packaging system is usually problematic from a functional point of view, and always problematic from a security point of view. Debian may fix bugs before they’re fixed in upstream, or may backport a bug fix to an earlier version. The goal here is to make life better for users of Debian. Debian does this especially for fixes to security problems, but also for other problems. Debian avoids including anything in the main part of its package archive it can’t legally distribute. This applies to the source packages. This means, Debian may strip out those parts software that it doesn’t think are free according to the Debian Free Software Guidelines. The stripped-out parts might be moved to another package in the “non-free” part of Debian. An example might a manual that is licensed under the GNU Free Documentation License with immutable parts, or a logo that can’t be changed. Debian has often added a manual page when the upstream doesn’t provide one. Thank you to Jonathan McDowell for help with this list...