9afd5e7b97
There is no technical reason to support systems with split-usr, except for backwards compatibility. Even though systemd itself makes an effort to support this, many other tools aren't as careful. Despite those efforts, we (collectively) get it wrong often, because doing it "wrong" on systems with merged-usr has no consequences. Since almost all developers are on such systems, any issues are only discovered late. Supporting this split-usr mode makes both code and documentation more complicated. The split is purely artificial and has no justification except to allow old installation to not update. Mechanisms to update existing systems are available though: Fedora did that in https://fedoraproject.org/wiki/Features/UsrMove, Debian has the usrmerge package. The next version of Debian will only support systems with split-usr=false, https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=978636#178: The Technical Committee resolves that Debian 'bookworm' should support only the merged-usr root filesystem layout, dropping support for the non-merged-usr layout. Let's start warning if split-usr mode is used, in preparation to removing the split in one of the future releases.
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