Hi Simon, Well, it's easy to find the answer if you look at the mentioned upstream commit. It's a workaround for the notorious bug [1] which upstream systemd developers still refuse to fix. True, there was some patch in systemd 204, but since then a lot of versions passed by, and it seems that the latest systemd versions still set XDG_RUNTIME_DIR to the wrong value sometimes. The most known consequence of it is the impact on dconf, which makes various user-level software behave wrong (e.g. eat 100% CPU or a lot of memory, freeze completely, etc.) [2][3][4][5][6].
[1] https://bugzilla.redhat.com/show_bug.cgi?id=753882 [2] https://bugs.debian.org/732209 [3] https://bugs.debian.org/766464 [4] https://bugs.debian.org/767173 [5] https://bugs.debian.org/769889 [6] https://bugs.debian.org/772910
