After upgrading from systemd-233 to systemd-236, my software raid stopped working on boot. I eventually tracked down the problem to udev. Since systemd moved from /usr/lib to /lib, it only looks for udev files in /lib/udev/rules.d . Any files installed in /usr/lib/udev/rules.d by other packages (e.g. mdadm, libinput) are still in the old /usr/lib/udev/rules.d directory, and systemd/udev doesn't read them. The files in /usr/lib/udev/rules.d need to be (1) mv'd manually to /lib/udev/rules.d, (2) symlinked manually to /lib/udev/rules.d, or (3) the packages that installed the files need to be re-emerged. emerge -1 /usr/lib/udev/rules.d/* works just fine. Maybe these instructions should be added to the 2017-07-16-systemd-rootprefix news item? Reproducible: Always
Gentoo's systemd hasn't used /usr/lib/udev for several years and have been then it was only enabled for a few months. We were doing some weird stuff with pkg-config before 234, which probably caused your install to remain under /usr.
