logind needs access to /run/user/, udevd fails during early boot
with these settings
BusName=org.freedesktop.login1
CapabilityBoundingSet=CAP_SYS_ADMIN CAP_AUDIT_CONTROL CAP_CHOWN CAP_KILL CAP_DAC_READ_SEARCH CAP_DAC_OVERRIDE CAP_FOWNER CAP_SYS_TTY_CONFIG
WatchdogSec=1min
-ReadOnlySystem=yes
-ProtectedHome=yes
# Increase the default a bit in order to allow many simultaneous
# logins since we keep one fd open per session.
RestartSec=0
ExecStart=@rootlibexecdir@/systemd-udevd
MountFlags=slave
-ReadOnlySystem=yes
-ProtectedHome=yes