The upstream unit has ConditionPathIsReadWrite=/etc, which is always
false on the read-only overlay, so the previous commit alone requires
users that want persistence to override the conditions themselves before
the generated ID can be written back.
Use ConditionFirstBoot instead, with the empty placeholder
first-boot is "no" and commit stays skipped, but when a writable
file containing "uninitialized" is bind-mounted over /etc/machine-id,
first-boot is "yes" once and commit writes the ID through the bind.
r-vdp
86a665d5b6