This is supposed to play the same roles /var/lib/dbus/machine-id,
however fixes a couple of problems:
- It is available during early boot since it is stored in /etc
- Removes the ID from the D-Bus context and moves it into a system
context, thus hopefully lowering hesitation by people to use it.
- It is generated at installation time. If the file is empty at boot
time it will be mounted over with a randomly generated ID, which is
not saved to disk. This is useful to support state-less machines with
no transient or writable /etc configuration.
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