Fix machine-id workaround to also work on first boot #242
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To make this work, we have to do two things: 1. Run the systemd-machine-id-commit service only on first boot systemd-machine-id-commit does its job just fine if the file contains “uninitialized”, even if it's bind mounted from persistent storage. It only misbehaves if the file contains an actual machine-id, since it then thinks it needs to be committed. This can be worked around by only running the service on the first boot. 2. Create the machine-id file with the string “uninitialized” in it Our standard handling of non-existent files is to create a symlink, but this makes systemd behave a bit strangely. It follows the symlink and creates the “uninitialized” machine-id at the linked location. Then it bind mounts a newly generated machine-id over the file in persistent storage. This works, but it seems to confuse systemd-machine-id-commit since the file is not actually a bind mount over /etc/machine-id, so the machine-id will not be committed on this boot cycle and will still contain “uninitialized” on the next boot. This makes the next boot also recognized as the “first boot”. This time, however, systemd-machine-id-commit does its job, since the file is a bind mount to persistent storage. The workaround for this, is to just skip the symlinking step and go straight to bind mounting. However, since the file needs to exist to be bind mounted, we also have to create it with the string “uninitialized” as its contents.
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To make this work, we have to do two things:
Run the
systemd-machine-id-commitservice only on first bootsystemd-machine-id-commitdoes its job just fine if the file containsuninitialized, even if it's bind mounted from persistent storage. It only misbehaves if the file contains an actual machine-id, since it then thinks it needs to be committed.This can be worked around by only running the service on the first boot.
Create the machine-id file with the string
uninitializedin itOur standard handling of non-existent files is to create a symlink, but this makes systemd behave a bit strangely. It follows the symlink and creates the
uninitializedmachine-id at the linked location. Then it bind mounts a newly generated machine-id over the file in persistent storage. This works, but it seems to confusesystemd-machine-id-commitsince the file is not actually a bind mount over /etc/machine-id, so the machine-id will not be committed on this boot cycle and will still containuninitializedon the next boot. This makes the next boot also recognized as the “first boot”. This time, however,systemd-machine-id-commitdoes its job, since the file is a bind mount to persistent storage.The workaround for this is to just skip the symlinking step and go straight to bind mounting. However, since the file needs to exist to be bind mounted, we also have to create it with the string
uninitializedas its contents.