Bug: machine id is never generated

["Moessbauer, Felix" <felix.moessbauer@siemens.com>]

Hi,

when booting plain ISAR images (with Debian11), the "/etc/machine-id" is never generated.
This breaks a couple of services that depend on having the id.
An example is the systemd-networkd with DHCP, leading to error messages like this one (and breaking networking):

systemd-networkd[277]: enp8s0: DHCP6 CLIENT: Failed to set identifier: No such file or directory

The error can manually be fixed by running "systemd-machine-id-setup", but this obviously does not work in embedded scenarios.

The root cause could be that /etc is read-only mounted when the first-boot-complete.target is reached.
At least the logs indicate this:

journalctl --grep machine --no-pager
-- Journal begins at Thu 2022-07-21 15:07:21 UTC, ends at Thu 2022-07-21 15:35:20 UTC. --
Jul 21 15:07:21 test-image systemd[1]: System cannot boot: Missing /etc/machine-id and /etc is mounted read-only.
Jul 21 15:07:21 test-image systemd[1]: 1) /etc/machine-id exists and is populated.
Jul 21 15:07:21 test-image systemd[1]: 2) /etc/machine-id exists and is empty.
Jul 21 15:07:21 test-image systemd[1]: 3) /etc/machine-id is missing and /etc is writable.
Jul 21 15:07:24 test-image systemd[1]: Condition check resulted in Commit a transient machine-id on disk being skipped.

Maybe Quirin knows more, as he implemented the postproc removal in 8b5e3f9.
IIRC Jan also mentioned something that "rw" has to be added to the kernel cmdline, but this looks like a workaround as well.
For the sake of completeness:

cat /proc/cmdline
initrd=\initrd.img-5.10.0-16-amd64 LABEL=Boot root=PARTUUID=9ad286e9-8df8-42c2-ac7d-0f2d7387d03d rootwait console=tty0 console=ttyS0,115200

IMO this is a pretty critical bug as it affects a ton of images.

Best regards,
Felix

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