[systemd-devel] DHCP6 client failing when /etc is mounted as overlayfs

[Alessandro Tagliapietra]

Hello everyone,

I'm using yocto to create a custom linux image for a raspberry pi.
We have an "agent" that writes /etc/systemd/network/20-eth.network when the
final user wants to have a static IP address and we remove the file when
they switch back to DHCP.

After creating/deleting the file above we run `networkctl reload &&
networkctl reconfigure eth0`.
We mount the overlayfs with a custom .mount unit.

We've noticed that DHCP works fine if systemd-networkd starts before we
mount the overlayfs but it doesn't if systemd-networkd is
restarted/reconfigured after the folder is mounted or started after the
overlay .mount unit.

Every interface DHCP fails with:

DHCPv6 CLIENT: Failed to set DUID-EN: No medium found
eth0: DHCP6 CLIENT: Failed to set DUID: No medium found

We're using systemd 246 (246.9+) and we're planning on upgrading to 247.6
soon.
Is this expected? Is it somehow incompatible with overlayfs?
Or maybe it's not related to the /etc filesystem and it's something else?

Any help is really appreciated.

Thanks

--
Alessandro Tagliapietra
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