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

[Alessandro Tagliapietra]

Thanks for helping Mantas,

What I saw is:
 - before first boot /etc/machine-id is empty (and I think that's expected)
 - right after boot, /etc/machine-id isn't writable because the root fs is
mounted as readonly from fstab
 - after the /etc overlay is mounted /etc/machine-id should still be the
one from the underlying filesystem and at this point is also writable,
however it's still empty

During boot I see:

[    3.577477] systemd[1]: Initializing machine ID from random generator.
[    3.584284] systemd[1]: Installed transient /etc/machine-id file.

however /etc/machine-id shouldn't be writable at that point, what should I
do? Make our overlay mount unit depend on whatever service is generating
machine-id and make sure our mount happens before the generation of
machine-id?

Thanks

--
Alessandro Tagliapietra


On Tue, Jun 1, 2021 at 12:13 AM Mantas Mikulėnas <grawity at gmail.com> wrote:

> On Tue, Jun 1, 2021 at 10:07 AM Alessandro Tagliapietra <
> tagliapietra.alessandro at gmail.com> wrote:
>
>> 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
>>
>
> My guess is that it's related to /etc/machine-id somehow becoming
> inaccessible, since networkd's DUID-EN (DUIDType=vendor) is based on that.
>
> --
> Mantas Mikulėnas
>
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