[answers.yaml] "Network: accept-default: yes" prevents the SnapList screen from appearing

[Paride Legovini]

This is a strange one :) When running a Focal preseeded install via answers.yaml, if a Network section like the following one is present:

Network:
  accept-default: yes

then the SnapList screen won't appear during the installation process, and the SnapList section of answers.yaml will be ignored. This is easy to reproduce: prepare an answers.yaml containing only the following:

Welcome:
  lang: en_US

Install accepting all the defaults and check how the SnapList screen appears normally. Then add:

Network:
  accept-default: yes

to the same answers.yaml and redo the installation in the same way. The SnapList screen won't appear anymore.

Attached are the installer logs for an installation where the SnapList failed to appear.

[Adding the "Welcome" section to the answers.yaml is a workaround for https://bugs.launchpad.net/subiquity/+bug/1864863]

[Paride Legovini (paride)]

This is preventing the ubuntu-focal-live-server-amd64-smoke-snap ISO testing job from succeeding.

[Paride Legovini (paride)]

This bug is still present as of the 20200324 images. I didn't tag it rls-ff-incoming as it doesn't seem to affect the normal, manual install process, however given that its root cause is not clear I think it's worth investigating to avoid surprises.

[Paride Legovini (paride)]

I think the problem here is that when the network config is preseeded with "accept-default: yes" subiquity does not wait enough time to get the network config from DHCP, and proceeds without network. This causes the snap installation to be skipped.

[Paride Legovini (paride)]

For some reasons with the latest ISO images the snap installation via answers.yaml switched from mostly failing to mostly succeeding (except on s390x, where it still mostly fails). This is racey and apparently something in the race changed, but it's still there.