live server depends on arguably buggy systemd-networkd behaviour to avoid slow boot

[Michael Hudson-Doyle]

[Impact]
If there default network configuration does not actually get a server online, the live server installer only avoids a long delay by dint of relying on some dubious behaviour of networkd: if all interfaces are marked optional: true, systemd-networkd-wait-online does not wait. If we want to fix this bug so that systemd-networkd-wait-online.service means the machine is actually online, then the live server installers boot will be slow.

The fix, already present in cosmic, is to just symlink systemd-networkd-wait-online to /bin/true.

[Test plan]
Boot the live server installer in a VM with no NICs, or with nics that do not have an answering dhcp.

[Regression potential]
As the boot behaviour is not changed (i.e. boot is not delayed even if there is no network) there should be no subtle regressions once the basic bits have been verified to work.

[Łukasz Zemczak (sil2100)]

Hello Michael, or anyone else affected,

Accepted livecd-rootfs into bionic-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/livecd-rootfs/2.525.1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-bionic to verification-done-bionic. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-bionic. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Michael Hudson-Doyle (mwhudson)]

I verified the fix in bionic-proposed by the following steps:

1) Copied-with-binaries livecd-rootfs 2.525.1 from bionic-proposed to an otherwise empty PPA
2) Waited for publication
3) Kicked off a live-server livefs build (https://launchpad.net/~mwhudson/+livefs/ubuntu/bionic/live-server-test/+build/133986)
4) Verified that this build used livecd-rootfs 2.525.1 by reading the log
5) Downloaded the installer.squashfs from the build and injected it into the latest bionic live-server daily
6) Booted the ISO in VM a few setups:
 a) With working networking via DHCP
 b) With no NIC
 c) With a NIC but no DHCP

In all situations the boot was as normal and systemd-networkd-wait-online was very low down in "systemd-analyze blame" output

[Launchpad Janitor (janitor)]

This bug was fixed in the package livecd-rootfs - 2.525.1

---------------
livecd-rootfs (2.525.1) bionic; urgency=medium

  * Symlink systemd-networkd-wait-online to /bin/true in the live installer
    live session to avoid depending on buggy systemd behaviour. (LP: #1773719)
  * Remove "optional: true" from installer netplan config.

 -- Michael Hudson-Doyle <email address hidden> Wed, 23 May 2018 14:27:01 +1200

[Łukasz Zemczak (sil2100)]

The verification of the Stable Release Update for livecd-rootfs has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.