Comment 27 for bug 1888916

I tested a release upgrade from Bionic to Focal and confirm that my sources.list file was not reverted back to Artful.

bdmurray@clean-bionic-amd64:/tmp/20.04$ head /var/log/dist-upgrade/main.log
2020-08-31 08:01:42,527 INFO Using config files '['./DistUpgrade.cfg.bionic']'
2020-08-31 08:01:42,527 INFO uname information: 'Linux clean-bionic-amd64 5.4.0-42-generic #46~18.04.1-Ubuntu SMP Fri Jul 10 07:21:24 UTC 2020 x86_64'
2020-08-31 08:01:42,819 INFO apt version: '1.6.12ubuntu0.1'
2020-08-31 08:01:42,820 INFO python version: '3.6.9 (default, Jul 17 2020, 12:50:27)
[GCC 8.4.0]'
2020-08-31 08:01:42,822 INFO release-upgrader version '20.04.25' started

bdmurray@clean-bionic-amd64:/tmp/20.04$ grep -A12 "no entry" /var/log/dist-upgrade/screenlog.0
While scanning your repository information no entry about bionic
could be found.

An upgrade might not succeed.

Do you want to continue anyway?

Continue [yN] n

Restoring original system state

Aborting
Reading package lists... Done

bdmurray@clean-bionic-amd64:/tmp/20.04$ cat /etc/apt/sources.list
deb http://192.168.10.7/ubuntu focal main restricted universe multiverse
deb http://192.168.10.7/ubuntu focal-updates main restricted universe multiverse
#deb http://192.168.10.7/ubuntu focal-proposed main restricted universe multiverse
deb http://192.168.10.7/ubuntu focal-security main restricted universe multiverse
deb-src http://192.168.10.7/ubuntu focal main restricted universe multiverse
deb-src http://192.168.10.7/ubuntu focal-updates main restricted universe multiverse
#deb-src http://192.168.10.7/ubuntu focal-proposed main restricted universe multiverse
deb-src http://192.168.10.7/ubuntu focal-security main restricted universe multiverse

Keep in mind the sources.list file is correct as the test case had you modify it to the release which you are upgrading.

bdmurray@clean-bionic-amd64:/tmp/20.04$ md5sum /etc/apt/sources.list
6d4439d7fd3f142f81b70e00abd7b95a /etc/apt/sources.list
bdmurray@clean-bionic-amd64:/tmp/20.04$ md5sum /etc/apt/sources.list.distUpgrade
6d4439d7fd3f142f81b70e00abd7b95a /etc/apt/sources.list.distUpgrade