Pre-released updates ON by default

[Oliver B]

When installing a fresh Ubuntu 20.04 from an USB Stick, then in the "Software & Updates" settings window, where there is a possibility to set up software sources, on the "Developer Options" tab the "Pre-released updates (focal-proposed)" checkbox is ON by default, therefore installing pre-release packages for regular users as well.
And not just when booting from the installation media (USB stick), but after installing the system onto the main HDD / SSD , the situation is the same.

The issue popped up when I already had gnome-shell 3.36.2 on my system (completely killing gnome-tweaks), while the latest stable release was just 3.36.1

Thanks to #ubuntu IRC channel and especially "ioria" user to help me figuring out what is going on.

The installation ISO image I was used has the signature from 3rd May.

$cat /var/log/installer/media-info
Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200503)
$lsb_release -rd
Description: Ubuntu 20.04 LTS
Release: 20.04
$uname -a
Linux sarmx777 5.4.0-31-generic #35-Ubuntu SMP Thu May 7 20:20:34 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
$

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubiquity (not installed)
ProcVersionSignature: Ubuntu 5.4.0-31.35-generic 5.4.34
Uname: Linux 5.4.0-31-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Mon May 18 20:06:44 2020
InstallCmdLine: file=/cdrom/preseed/ubuntu.seed initrd=/casper/initrd quiet splash --- maybe-ubiquity
InstallationDate: Installed on 2020-05-11 (7 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200503)
SourcePackage: ubiquity
Symptom: installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Paul White (paulw2u)]

https://wiki.ubuntu.com/PointReleaseProcess suggests that building images with -proposed enabled is a deliberate action for LTS point releases unless building images less than a week before the actual point release (if I've read everything correctly - the last eight lines are important).

So not a bug although I'm still unclear why the decision to enable -proposed has been made unless it's simply to install updates that are intentionally not promoted from -proposed until the point release is made final, e.g. HWE stack.

[Steve Langasek (vorlon)]

> The installation ISO image I was used has the signature from 3rd May.

So that is not the Ubuntu 20.04 image, that is a daily test image that exists for preparation of the next point release.

The images have -proposed enabled for the express purpose of ensuring we produce media that can be used for testing new versions of the installer for SRU before they are released to -updates.

But this is not the image that you should be downloading and using to install unless you are doing testing for the point releases.