[Original Description]
In Ubuntu the GUI for upgrading packages is update-manager allowing debconf questions to be answered when needed and Ubuntu also offers unattended-upgrades for upgrading packages in the background and it keeps back packages from upgrading when configuration-file changes would need user interaction during the upgrade. Unattended-upgrades can be configured to perform upgrades during system shutdown.
Gnome Software in Bionic started offering performing upgrades during shutdown using PackageKit independently from update-manager and unattended-upgrades without offering all of the features of either one.
Unless there is a decision to fully switch to Gnome Software I suggest disabling the "Install pending software updates" on the shutdown screen to avoid confusing users.
[Impact]
As stated in the original description, users may be confused by the checkbox on the shutdown dialog offering to install updates, considering that all updates in Ubuntu are currently handled by a separate GUI (update-manager).
This is fixed in cosmic (3.29.1-0ubuntu6) by disabling offline updates in the packagekit refresh plugin.
The fix is trivial and complements an existing patch that was already disabling updates in gnome-software.
[Test Case]
0) Prerequisite: a bionic system not fully up-to-date (if yours is fully up-to-date, downgrade a package)
1) Verify that the following file doesn't exist (if it does, remove it): /var/lib/PackageKit/prepared-update
2) Open gnome-software
3) Click on the "Updates" tab, and click the refresh button in the top-left corner
4) Wait for the refresh operation to be complete (gnome-software might incorrectly report that there are no updates available, this is a separate issue, bug #1709725)
5) Wait a minute or two to ensure there are no pending packagekit async tasks
6) Verify that /var/lib/PackageKit/prepared-update still doesn't exist, and consequently, when requesting to shut down the computer, the shutdown dialog doesn't offer a "Install pending software updates" checkbox
[Regression Potential]
gnome-software is not used to install updates (from the archive) on Ubuntu. However firmware updates and updates from other packaging systems (such as flatpak) should still appear in the updates tab, when available.
[Other Info]
The updates tab in gnome-software may claim that there are no updates available, when in fact there are. This is also confusing, but is a separate issue (bug #1709725) and will be addressed separately.
Thank you for your bug report. What you describe is a bug, we don't have that behaviour/dialog enabled by default. Do you have any non standard packagekit packages/
Does it leads to any problem or just to UI confusion? (I saw dialog a few times during the bionic cycle but checking the box didn't seem to do anything)