Error message if installing Ubuntu 19.04 to pre-formatted partition

[Dave Rove]

The error message is generated if you format a partition before the installation, then install Ubuntu 19.04 to that partition _without_ requesting it be formatted during the installation.

The pop-up message is:

"Error restoring installed applications.

"An error occurred while restoring previously-installed applications. The installation will continue, but you may have to manually reinstall some applications after the computer reboots."

Hit OK on that, and a message says that the installation is complete, and the "restart now" button then boots the apparently undamaged Ubuntu 19.04 installation.

Steps to reproduce:

1. Before installation, format a hard-drive partition as ext4.
2. Begin installing Ubuntu (ubuntu-19.04-desktop-amd64.iso) from a flash drive.
3. At installer's "Installation type" step, select "Something else".
4. Select the previously formatted partition and set its mount point to "/".
5. Leave that partition's "format" box unchecked (the default).
6. Press "Install" and click through a warning about not formatting.
7. At the end of the installation, a popup says the installation has errors.

Presumably the error message is invoked because it assumes that if you do not request that the partition be formatted, then you are installing into a previous installation (i.e. upgrading) but something breaks at the end of the installation when it can find no evidence of said previous installation.

Formatting a partition _before_ the installation is useful for specifying specific file-system labels and UUIDs so that other operating systems installed on the same PC may mount the partition as they did previously, so this is probably a fairly common user-case.

I've had this same error appear for at least the past 5 years whenever installing a new release of Ubuntu, but since the process of establishing repeatable conditions for an installation problem that occurs at the _end_ of an installation is very time-consuming, it's only now that I've got around
to making sure that non-formatting the partition during the installation _is_ the issue. It is. The problem goes away if the partition is formatted during the installation.

There are pages of Google hits for the string "An error occurred while restoring previously-installed applications". Users that read the error message are understandably concerned, and ask how they find out which applications need to be "manually installed" as per the message.

Here's two forum posts where the posters did eventually realize that formatting the partition during the installation made the problem go away:

For Kubuntu 15.10: https://askubuntu.com/questions/698727
For Ubuntu 16.04: https://ubuntuforums.org/showthread.php?t=2394271

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.