I tested the upgrade from bionic to cosmic using the oibaf graphics drivers PPA and with the version of the release upgrader from -proposed received the following message:
"An unresolvable problem occurred while calculating the upgrade.
This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.
If none of this applies, then please report this bug using the
command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal.If
you want to investigate this yourself the log files in
'/var/log/dist-upgrade' will contain details about the upgrade.
Specifically, look at 'main.log' and 'apt.log'."
I tested the upgrade from bionic to cosmic using the oibaf graphics drivers PPA and with the version of the release upgrader from -proposed received the following message:
"An unresolvable problem occurred while calculating the upgrade.
This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.
If none of this applies, then please report this bug using the release- upgrader- core' in a terminal.If dist-upgrade' will contain details about the upgrade.
command 'ubuntu-bug ubuntu-
you want to investigate this yourself the log files in
'/var/log/
Specifically, look at 'main.log' and 'apt.log'."
Setting to verification done.