Release upgrade fails with error about PPAs -- but no PPAs installed

[Greg Ward]

I ran update-manager to upgrade to Ubuntu 23.10. It downloaded a bunch of stuff and churned for a while, and then popped up this error dialog:

> Could not calculate the upgrade
>
> 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 do have several third-party repos configured in /etc/apt/sources.list.d, but not of them are PPAs. Here's what I have:

```
$ cat brave-browser-release.list
deb [signed-by=/usr/share/keyrings/brave-browser-archive-keyring.gpg arch=amd64] https://brave-browser-apt-release.s3.brave.com/ stable main

$ cat google-cloud-sdk.list
deb [signed-by=/usr/share/keyrings/cloud.google.gpg] https://packages.cloud.google.com/apt cloud-sdk main

$ cat ngrok.list
# deb https://ngrok-agent.s3.amazonaws.com buster main # disabled on upgrade to mantic

$ cat slack.list
### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
# deb https://packagecloud.io/slacktechnologies/slack/debian/ jessie main # disabled on upgrade to mantic

$ cat vscode.list
### THIS FILE IS AUTOMATICALLY CONFIGURED ###
# You may comment out this entry, but any other modifications may be lost.
# deb [arch=amd64,arm64,armhf] http://packages.microsoft.com/repos/code stable main # disabled on upgrade to mantic
```

The bottom of /var/log/dist-upgrade/main.log says this:

```
2023-11-10 18:38:31,862 DEBUG Marking 'ubuntu-desktop' for upgrade
2023-11-10 18:38:32,045 WARNING Can't mark 'ubuntu-desktop' for upgrade (E:Unable to correct problems, you have held broken packages.)
2023-11-10 18:38:32,045 DEBUG Marking 'xubuntu-desktop' for upgrade
2023-11-10 18:38:32,210 WARNING Can't mark 'xubuntu-desktop' for upgrade (E:Unable to correct problems, you have held broken packages.)
```

Hmmmmmmmmm.

ProblemType: Bug
DistroRelease: Ubuntu 23.04
Package: ubuntu-release-upgrader-core 1:23.04.7
ProcVersionSignature: Ubuntu 6.2.0-1007.7-lowlatency 6.2.12
Uname: Linux 6.2.0-1007-lowlatency x86_64
ApportVersion: 2.26.1-0ubuntu2.1
Architecture: amd64
CasperMD5CheckResult: pass
CrashDB: ubuntu
CrashReports:
 600:117:124:37:2023-11-10 12:50:34.011233923 -0500:2023-11-10 09:50:34.782762954 -0500:/var/crash/_usr_libexec_xfce4-screensaver-dialog.1000.uploaded
 644:1000:124:0:2023-11-10 09:50:34.189762709 -0500:2023-11-10 09:50:34.189762709 -0500:/var/crash/_usr_libexec_xfce4-screensaver-dialog.1000.upload
 640:1000:124:3001891:2023-11-10 09:50:34.188762708 -0500:2023-11-10 09:50:34.223762723 -0500:/var/crash/_usr_libexec_xfce4-screensaver-dialog.1000.crash
CurrentDesktop: XFCE
Date: Fri Nov 10 18:40:52 2023
InstallationDate: Installed on 2022-11-28 (347 days ago)
InstallationMedia: Ubuntu 22.10 "Kinetic Kudu" - Release amd64 (20221020)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to lunar on 2023-11-10 (0 days ago)
VarLogDistupgradeTermlog:

[Greg Ward (gward)]

Trying to repair the broken packages did nothing:

```
$ sudo apt-get -f install
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

$ sudo apt-get -f install ubuntu-desktop
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
ubuntu-desktop is already the newest version (1.501).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

$ sudo apt-get -f install xubuntu-desktop
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
xubuntu-desktop is already the newest version (2.248).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
```

[Greg Ward (gward)]

I also tried

```
sudo apt remove ubuntu-desktop xubuntu-desktop && sudo apt install ubuntu-desktop xubuntu-desktop
```

which resulted in no net change. Here's what the `install` command did:

```
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following NEW packages will be installed:
  ubuntu-desktop xubuntu-desktop
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 5,116 B of archives.
After this operation, 22.5 kB of additional disk space will be used.
Get:1 http://archive.ubuntu.mirror.rafal.ca/ubuntu lunar/main amd64 ubuntu-desktop amd64 1.501 [2,570 B]
Get:2 http://archive.ubuntu.mirror.rafal.ca/ubuntu lunar/universe amd64 xubuntu-desktop amd64 2.248 [2,546 B]
Fetched 5,116 B in 1s (9,663 B/s)
Selecting previously unselected package ubuntu-desktop.
(Reading database ... 469204 files and directories currently installed.)
Preparing to unpack .../ubuntu-desktop_1.501_amd64.deb ...
Unpacking ubuntu-desktop (1.501) ...
Selecting previously unselected package xubuntu-desktop.
Preparing to unpack .../xubuntu-desktop_2.248_amd64.deb ...
Unpacking xubuntu-desktop (2.248) ...
Setting up ubuntu-desktop (1.501) ...
Setting up xubuntu-desktop (2.248) ...
```

[Greg Ward (gward)]

Finally, I commented out all of /etc/apt/sources.list.d/*.list and re-ran update-manager. It still failed, but this time the error message was a bit different. There's nothing about PPAs.

> Could not calculate the upgrade
>
> An unresolvable problem occurred while calculating the upgrade.
>
> 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'.

[Greg Ward (gward)]

This problem has magically disappeared! I gave up on it for the weekend and shut the laptop down. Came back to it Monday morning, and the upgrade to 23.10 worked just fine.

I have no idea if any of my actions fixed it. There were definitely no updates applied between giving up Friday evening and trying again Monday morning. I just tried again, and it worked that time.

[Launchpad Janitor (janitor)]

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