Upgrade from 15.10 to 16.04: Could not calculate the upgrade

[Flaburgan]

The system asked me for an upgrade, I accepted.

I first had this information message:
```
Third party sources disabled

Some third party entries in your sources.list were disabled. You can re-enable them after the upgrade with the 'software-properties' tool or your package manager.
```

I validated the popup and the upgrade started but then I had this message:

```
Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

 This can be caused by:
 * Upgrading to a pre-release version of Ubuntu
 * Running the current pre-release version of Ubuntu
 * Unofficial software packages not provided by Ubuntu

If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal.
```

I never used a pre-release of Ubuntu and I'm not upgrading to a pre-release. I don't know how to check what "unofficial package" I have and which could cause that. My /etc/apt/sources.list looks clean:

```
# deb cdrom:[Ubuntu 15.04 _Vivid Vervet_ - Release amd64 (20150422)]/ vivid main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://fr.archive.ubuntu.com/ubuntu/ wily main restricted
deb-src http://fr.archive.ubuntu.com/ubuntu/ wily main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://fr.archive.ubuntu.com/ubuntu/ wily-updates main restricted
deb-src http://fr.archive.ubuntu.com/ubuntu/ wily-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://fr.archive.ubuntu.com/ubuntu/ wily universe
deb-src http://fr.archive.ubuntu.com/ubuntu/ wily universe
deb http://fr.archive.ubuntu.com/ubuntu/ wily-updates universe
deb-src http://fr.archive.ubuntu.com/ubuntu/ wily-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://fr.archive.ubuntu.com/ubuntu/ wily multiverse
deb-src http://fr.archive.ubuntu.com/ubuntu/ wily multiverse
deb http://fr.archive.ubuntu.com/ubuntu/ wily-updates multiverse
deb-src http://fr.archive.ubuntu.com/ubuntu/ wily-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://fr.archive.ubuntu.com/ubuntu/ wily-backports main restricted universe multiverse
deb-src http://fr.archive.ubuntu.com/ubuntu/ wily-backports main restricted universe multiverse

deb http://security.ubuntu.com/ubuntu wily-security main restricted
deb-src http://security.ubuntu.com/ubuntu wily-security main restricted
deb http://security.ubuntu.com/ubuntu wily-security universe
deb-src http://security.ubuntu.com/ubuntu wily-security universe
deb http://security.ubuntu.com/ubuntu wily-security multiverse
deb-src http://security.ubuntu.com/ubuntu wily-security multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu wily partner
# deb-src http://archive.canonical.com/ubuntu vivid partner
```

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: ubuntu-release-upgrader-core 1:15.10.14.4
ProcVersionSignature: Ubuntu 4.2.0-38.45-generic 4.2.8-ckt10
Uname: Linux 4.2.0-38-generic x86_64
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Mon Jun 20 14:40:13 2016
InstallationDate: Installed on 2015-10-05 (258 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to wily on 2016-06-20 (0 days ago)
VarLogDistupgradeTermlog:

[Flaburgan (flaburgan)]

Description of the bug updated to provide error messages. Please tell me which log to check to know what caused the `Could not calculate the upgrade` message.

[Flaburgan (flaburgan)]

Here is the PPA I have activated. Does anyone know which one is causing trouble?

ls -l /etc/apt/sources.list.d/
total 20
-rw-r--r-- 1 root root 130 jun 21 10:02 atareao-ubuntu-atareao-wily.list
-rw-r--r-- 1 root root 130 jun 21 09:59 atareao-ubuntu-atareao-wily.list.distUpgrade
-rw-r--r-- 1 root root 111 jun 21 10:02 pgdg.list
-rw-r--r-- 1 root root 111 jun 21 09:59 pgdg.list.distUpgrade
-rw-r--r-- 1 root root 111 avr 8 11:34 pgdg.list.save
-rw-r--r-- 1 root root 0 jan 14 11:37 stk-ubuntu-dev-wily.list
-rw-r--r-- 1 root root 0 jan 14 11:37 stk-ubuntu-dev-wily.list.save

[Flaburgan (flaburgan)]

After a look at `/var/log/dist-upgrade/main.log` it looks like postgis was in fault.

sudo apt-get remove postgresql-9.2-postgis-2.1
sudo apt-get remove postgresql-9.4-postgis-2.1

Allow the upgrade to launch (it will install postgresql-9.5-postgis-2.2)

[Flaburgan (flaburgan)]

The upgrade went fine, I had to reinstall postgresql-contrib after that though.

sudo apt-get install postgresql-contrib-9.2
sudo apt-get install postgresql-contrib-9.4

Then I was able to drop and recreate postgis extension in psql.

This issue can be closed, sorry for the noise. I'd like to suggest to add the name of the blocking package to the error modal though, it would have saved me a lot of time.

[Launchpad Janitor (janitor)]

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