do-release-upgrade fails when using update-alternatives to provide different versions of /usr/bin/python

[Daniel Ricao Canelhas]

sudo do-release-upgrade

fails to upgrade 13.04 to 13.10 when update-alternatives is used to maintain different versions of python

e.g.
sudo update-alternatives --list python
/usr/bin/python2.7
/usr/bin/python3.3

The script complains that the symlink to /usr/bin/python is broken regardless of which version is being used to provide python

a workaround is to remove the symbolic link

`sudo rm /usr/bin/python`

and creating it manually

`sudo rm /usr/bin/python`
`sudo ln -s /usr/bin/python2.7 /usr/bin/python`
`sudo do-release-upgrade`

Apparently using version 3.3 didn't work too well either.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: ubuntu-release-upgrader-core 1:0.205
ProcVersionSignature: Ubuntu 3.11.0-12.19-generic 3.11.3
Uname: Linux 3.11.0-12-generic x86_64
ApportVersion: 2.12.5-0ubuntu2
Architecture: amd64
CrashDB: ubuntu
Date: Fri Oct 18 11:42:03 2013
MarkForUpload: True
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: release-upgrade
UpgradeStatus: Upgraded to saucy on 2013-10-18 (0 days ago)

[Daniel Ricao Canelhas (daniel-canelhas)]

Found a log with the actual error

[Daniel Ricao Canelhas (daniel-canelhas)]

I'm guessing the solution in general should be to check if the symbolic link points to a file or to a symbolic link and keep following the links until a file is reached (unless the symlinks point around in a circle somehow)

ls /etc/alternatives
...
lrwxrwxrwx 1 root root 62 Jul 5 22:25 policytool.1.gz -> /usr/lib/jvm/java-7-openjdk-amd64/jre/man/man1/policytool.1.gz
lrwxrwxrwx 1 root root 18 Oct 18 11:39 python -> /usr/bin/python2.7
lrwxrwxrwx 1 root root 12 Jul 5 17:02 rcp -> /usr/bin/scp
...

[Daniel Ricao Canelhas (daniel-canelhas)]

so, in /DistUpgrade/DistUpgradeController.py

after line 381, inserting something like this would possibly patch this bug:

                while os.path.islink(fs_default_version) :
                    fs_default_version = os.readlink(fs_default_version)

It would be an endless loop if links are circular though. Adding a counter for a maximum depth is one way out...
Another would be to add the visited links to a list and checking it to see if the current link is already in the list. If so. break and return an error of some sort. But it would be a very unusual configuration to find.

[Launchpad Janitor (janitor)]

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