command-not-found crashing with incomplete locale settings

command-not-found should have printed some more information as seen in the following:

            print >> sys.stderr, _("command-not-found version: %s") % version
            print >> sys.stderr, _("Python version: %d.%d.%d %s %d") % sys.version_info
            try:
                import subprocess
                subprocess.call(["lsb_release", "-i", "-d", "-r", "-c"], stdout=sys.stderr)
            except (ImportError, OSError):
                pass
            print >> sys.stderr, _("Exception information:")
            print >> sys.stderr
            print >> sys.stderr, ex
            try:
                import traceback
                traceback.print_exc()
            except ImportError:
                pass

Regardless I don't think command-not-found tell people goto to +filebug but rather launch ubuntu-bug for you or just let apport catch the crash. I'll open a separate bug for that.

How did you perform the fresh install with your old home? I'm curious if this is a problem other people might encounter.

/home is a separate partition so all I did was that I wiped my root filesystem "/".

Right, but how did you install? Did you use the Live CD of Ubuntu 12.04 and choose to upgrade an old release of Ubuntu to 12.04 or perform a fresh install leaving your home directory alone?

Sorry. Didn't understand your question.
I used LiveCD. I marked the partition with my old / to format and mount as '/' (so the old system was really completely wiped out byt the mkfs). In the same dialog I marked my home partition to mount as /home and _do not_ format.

Actually.. I used the i386 liveCD of 11.10, installed 11.10 (but didn't install any 11.10 update from the internet) and only then upgraded to 12.04.

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

You can also replicate this on a very-bare install that has no language packs at all.

I can confirm this bug as well, I observed it on three different systems running Ubuntu 12.04. I installed each of these systems using the alternative Installer, selecting English as the System Language, German Keyboard and en_US.UTF8 for the locale (which seems to be a fix to the bug I reported here back in 2008 already: https://bugs.launchpad.net/ubuntu/+source/debian-installer/+bug/229699).

Update: Actually I can confirm that on systems where the "setting locale failed" problem appears also command-not-found is broken and crashes as reported by Martin here. When you get rid of the "setting locale failed" problem, command-not-found does not crash anymore.

But nevertheless, even if the locale cannot be set correctly command-not-found should not crash but give a hint to the problem like i.e. "perl" does:

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = "en_US:en",
        LC_ALL = (unset),
        LC_PAPER = "a4",
        LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

I also got into this state, installing 12.04.1 from the desktop CD, selecting en_US language, german keyboard, german number and date format (de_DE).

Got this problem too, Ubuntu 12.04.1 with command-not-found 0.2.44

I found that if the chosen locale was not generated first (locale-gen), then it will cause this problem.