problems with 10.04 upgrade to 12.04

Avi Greenbury lists at
Thu Sep 6 17:39:29 UTC 2012

Dave Howorth wrote:

> I've already said that I don't understand apt and dpkg much but I'm
> confused by why apt and dpkg show different things:
>  # apt-cache search 'python.*minimal'

Here you're asking apt for available packages
>  # dpkg -l \* | grep minimal

Amd here you're asking dpkg for a list of installed packages.

> Why does dpkg not know about the new versions?

Essentially, dpkg is the package manager. It is responsible for
installing and uninstalling packages, and keeping track of which
version of what you have installed. It is only concerned with what's
going on locally.

apt* (the apt- tools and aptitude) are the remote bits - they know
where packages come from and can go and get them. When you ask one of
them to install a package they first check with dpkg that it isn't
already installed, and then check with their own cache to find whether
it is available. If it is available they then download it and ask dpkg
what else needs to be installed for the package to work. They then go
and repeat the process for each of these packages (and all and any of
their dependencies). Once they've downloaded the list of packages they
then get dpkg to install them.

> And what decides what should be installed?
> i.e. why does apt-get say:
>   python-minimal: Depends: python2.7-minimal (>= 2.7.3) but it is not
> going to be installed

The maintainer of the python-minimal package has said, when building
the package, that it requires python2.7-minimal of version 2.7.3 or

There's a few reasons it might be 'not going to be installed
unfortunately, and apt is rarely clear on the reasons. You can try
attempting explicitly installing it:

  apt-get install python2.7-minimal

to see if that is more wordy on reason. It's *possible* (but I'd hope
unlikely) that 2.6 conflicts with 2.7.


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