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Re: Pining for Qt 5.4

On 05/02/2015 04:00 PM, Markus-Hermann Koch wrote:
> thanks for your detailed answer!
> Sigh. I am still hoping to avoid experimental on this one (being
> already traumatized from past experiences culminating in complete
> reinstallation into my now clean 'unstable' system with its single
> media package libdvdcss2).

Well, if you do pin experimental packages to -1 by default, APT will
never install them, even if you ask it to.

For example, if I want to install libkf5config-dev (only in
experimental so far), have experimental in my sources.list.d but also
pinned to -1, using APT has the following result:

# apt-get install libkf5config-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package libkf5config-dev is not available, but is referred to by another
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'libkf5config-dev' has no installation candidate

This means that no packages from experimental can be installed by
default, you have to explicitly pin them again to make certain packages

On my own box, I did exactly the steps I wrote in my previous mail to
test the installation of Qt 5.4 (I'm running Jessie, Qt5 previously not
installed at all), and running apt-get install qt5-default it installed
Qt5 packages from experimental, but all other packages from Jessie.

This works now because Qt 5.4 doesn't have any dependencies on stuff
that's only in experimental, so you will currently get ONLY Qt 5.4, but
everything else will be from other suits.

Now, if at some point you want to install something from experimental
that does have additional deps on other experimental packages, you will
have the following stuff happen:

 - first you just pin the packages you want themselves to 500
 - then you try to install them with APT. that will tell you that it
   can't resolve dependencies (and it will also tell you which ones)
 - then you take a look at the dependencies you'd need from experimental
   and see if you think you can live with that - if so, just add them
   to the list of packages pinned to 500 (if you pin by releaese, you
   can add the deps to the same list as the original package, if you pin
   by version, you need to create a new block with the new version

My guess is that in your previous attempt you added experimental to your
sources.list but didn't pin the release to a negative number, so other
packages might have automatically crept in in some cases, screwing up
your system that way. But if you pin experimental to a negative number,
you have to explicitly pin those packages that you want back to a
positive number in order for APT to consider them as candidates for your

> Still: If I can make your priority based updating work and if it
> does not require pulling too important other testing/experimental
> libraries into my system I will give it a shot.

As I said: currently Qt 5.4 is installable without any deps on stuff
that's not already in unstable.

If you understand what pinning does (and what different priority ranges
mean), then you can use that to selectively install packages from
different suits / different repositories without having the risk that
other packages from those repositories 'contaminate' your system. You
only have to keep in mind that 'apt-cache policy' is your friend if APT
complains about stuff, because with that you can check what's going on.


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