grass-qgis-postgis next to each other on ubuntu 14.04

Dear all,

I am not sure whether this is the right channel to ask for, but I can
not install grass7, qgis and postgis-2.2 next to each other on my
Kubuntu 14.04 machine. I posted this question already to the grass
mailing list, but I think it links this list as well.

I use ubuntu-gis unstable and this (deb
http://apt.postgresql.org/pub/repos/apt/ trusty-pgdg main) repo.

I can either install postgis or grass and qgis, so I think the issues
must be somehow between conflicting files between both repositories.

12:48 $ sudo apt-get install grass-core
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
grass-core : Depends: libgdal20 (>= 2.0.1) but it is not going to be
installed
Depends: libgeos-c1v5 (>= 3.4.2) but it is not going to be
installed
Depends: liblas-c3 (>= 1.8.0) but it is not going to be
installed
Recommends: gdal-bin but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

When I go an start to install the dependencies, my machine either
complains about other missing dependencies or for the case of
'libgeos_clv5' wants to remove postgis.

14:14 $ sudo apt-get install libgeos-c1v5
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
libgeos-3.5.0 libspatialite5
The following packages will be REMOVED
libgdal1h libgeos-c1 liblwgeom-2.2-5 postgis postgis-gui
postgresql-9.5-postgis-2.2
The following NEW packages will be installed
libgeos-3.5.0 libgeos-c1v5
The following packages will be upgraded:
libspatialite5
1 to upgrade, 2 to newly install, 6 to remove and 0 not to upgrade.
Need to get 1,376 kB of archives.

Any help is appreciated.

Cheers,

Stefan

--
Stefan Lüdtke

Section 5.4- Hydrology
Phone: +49(0)331-288-2821
Fax: +49(0)331-288-1570
Email: sluedtke(at)gfz-potsdam(dot)de
___________________________________________

Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
Foundation under public law of the federal state
of Brandenburg
Telegrafenberg, D-14473 Potsdam