Q:

Cannot run Grass algorithms in QGIS 2.18 on Ubuntu 16.04

I have QGIS and GRASS installed through the UbuntuGIS repositories. If I try to execute any GRASS 6 or 7 algorithm I get the following error message:
"This algorithm cannot be run :-( It seems that GRASS GIS 7 is not correctly installed and configured in your system. Please install it before running GRASS GIS 7 algorithms."
I checked other questions on this issue however most deal with Setup on Windows systems:

"Missing dependency.This algorithm cannot be run :-(" QGIS + GRASS Windows 7
Grass 6 extension installation in Grass 7 error
How to make GRASS 7 addon available in QGIS 2.12?

On linux I do not have to configure the path of the GRASS folder as the QGIS help on configuring external applications tells me. Grass runs from the shell by typing grass. The Grass-version called by the shell is GRASS 7.2.0 (2016). 
Furthermore i checked that GRASS 6 and 7 is activated in the additional providers menu in the toolbox of QGIS.
Any suggestion what could be done to fix this?
Edit
Meanwhile I completly uninstalled and reinstalled qgis python-qgis qgis-plugin-grass from the oficial QGIS repositories...but the error continues. 
Edit 2
Checking out the logs for qgis in the Log Messages Panel I found out under the "plugins" tab that the grass plugin does not load properly:
2017-01-23T14:10:22 1   Failed to load /usr/lib/qgis/plugins/libgrassplugin7.so (Reason: Cannot load library /usr/lib/qgis/plugins/libgrassplugin7.so: (libgrass_gis.7.0.3.so: cannot open shared object file: No such file or directory))
2017-01-23T14:10:22 1   Failed to load /usr/lib/qgis/plugins/libgrassprovider7.so (Reason: Cannot load library /usr/lib/qgis/plugins/libgrassprovider7.so: (libgrass_gis.7.0.3.so: cannot open shared object file: No such file or directory))
2017-01-23T14:10:22 1   Failed to load /usr/lib/qgis/plugins/libgrassrasterprovider7.so (Reason: Cannot load library /usr/lib/qgis/plugins/libgrassrasterprovider7.so: (libgrass_gis.7.0.3.so: cannot open shared object file: No such file or directory))

A:

I get the same error with the Ubuntugis version of QGIS and GRASS version 7.2.0.
It seems that 7.2 is not yet correctly adopted in processing. There is already a ticket for it: https://hub.qgis.org/issues/16019 and https://lists.osgeo.org/pipermail/qgis-developer/2017-January/046671.html
As a workaround, you may edit (as sudo) /usr/share/qgis/python/plugins/processing/algs/grass7/Grass7Utils.py line 251 to 
            command = 'grass72 ' + Grass7Utils.grassMapsetFolder() \

and line 103 of Grass7AlgorithmProvider.py to
    return 'grass72'

Or downgrade to GRASS 7.0.3 from the main Ubuntu repo.
GRASS 6 commands will not work with GRASS 7, so you can deactivate the 161 GRASS commands.

Just another workaround from the mailing list https://lists.osgeo.org/pipermail/qgis-user/2017-January/038907.html
sudo ln -s /usr/bin/grass72 /usr/bin/grass70

UPDATE
Also reported with http://hub.qgis.org/issues/16110 and fixed with http://hub.qgis.org/projects/quantum-gis/repository/revisions/099e7a77f2c32f469539f542a31df7b0d4b77dd3 That should work for GRASS versions 7.0 up to 7.3
Unfortunately, the fix has not been applied to QGIS 2.18.4, so the workarounds are still necessary.

A:

I fixed the problem by reinstalling grass 7.0.3 from the qgis repository.
The grass from Ubuntugis repo is version 7.2, which is not support by QGIS.

remove the GRASS GIS by
sudo apt-get remove grass grass-core grass-doc grass-gui
disable ubuntugis-unstable repository
sudo apt-get install grass grass-gui

It works for me.

