Update
The changed suggested by Jeroen van Bussel on Oct '15 worked
https://community.openhab.org/t/problem-getting-exec-binding-to-execute-command/2872/35
Namely
1> /etc/default/openhab - change to root (USER_AND_GROUP=root:root)
2> /usr/lib/systemd/system/openhab.service
- change user and group inside the file
User=root
Group=root
sudo service openhab restart
Regards
Steve