So far the best way to get it working without breaking a possible background running installation ( as it could happen by removing the lock file), is stopping the service using apt:
Error:
# sudo apt-get upgrade
E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?`
Solution:
sudo systemctl stop apt-daily.timer
