sudo add-apt-repository -y ppa:ubuntugis/ubuntugis-unstable
sudo apt update
sudo apt upgrade # if you already have gdal 1.11 installed
sudo apt install gdal-bin python-gdal python3-gdal
sudo vim /etc/apt/sources.list
deb https://qgis.org/ubuntugis bionic main
deb-src https://qgis.org/ubuntugis bionic main
sudo apt-get update & sudo apt-get upgrade
sudo apt-get install -y qgis python-qgis qgis-plugin-grass grass-gui