How to Upgrade Ubuntu 16.04 to 18.04 LTS Server
sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
reboot
sudo apt install update-manager-core
sudo vim /etc/update-manager/release-upgrades
set prompt=lts
sudo do-release-upgrade -d
reboot
lsb_release -a
sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
reboot
sudo apt install update-manager-core
sudo vim /etc/update-manager/release-upgrades
set prompt=lts
sudo do-release-upgrade -d
reboot
lsb_release -a