ubuntu 20.04 upgrade to 21.04 code example
Example 1: upgrade ubuntu 16.04 to 20.04
sudo apt update && sudo apt upgrade
sudo do-release-upgrade
Example 2: update to 21.04 from 20.04
$ sudo apt update
$ sudo apt upgrade
$ sudo apt dist-upgrade
sudo apt update && sudo apt upgrade
sudo do-release-upgrade
$ sudo apt update
$ sudo apt upgrade
$ sudo apt dist-upgrade