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Official documentation can be found at https://help.ubuntu.com/.

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Use the Official Ubuntu Documentation page to find the official installation guide for the version and platform you desire to install. For example, the installation guide for 18.04 of amd64 is here.

Ubuntu Server

Server documentation: https://ubuntu.com/server/docs

Netplan documentation: https://netplan.io/

Kubuntu

Installation

See Kubuntu Help and Support. Download and use the PDF for the desired version.

Package Management

Disabling auto update

APT::Periodic::Update-Package-Lists "0";
APT::Periodic::Unattended-Upgrade "0";

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It also may be necessary to do:

# apt remove unattended-upgrades

Switching version of major packages

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Upgrading Ubuntu

First, fully upgrade your existing installation:

# apt update
# apt upgrade

# apt remove ros-*
# apt autoremove
# rm /etc/apt/sources.list.d/ros-latest.list
# apt update

Finally, remove unneeded stuff, reboot to make sure the system still boots, then do the release upgrade:

# apt autoremove
# reboot
# apt do-release-upgrade

Troubleshooting

If something happens and you lose the terminal, try the steps at https://serverfault.com/a/427008.

ssh <machine you're upgrading>
# screen -list
# screen -d -r root/2953.ubuntu-release-upgrade-screen-window