Ubuntu Server distribution upgrade

Doing a distribution upgrade is easy in the graphical user interface.  On a "headless" Ubuntu Server, you probably don't have a graphical user interface available, and you need to perform a few easy steps.

First you need to check 2 things:

• The package "update-manager-core" needs to be installed.  Just run the following command: (it will install it, if it is not already)

  sudo apt-get install update-manager-core

• On Ubuntu Server, the update channel is usually "LTS" (Long Time Support) which will upgrade only to the major release of Ubuntu Server.  Probably, you want to set this to "normal", to allow an upgrade to every distribution upgrade.  To do this open the file "/etc/update-manager/release-upgrades", and change the line "Prompt=lts" to "Prompt=normal".
  For example, with pico:
  

  sudo pico /etc/update-manager/release-upgrades
  
  Change the Prompt setting to "normal".
  
  Press Ctrl-X, press "Y" to confirm and press enter to confirm the filename.

Then the distribution upgrade can be started by running this command:

sudo do-release-upgrade -d 

It is not "recommended" to do a distribution upgrade remotely over ssh.  The "do-release-upgrade" command above checks on this, and gives a warning.  However, I didn't have any problem doing the upgrade remotely over ssh.