openssh-server package not available on 12.04.2

Open the terminal and type:

sudo apt-get install openssh-server

If that doesn't work, open the Ubuntu Software Center and browse to Edit -> Software Sources -> Ubuntu Software tab, and make sure that you have at least the main, universe and multiverse repositories marked with a check mark.

Go to the Ubuntu Software Centre and browse to the Edit -> Software Sources -> Ubuntu Software tab. Then select Other -> Select Best Server under Download From.

Afterwards run in a terminal (Ctrl+Alt+T):

sudo apt-get update && sudo apt-get install openssh-server

Follow the on-screen instructions. This will resolve the issue.

I was following the advice to remove and re-install openssh-server via CLI, but got an error saying the package was not available.

Update apt-get then tried again with success.

So, the sequence that succeeded was:

sudo apt-get remove openssh-client openssh-server
sudo apt-get update
sudo apt-get install openssh-server