Enabling remote desktop mode is extremely easy on Ubuntu since Dapper.
Now that you’ve been warned of the risks, let’s move on.
Navigate to the System \ Preferences \ Remote Desktop on the Gnome top menu.
The second checkbox should always be checked, and you should enter a secure password.
You will be prompted for this password when you have a go at log on.
Tested on: Ubuntu Dapper Drake, Ubuntu Edgy Eft
