Updating ubuntu from command line
On Digital Ocean systems, it is safe to ignore this warning and proceed with the upgrade, since a local mirror for 16.04 is in fact available. Continue [y N] Details [d] New packages will now be retrieved, then unpacked and installed.
My system is already up to date (I updated yesterday).
On a system you have modified heavily, you may wish to enter d and inspect the list of packages to be removed, in case it includes anything you'll need to reinstall later.
You may need to press a key here to exit to your local prompt, since your SSH session will have terminated on the server end.
Some major, very- and incompatibly-different versions get packages.
For instance, Python 2.6, Python 2.7, Python 3.1 all live in separate packages on Ubuntu.