How to upgrade a server from 12.04 to 16.04?
Solution 1:
General
You can always upgrade from LTS to LTS, in your case that would mean:
- upgrade from 12.04 to 14.04 and then
- upgrade from 14.04 to 16.04
As far as i know there is no supported upgrade from 12.04 to 16.04 directly.
Following this approach there is no need for your 16.04 medium
As always, consider creating a backup of your critical files before you start.
Limit to LTS
The way to limit upgrades to LTS without a GUI is to change the value of Prompt in /etc/update-manager/release-upgrades.
Set it to
[DEFAULT] Prompt=lts
The possible values are
never: Never check for a new release.
normal: Check to see if a new release is available. If more than one new release is found, the release upgrader will attempt to upgrade to the release that immediately succeeds the currently-running release.
lts: Check to see if a new LTS release is available. The upgrader will attempt to upgrade to the first LTS release available after the currently-running one. Note that this option should not be used if the currently-running release is not itself an LTS release, since in that case the upgrader won't be able to determine if a newer release is available
How to upgrade
For both upgrade processes you should always update the current system via
sudo apt-get update
sudo apt-get upgrade
Then start the upgrade via
sudo do-release-upgrade
or - SPECIAL CASE - for development versions (which is valid for upgrades from 14.04 to 16.04 until 16.04.1 was released):
sudo do-release-upgrade -d
If do-release-upgrade command is not found, install it:
sudo apt-get install update-manager-core