I want to downgrade from Ubuntu 18.04 back to Ubuntu 16.04. The installer does not recognize that I currently have Ubuntu 18.04 installed, and I don't want to lose my data. Any help is greatly appreciated.

enter image description here

Here I select "Something else"

![2]: https://i.stack.imgur.com/SuART.png

When sda selected, it does not detect root. Note: my disk is encrypted

![3]: https://i.stack.imgur.com/kmnQR.png


You can install 16.04 (or any other Ubuntu version) over your current installation. It won't interfere with your personal data. As long as you don't specify format the partition, it'll just delete system directories that your specified version uses.

It'll also inform you of this with this message:

The file system on /dev/sdXY assigned to / has not been marked for formatting. Directories containing system files (/etc,/lib,/usr,/var,...) that already exist under any defined mountpoint will be deleted during the install.

Those directories will not have your data in them. Your home folder will not be touched. Also some local system areas such as /usr/local/... and /opt will not be touched.

There's a chance that some of the configuration files in your /home directory might cause some errors when you log in. You'll have to manually fix those. I usually do it by creating a new user when performing this type of install. Then I login between the two users, while I fix the applications or configurations that causes errors.

  • Thanks L.D. Should I select "Do something else" and then a specific sda to follow your instructions or do I choose the install option which warns me I will lose all data on the disk? Please see the image link I added to the main post. – Beh May 10 '18 at 2:07
  • Your image is showing that you have selected erase the entire disk. You will lose everything if you choose that option. You would have to click the bottom option that says Something Else. That is the option that allows you to choose where to install Ubuntu. That is the option that will only delete the system folders as long as you don't checkmark Format the partition. – L. D. James May 10 '18 at 3:33
  • When selected Something Else and leaving Format the partition unchecked, I receive a warning that no root file system is selected. What do I do from here? Please note my disk is encrypted, if that makes a difference in this situation. – Beh May 10 '18 at 12:08
  • The encryption doesn't make any difference. You have to how you will be using the partition. Click on the Change partition near the bottom of the window and specify /. That is telling the installer your selection for the root partition`. – L. D. James May 10 '18 at 13:39

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