A. Introduction

This tutorial explains how to upgrade to LMDE 3.

B. General considerations

B1. Did you create a system snapshot?

If anything breaks or if anything goes wrong during the upgrade, you can go back in time and revert all changes by restoring your latest system snapshot. Whatever happens, you're covered.

B2. Did you make backups?

Your personal data is the most valuable thing in your computer. If anything happens and you break your operating system, it's not a problem, it can be reinstalled or restored via a system snapshot. If you lose your data or you're unable to access it... that's a different story.

To be safe, make a full backup of your data on an external device (USB stick or DVD).

C. Requirements

To upgrade to LMDE 3 you need to satisfy the following requirements.

C1. Experience with APT and the command line

Upgrading to a newer package base is not trivial and it should not be performed by novice users.

You need to know how to type commands and read their output.

You also need to be experienced with APT.  During the upgrade you'll need to understand the output of APT commands. You'll need to understand if a package needs to be removed, if it blocks the upgrade, if it conflicts with another package etc etc.

C2. LMDE 2 Cinnamon edition

The upgrade tool only upgrades LMDE 2 Cinnamon edition.

The MATE edition of LMDE was discontinued.

C2. Timeshift snapshot

To install timeshift, open a terminal and type:

apt install timeshift

Then launch "Menu -> Administration -> Timeshift".

Follow the wizard to select a destination for your snapshots.

In the toolbar, click on the "Create" button to make a manual snapshot of your operating system.

If anything goes wrong, you'll be able to restore your operating to this current state, either from within LMDE, or by launching Timeshift from a live Mint session (live DVD or live USB).

C2. LightDM

To know which display manager you are currently using, open a terminal and type:

cat /etc/X11/default-display-manager

If the result is "/usr/sbin/lightdm", you can skip this step.

If the result is "/usr/sbin/mdm", you need to switch display managers by installing lightdm and removing mdm. Open a terminal and type:

apt install lightdm lightdm-settings slick-greeter

When asked to choose a display manager between MDM and LightDM, choose LightDM.

Open a terminal and type:

apt remove --purge mdm mint-mdm-themes*

sudo dpkg-reconfigure lightdm

sudo reboot

D. How to upgrade

D1. Update your LMDE 2 system

Using the Update Manager, click on "Refresh" to refresh the APT cache and apply all updates.

D2. Give your terminal unlimited scrolling

Open a terminal.

Click on "Edit"->"Profile Preferences"->"Scrolling".

Check the "unlimited" option and click "OK".

D3. Install the upgrade tool

To install the upgrade tool, open a terminal and type:

apt install mintupgrade

D4. Check the upgrade

To simulate an upgrade, open a terminal and type:

mintupgrade check

Then follow the instructions on the screen.

This command temporarily points your system to the LMDE 3 repositories and calculates the impact of an upgrade.

Note that this command doesn't affect your system. After the simulation is finished, your original repositories are restored.

The output shows you if the upgrade is possible, and if it is, which packages would be upgraded, installed, removed and kept back.

It is extremely important that you pay close attention to the output of this command.

Keep using "mintupgrade check" and do not proceed to the next step, until you're happy with the output.

D5. Download the package upgrades

To download the packages necessary to upgrade to LMDE 3, type the following command:

mintupgrade download

Note that this command doesn't actually perform the upgrade itself, but just downloads the packages.

Note also that this command points your system to the LMDE 3 repositories (if you want to go back to LMDE 2 after using this command, you still can, with the command "mintupgrade restore-sources").

Use the "mintupgrade download" command until all the packages are successfully downloaded.

D6. Apply the upgrades

Note: This step is non-reversible. Once you perform it, the only way to go back is by restoring a system snapshot. Make sure you've made a snapshot before following this last step.

To apply the upgrades, type the following command:

mintupgrade upgrade

D7. Downgrade foreign packages

Some packages either no longer exist in LMDE 3, or have a lower version than in LMDE 2 (MATE packages in particular were version 1.18 in LMDE 2 but only 1.16 in LMDE 3 now that MATE is no longer maintained by LMDE but maintained by Debian directly). To guarantee they function properly, they need to be downgraded.

Launch the Software Sources tool from "Menu -> Administration -> Software Sources".

Open the "Maintenance" tab and click on "Downgrade Foreign Packages".

Select all foreign packages and click "Downgrade".

D8. Delete foreign packages

Launch the Software Sources tool from "Menu -> Administration -> Software Sources".

Open the "Maintenance" tab and click on "Remove Foreign Packages".

Select all foreign packages and click "Remove".

E. Alternatives

If you cannot upgrade please perform a fresh installation.

Generic instructions on "fresh upgrades" are also available at https://community.linuxmint.com/tutorial/view/2

F. Notes

• It is recommended to use the default Linux Mint mirror before upgrading, to make sure you're using the latest version of mintupgrade. You can check your version of mintupgrade with "apt policy mintupgrade".
• The upgrade overwrites files in /etc/ with default configuration files. You can restore files indivually by the Timeshift snapshot you made prior to upgrading.
• A known issue affects Timeshift. When restoring a snapshot, if the "Disclaimer" window is empty, wait for about 2 minutes for the text to appear. Once the disclaimer text is there you can press Next and restore your snapshot. Pressing Next before the text appears results in a failure to restore. If you did, reboot and try to restore again.
• If for some reason you do not want to use timeshift, you can force the upgrader to not require it by typing the following command: "sudo touch /etc/timeshift.json".