How to upgrade Linux Mint 20.3 to 21 without GUI?

Question

I found out I cannot update multiple packages any more. That was disappointing considering I chose the LTS version to avoid this issue.

The system in question is one that I only seldom use, and when I do I use remote desktop or SSH terminal. The problem is the recommended way to upgrade to Linux Mint 21 is to use a GUI tool called mintupgrade:

sudo apt install mintupgrade
sudo mintupgrade

This will throw an error when connected via remote desktop, presumably because it needs a real hardware screen:

No protocol specified
Unable to init server: Could not connect: Connection refused
No protocol specified
Unable to init server: Could not connect: Connection refused
No protocol specified
Unable to init server: Could not connect: Connection refused

(mintupgrade.py:4622): Gtk-WARNING **: 00:12:10.928: cannot open display: :10.0

Running it in an SSH session produces a similar error:

(mintupgrade.py:5106): Gtk-WARNING **: 00:20:59.670: cannot open display:

So, is there a way to do this via the command line, or do I have to move some monitor or a TV to the computer just to do the upgrade?

Answer 1

I had exactly the same problem when I performed several consecutive upgrades from Mint 19.1 to 20.3 and then I got stuck on this step. And after some searching I found the solution that worked for me here.

Basically, the superuser doesn't have a configuration to access local X server, so the most simple solution is to copy this configuration from existing local user via sudo cp ~$USER/.Xauthority /root.

Please note that if you are running this command from a user which doesn't have a configured GUI entry (in my case, it was running from admin, which have elevated privileges, but without interactive login, while I was logged in interactively under another, restricted user) you need to substitute $USER variable with the name of the user which have this configuration.