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As mentioned in the title, I boot my PC and select the Ubuntu OS that I have and then it gets stuck on an infinite loading screen.

I tried setting appending nomodeset to the grub but that didn't help me. Any suggestions?

After hitting escape on the loading screen to get prompted with some information about the system operations I found the following:

[  OK  ] Starting User Runtime Directory /run/user/...
[FAILED] Failed to start Light Display Manager
See 'systemctl status lightdm.service' for details
[  OK  ] Finished User Runtime Directory /run/user/... .
         Starting User Manager for UID 10000...
[  OK  ] Started User Manager for UID 10000...
[  OK  ] Stopped Light Display Manager. 
         Starting Light Display Manager.
         Starting RealtimeKit Scheduling Policy Service.
[  OK  ] Started RealtimeKit Scheduling Policy Service.
[FAILED] Failed to start Light Display Manager.
         Starting Light Display Manager...
[FAILED] Failed to start Light Display Manager.
See 'systemctl status lightdm.service' for more details.

And then it continues with the aforementioned failed start Lightdm messages. At the end of the prompts, I see

A start job is running for Hold until the boot process finishes up ( <mins> / no limit)

where <mins> is the time until the infinite loading process began I presume

Plus I try to get prompted a terminal via (alt + ctrl + f1/f2) to view the file but I cannot get any kind of terminal. It simply takes me back to the loading screen and then back to the messages.

But if I reboot the machine and then select advanced options for ubuntu from the OS select menu I can get a root shell prompt. But I do not have internet access since I tried running a sudo upgrade and the fetches failed.

So how do I fix the issue without networking ?

ex1led
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1 Answers1

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So what the main problem was that the display manager was not working correctly. The most common solutions/suggestions that you can find on this topic (e.g., [1],[2]) do recommend (among others) that you dpkg reconfigure the lightdm package. But in order to do so, you need some terminal prompt.

As mentioned above I was not able to access any kind of terminal by using ctrl + alt + f1/f2. What I did actually, was to access ubuntu in recovery mode and from there get a root terminal in order to proceed with the reconfiguration of the lightdm package.

After I logged in as a #root I did sudo dpkg-reconfigure lightdm and then rebooted my machine. The error persisted and so I tried to remove completely and then re-install the display manager. I followed the same steps, selected Ubuntu Recovery mode from the OS select menu, and then I selected enable networking before I open a root terminal in order to have a network connection and be able to fetch the package.

Seems that I've opened Pandora's box at this point. There is a bug ( see [3],[4] ) in the recovery mode, and although I am using UbuntuMATE 20.04 and the error concerns an older version of the kernel apparently it still exists (?). So...I had first to enable the Networking of my system manually.

I removed (sudo rm) the dangling link of /etc/resolv.conf -> /run/resolvconf/resolv.conf and then I created another resolv.conf file at /etc/ dir with valid DNS servers. I saved the file and restarted the network manager. After that I tried ping 8.8.8.8 and I got a response.

# resolv.conf file 
nameserver 8.8.8.8 # primary   DNS server for Google DNS
nameserver 8.8.4.4 # secondary DNS server for Google DNS

Since I now had access to the internet I did the following:

  1. sudo apt purge xorg lightdm
  2. sudo apt autoremove
  3. sudo apt install xorg lightdm

After rebooting the machine I was able to log-in successfully.

ex1led
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