Fixing Linux display issues

 So recently I made what I thought was a small upgrade to my computer - I added a second SSD to my desktop. Fairly simple, power off, remove the power cord, open the case find a spot, an open SATA port, and a power connector to the SATA SSD, and voila. 

Problem was it booted in low graphics mode. That was odd. Run an update, reboot, and now doesn't want to boot at all. 

What I now know - or think - happened was a dead CMOS battery like this one. Since the board is quite old at this point, the battery had gone away, meaning that upon shutting down and pulling the power all the BIOS settings etc were gone. That means the system goes to the default.

This isn't a problem for the most part, but did warrant a new coin cell battery. Because I was getting boot issues the quick fix was to remove the graphics card and use onboard graphics. However, the graphics card was the most expensive part of the system, and I wanted to get it working. After replacing the coin cell battery and using the computer for a few days without the card, I found some time and willpower to open it up again and poke around. 

Steps: 

• Card goes in, DVI-D connect (old computer) goes to the card
• Does it boot? 'Yes' skip the next step, 'No' do this next step
• A couple of things to try if there isn't a post screen - 
• If there is no post (the initial Vendor logo that should say something like "Press F2 or DEL to enter setup"), power off unplug. Popping out the coin battery will reset BIOS settings if that was a culprit/factor. 
• Re-seat memory which in my case was just to reverse the placement of my 2 DIMMs.
• If you get boot and can get to Linux start screen try to log in. 
• I was using an NVIDIA card on Ubuntu 20.04 Gnome for this and the NVIDIA settings weren't coming up. (NVIDIA X server)
  
• Open the terminal and run lspci <- make sure you see the card listed
• You can also run lspci | grep NVIDIA to shorten the list, if you have an NVIDIA card
  
• At here either the driver is missing corrupted or, and I think more likely, the display manager got out of whack.
• Background: Linux like any other OS has a kernel component that interacts and can talk with the graphics drivers. If the setting gets messed up for any reason, it needs to be reset.
• For good measure I reinstalled the Nvidia graphics driver which in Ubuntu if you already setup the proprietary driver is (last number is the version so please ensure you are installing the version you want)
  sudo apt reinstall nvidia-driver-460
  
• In my case running dpkg-reconfigure lightdm then selecting gdm3 as the display manager and reboot fixed the issue. 
• Do check what the display manager is best suited for the distro / desktop variant you are using. This computer was first installed with Ubuntu 16.04 (2016.04 - April 2016), and updated all the way to today. Meaning, it has both Unity and Gnome desktops which caused a few issues when I accidentally set lightdm as the default rather than gdm3 <-- cool thing about Linux is it still worked! Though it wasn't ideal, it worked relatively well aside from a couple of hot-keys. To verify whether to use lightdm or gdm3 view here. 
• Alternatively you can run sudo service lightdm status or sudo service gdm3 status to check if either is running to find the default.
  

 

 

I hope that is helpful. Since I came across the issue I figured I'd share it.