Why did CSM make boot fail after 3+ years of no problems?
 

Hello!
I have an Asus H170 motherboard that has been running Linux Mint 18 (based on Ubuntu 16.04) for 3+ years no problem with no BIOS changes. CSM has been enabled, despite booting in EFI mode.

I did not do any major software changes and simply used applied the recommended updates. Yesterday, it could not boot and went straight to a black screen.

I was unable to troubleshoot and since I had all my data backed up and wanted to try a newer version, I wiped the drive and installed Linux Mint 19.1 (based on Ubuntu 18.04).

I then had the SAME problem! I then went into the BIOS and tried every setting. I discovered that CSM was the culprit. As soon as I disabled it, it was fine and the PC is running great.

But why? After so many years, why did CSM make my boot fail? And is there a bigger underlying problem? I cannot disable Secure Boot in the BIOS. Not sure if there is a driver or something causing secure boot to fail and try to switch over to legacy boot, but if so, why does disabling CSM help?

I am trying to understand where exactly it was failing so I can better understand it. Any insight would be appreciated! Thank you!

Bumping this to see if anyone can offer any insight? I'm curious if a kernel change made it impossible to boot with CSM mode enabled?

What is "CSM"? Some of us may not know the acronym; I certainly do not. Also, have you checked the log files for any hints?

As an aside, LQ frowns on "bumping" one's own post. Zero-reply threads automatically get a "bump," and bumping the post with a reply takes it off the zero-reply list and may reduce its visibility, as many LQ regulars start with the zero-reply list.

Compatibility Support Module. Some info at the link below or do an online search with the parameters "uefi and csm". Basically allows Legacy boot on a UEFI machine and varies a lot with manufacturers.

https://en.wikipedia.org/wiki/Unifie...ware_Interface

That's a manufacturer setting or should be. Were you ever able to do this on the Asus.

I'm not sure why disabling the CSM option allowed booting your UEFI install but since you have only UEFI it isn't necessary. Did you reboot immediately after each change you made in the BIOS settings to test?

Thanks for the reply!

I never did try to disable secure boot on the Asus. I did reboot immediately after every BIOS setting to test, and discovered CSM was the culprit. I believe it was always set to be enabled, so not sure what changed to make my last previous install fail.