MOLD and NVidia and Drivers...oh god...

novafacing · September 5, 2022

Linux   Debian

I’m half making a note to self. I recently reinstalled Debian on my desktop (I had switched from Ubuntu 20.04 to Debian Sid on my laptop earlier this summer), but my laptop does not have a discrete GPU. My desktop does! All actually went well the first time I installed.

$ aptitude search '~i !~M' -F '%p' | sed "s/ *$//" | sort -u | grep nvidia
nvidia-detect
nvidia-driver
nvidia-kernel-common
nvidia-kernel-dkms
nvidia-support
nvidia-xconfig

So it seems I ran:

$ sudo apt-get -y install \
	nvidia-detect \
	nvidia-driver \
	nvidia-kernel-common \
	nvidia-kernel-dkms \
	nvidia-support \
	nvidia-xconfig \

And everything worked well, even picom using gl backend! This was fine and dandy for a week, when I installed mold.

MOLD Linker

If you haven’t been paying attention, you may not know that there is a new linker in town that promises to be:

  • A drop-in replacement for (lld/ld.bfd/ld.gold)
  • MUCH faster than all three of those

I was having issues compiling and quickly linking large rust packages, so I decided to give mold a try. It’s packaged for Debian already, so installing is as simple as:

$ sudo apt-get install mold

I also wanted to use mold as my default linker, so I also did:

$ sudo update-alternatives --install /usr/bin/ld ld $(which mold) 100

If you haven’t used update-alternatives before, it’s basically a much smarter way to symlink programs into your $PATH so that:

  • You can list what you’ve symlinked
  • You can change symlinks around
  • You don’t have to actually run ln -s ever
  • Your system won’t break as easily

And it worked awesome! As I tweeted, mold didn’t crash when ld.bfd did, and compiled some rust code about 10 times faster! Awesome!

NVidia is broken! :(

This morning, happy with my linker and my graphics drivers, I noticed I had quite a lot of updates to install and did the ususal:

$ sudo apt-get update && sudo apt-get upgrade && sudo reboot now

(You don’t have to reboot after updates, but it turns out that when GL gets updated both VSCode and Kitty Terminal go bonkers).

When I logged back in I was greeted by a very ugly low resolution login. Obviously a driver issue. I logged in, reinstalled nvidia-driver and nvidia-kernel-dkms, and rebooted again. No dice. I purged all my nvidia packages and reinstalled them:

$ sudo apt-get purge '*nvidia*'
$ sudo apt-get install -y \
	nvidia-detect \
	nvidia-driver \
	nvidia-kernel-common \
	nvidia-kernel-dkms \
	nvidia-support \
	nvidia-xconfig \

Still no dice. This is when I started getting bad vibes and looked back through the apt logs. Turns out that the reason for the failure is that nvidia-kernel-dkms failed to build the NVidia kernel module required to run the GPU. Fair enough, but I didn’t know why…except that there’s really only one reason. I had a (correct) hunch that mold can’t handle the NVidia kernel module compilation process yet, so I reset the alternative:

sudo update-alternatives --install /usr/bin/ld ld /usr/bin/ld.bfd 101

And it worked! So I guess I won’t be using mold as a symlink anymore! Instead, I recommend just adding:


LD=/usr/bin/mold

To your shell’s .rc file.

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