@xuanruiqi I recently upgraded from 17.10 to 18.04. Steam was prompting for a few packages at first, but it was due to the fact that I upgraded with a mesa PPA that could not transition to 18.04. This left my system in an unstable state, and I have now fixed my issue. What I should have done was used something like ppapurge before upgrading.

Are you using a PPA or somehow have conflicting versions of mesa packages?

I fixed my issue by manually removing the old 17.10 PPA from files located in /etc/apt/sources.list.d/. If you have access to "Software & Updates" you could just remove them from there as well. Then running the following dpkg command to manually remove these packages without removing any packages that depend on them (sounds like what you're trying to do). Again, I verified these packages were all left over from the PPA via the version strings. Perhaps you could run the command just with the packages that are giving you issues:

sudo dpkg -P --force-all xserver-xorg-video-radeon xserver-xorg-video-intel-dbg xserver-xorg-video-intel xserver-xorg-video-ati xserver-xorg-video-amdgpu mesa-vulkan-drivers mesa-vdpau-drivers mesa-va-drivers mesa-va-drivers:i386 libxatracker2 libwayland-egl1-mesa:i386 libwayland-egl1-mesa libosmesa6:i386 libosmesa6 libglapi-mesa:i386 libglapi-mesa libgl1-mesa-glx:i386 libgl1-mesa-glx libgl1-mesa-dri:i386 libgl1-mesa-dri libgbm1:i386 libgbm1 libegl1-mesa:i386 libegl1-mesa libllvm7:i386 libllvm7

Once I removed all the packages from that PPA, I ran:

sudo apt-get update

Which reported all the unmet dependencies. To fix that I had to run:

sudo apt --fix-broken install

I also ended up running the following because CSGO would run, but was crazy slow:

sudo apt-get install --reinstall xserver-xorg-video-intel xserver-xorg-core
sudo dpkg-reconfigure xserver-xorg

May require reboot as well.

Not sure if this will help you, but it corrected my mismatched package versions and got Steam and CSGO functioning again.

Hm, I use the graphics-drivers/ppa PPA, but no mesa PPAs. The former doesn't contain mesa, I think. Looks weird to me.

I didn't update my system from 16.04 but rather installed a fresh version of 18.04. So conflicting PPAs shouldn't be a problem.

On my system (also Ubuntu 18.04 LTS), I was able to fix this by manually installing libgl1-mesa-glx:i386 using aptitude instead of apt. Aptitude will suggest options for fixing the conflict, and if you say no then it will try a different option. For me, the first suggestion was to uninstall a bunch of stuff; after I said no, the second suggestion was do nothing (don't install anything), and the third option was to downgrade libgl1-mesa-glx [18.0.5-0ubuntu0~18.04.1 (now) -> 18.0.0~rc5-1ubuntu1 (bionic)], which seems to do the trick for me.

I'm closing this, because I'm no longer using Ubuntu anymore, as of Dec 2018, so no longer a problem for me :smile: Hopefully this thread will be useful to some Ubuntu users though.

This issue ~is currently~ was preventing steam from starting on my Ubuntu 18.04 system.

$ apt install -y libgl1-mesa-dri:i386 libgl1-mesa-glx:i386
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
 libgl1-mesa-dri:i386 : Depends: libllvm7:i386 (>= 1:7~svn298832-1~) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

If I try to install libllvm7 directly, I get this:

$ apt install -y libllvm7:i386
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
 gvfs : Depends: gvfs-daemons (>= 1.36.1-0ubuntu1.2)
        Depends: gvfs-daemons (< 1.36.1-0ubuntu1.2.1~)
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.

This is weird because I don't have any held packages. apt-mark showhold reports nothing.

I found someone else reporting this a couple of months ago to Ubuntu, but they seemed to reject that it was a bug on their side: https://bugs.launchpad.net/ubuntu/+source/mesa/+bug/1803849

I tried to use synaptic to install libllvm7:i386 manually, and to resolve the issue it tried to uninstall my desktop environment, among other things.

What finally fixed it was to run the purge command suggested by @nightsky30 above: sudo dpkg -P --force-all xserver-xorg-video-radeon xserver-xorg-video-intel-dbg xserver-xorg-video-intel xserver-xorg-video-ati xserver-xorg-video-amdgpu mesa-vulkan-drivers mesa-vdpau-drivers mesa-va-drivers mesa-va-drivers:i386 libxatracker2 libwayland-egl1-mesa:i386 libwayland-egl1-mesa libosmesa6:i386 libosmesa6 libglapi-mesa:i386 libglapi-mesa libgl1-mesa-glx:i386 libgl1-mesa-glx libgl1-mesa-dri:i386 libgl1-mesa-dri libgbm1:i386 libgbm1 libegl1-mesa:i386 libegl1-mesa libllvm7:i386 libllvm7

I kept an eye on what was removed, then tried to reinstall things. I suspect the issue may have been caused by a custom LLVM repository I was using, which I disabled before reinstalling things. Now it all works, so thanks @nightsky30 !

@pwaller You are very welcome. I'm glad that helped :)

@pwaller thank you for posting this because it fixed my issue. I also had custom llvm repo on mine.

See also https://github.com/ValveSoftware/steam-for-linux/issues/2800#issuecomment-661855621 which gives specific guidance for working out if multiarch libllvm packages match, which is what had to be fixed to resolve this symptom for me (and also has some useful background on why this is a recurring problem).