[DESKTOP] Kubuntu 18.04 not detecting multiple monitors, cannot extend - ATI Radeon HD 5750

[Spectrum]

Hi! On a fresh installation of Kubuntu 18.04 on a desktop computer I have this problem: I have two monitors attached. In "System Settings -> Display and Monitor" I cannot see my two monitors. My display is just duplicated across the two, and I have no option to extend it across them.

It might have to do with my graphics card. My card is an ATI Radeon HD 5750.

I had to boot the installer with the flag nomodeset just to get it to start (as described in this thread). Now I do not explicitly set any nomodeset parameter when booting Kubuntu, but maybe it has set some system setting; I don't know.

I tried looking for drivers. The AMD website does not have a driver for my specific card for (K)ubuntu 18.04. It does have one for Ubuntu 14.04, but that DEB cannot run because it cannot satisfy dependencies. There is also a generic "Linux" driver on the AMD website, but I want to ask before I try to install that.

Does anyone know what I need to do in order to get my monitors recognized?

Thanks in advance!

[Bings]

It's because you have to boot in nomodeset, you can't set dual monitors properly. I have the exact same issue with my 7870, it's annoying as crap.

[jlittle]

When I used to do nomodeset, it was a temporary measure to get the OS running so that I could install a video driver (it was nvidia onboard graphics). Once the driver was in, the OS could boot in a sensible mode.

[claydoh]

Setting nomodeset on the installer does not enable it on the installed system - you'd have to have manually edited some config files for grub for that to happen, so this is likely not the issue.

There is no longer a proprietary driver for this card. The open source driver is the only choice.
In the Monitor section of System Settings, try dragging the monitor image around - it is moveable. The two screens may just be on on top of the other. This would make the two mirrored, which is what you are seeing. You can position them how you like. Touching side to side, or top to bottom creates an extended desktop, having them separated makes them different desktops.

[Spectrum]

It's because you have to boot in nomodeset, you can't set dual monitors properly. I have the exact same issue with my 7870, it's annoying as crap.

Setting nomodeset on the installer does not enable it on the installed system - you'd have to have manually edited some config files for grub for that to happen, so this is likely not the issue.

It turns out that Bings is right: The installer did set nomodeset as a default boot option. I can see it when I press "e" in grub.
And the bad news is, I cannot boot without it. If I remove it in grub, the problem from my other thread returns: The monitors lose signal as soon as I leave grub.

A snippet of my boot options look like this:

There is no longer a proprietary driver for this card. The open source driver is the only choice.

Can I somehow check whether that is properly installed?

In the Monitor section of System Settings, try dragging the monitor image around - it is moveable. The two screens may just be on on top of the other. This would make the two mirrored, which is what you are seeing. You can position them how you like. Touching side to side, or top to bottom creates an extended desktop, having them separated makes them different desktops.

Thanks, but I've tried dragging it around. There is definitely only one.

[Bings]

IIRC something called Universal Mode Setting was removed and replaced with Kernel Mode Setting. I believe it the lack of this UMS that is the cause of the problem of the post grub black screen and there is no way to get dual monitors working properly on either of our graphic cards. That said, I think I got it working on a live version of Fedora using Wayland but it was very buggy and I don't think I get results on an install. So you might want to experiment with Wayland stuff, I don't know how advanced it is nowadays.