The last time I ran multiheaded Linux, I was on Kubuntu 12. Since that time I’ve built about a half dozen machines with same or similar hardware: a couple dual-dvi Nvidia cards. They mostly ran Windows, but it’s 2016 and time to kick Windows out again.
Upon initial install, three of the monitors are basically functional and Kde display settings detect the fourth, but won’t let me enable it. A little research and I remember that I used to use Xinerama.
In 2012, Nvidia supported multi-head configurations on Linux with its proprietary X extension, Xinerama. It was a bit quirky, but worked well enough so long as you had a set configuration you didn’t want to change often.
So I install the binary blob Nvidia drivers, enable Xinerama and get only black screen plus a cursor shaped like the letter x.
It seems that Nvidia abandoned Xinerama and they now say to use something called Base Mosaic. After reading many instructions and questions about this setup and tweaking xorg.conf every way I can imagine, I conclude that Base Mosaic can only span multiple video cards when they are connected via sli, and even if I had cards with that capability, it’s not clear whether I could expect it to work for more than three monitors.
Essentially, I have the wrong hardware. So I abandon the hostile Nvidia and instead order two Radeon cards.
Ati used to ship binary driver blobs, but also made specs available that enabled development of more reliable open source drivers. In the last few years, Ubuntu dropped support for the binary blob “fglrx” drivers, reasoning that the open source drivers are adequate, so the the fglrx packages no longer appear in official repositories for Kubuntu 16.
Two Radeon cards go in and all four monitors come to life. It looks like progress. Unfortunately, though active, they are barely usable: my mouse suffers terrible jerkiness and screens briefly freeze from time to time. I spend the rest of the day trying different combinations of Linux and window managers: i3 on Ubuntu, Kde on Centos, Gnome 3 on Centos, Cinnamon on Mint. All suffer similar problems and the fglrx drivers from ElRepo just crash.
I observe that the the problems go away so long as I use only one card at a time. So, I reason that I still don’t have the right hardware. I order a quad-head card, the VisionTek Radeon 5570. Finally, five video cards, later, I start Kubuntu and everything just works.
Short story: for multi-head Linux in 2016, use a single video card and avoid Nvidia.
Should Be Simple 