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Comment by rufugee | Hacker News Reader

I'm one of those weird folk who run three monitors, and even though 12.04 promised better 2+ monitor support through Unity 2D, I still find it lacking. Perhaps it's the way I have it configured, but I use two nvidia cards with xinerama, which means I'm forced to use Unity 2D (no compositing support). Unity 2D just isn't as stable or usable. I really, really hope they put more effort to fixing this in 12.10.

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I fought with this in the past. In the end I unhappily switched to back to windows running linux VMs after years of using linux as my primary desktop OS, and it was purely because of this failure.

Don't expect multiple graphics cards to work well under linux, at all. I tried this for quite awhile and there are a number of bugs. The one that bit me the most was that when a mouse cursor cross a screen boundary that switches GPUs and there is an animated cursor running, the mouse gets all messed up with the clicks being sent to the wrong screen, click on screen 1 and the event is sent to screen 2. I also had constant issues across many version of X with the Xorg process pegging a CPU core and making the system unusable.

Xinerama is all but deprecated it seems, RandR was supposed to replace the multiple graphics card support and allow multi-gpu composting but the project hasn't gotten around to it despite the fact that they've been talking about multi-gpu handling for more than 3 years.

My "workaround" for a long time was using a Matrox tripleHead2Go to let me get 4 monitors onto a single nvidia card. But, this approach has inherent limitations, all displays have to be oriented the same way and have to be side by side, what I wanted was one screen in landscape, 2 in portrait on the sides and a couple extra above.

At this point the best bet is hoping that wayland handles multi-gpus far better than X does.

Have you tried Nvidia TwinView? This should let you operate the monitors with some 3D support.

TwinView works for two monitors on one graphics card, but once you get a second card you'll need xinerama, ergo no 3d support.

An ATI card that supports 3 monitors (needs to have a displayport connector and you need an "active" displayport adapter or a monitor with a displayport connector) should work. But don't tell anyone I recommended an ATI card for linux.

What ard0r said about TwinView. I'm anxiously awaiting TripletView from Nvidia...

ard0r, if you were to recommend an ATI card which had three display ports, what would it be? And, as a guy who has used nvidia with Linux for the past, oh, 14 years or so, can you tell me why you seem reluctant to recommend an ATI (AMD)? Am I inviting trouble by purchasing one?

The proprietary drivers have worked OK for me, but I've had issues with playing video. I just couldn't get smooth framerates. The radeon driver was worse in that aspect. I swapped in two nvidia cards and video looked much better. It should be fine for general use and I'm still trying to make the ATI setup work. I don't need 3D, just video.

I have a 5870 eyefinity 6 that has 6 display ports, but those are no longer made and expensive (and overkill).

I found a $60 Radeon HD 6450 card made by Sapphire on Newegg (N82E16814102960) that has two dvi and one displayport, that should work for three monitors. There are other options as well of course, just make sure the cards are advertised as supporting eyefinity and they have at least one displayport adapter. I've had success with an Accel active displayport to DVI adapters.

Thanks....I may try an AMD. I don't need 3D support either, but I do need compositing support (does no 3D mean no compositing? Not sure...).

Not having compositing on the linux desktop these days means you're a second class season. Both Unity and Gnome3 require it to function...if you don't have it, you have to fall back to Unity2D (incomplete user experience) or Gnome 2 (no longer supported. KDE actually does the best of the bunch when it comes to Xinerama so far, but I really prefer Unity or Gnome3.

I've read that if you buy two similar Nvidia cards (same GPUs), you can get compositing across three monitors, but I've not spoken with anyone who can verify. If anyone reading this can, please provide your vid card model.

Do you know if this Radeon HD 6450 will support compositing across three monitors? $60 is cheap to me to get this.

Thanks!

It looks like that specific card won't work for three monitors, because output #3 is hdmi and not displayport.

I'm currently using a NVIDIA GT218 (for one monitor) and a GT520 (for two other monitors) on my Arch Linux system. Although Xinerama support is nearly unusable with this setup (most likely due to the different chipsets on the cards), you can do TwinView (for two monitors) and a separate X screen (for the third) or 3 separate xscreens. I just do 3 separate xscreens (I'm a gamer and don't like to see my quake client stretched across two of my monitors and my TV :) ). You can't move windows between monitors with Xinerama or TwinView, but that's a sacrifice I was willing to make for my configuration. I am able to do compositing across all three of my monitors with this configuration.

Anyway, I hope this helps!

That's useful to know.

Actually, the N82E16814102960 is dual-link DVI + DVI + HDMI.

TwinView also doesn't support rotating one of the screens, which is a show stoppper for me.

Actually, it "does", but it requires some magical incantations, and you end up with a virtual desktop with lots of off-screen pixels, and your desktop/window manager has problems figuring that out. That's why I started using the Nouveau drivers; it fully supports Xrandr, which means you can use the desktop manager's built-in screen rotation abilities.

Thanks for that. I've been meaning to retry the Nouveau drivers... ISTR there was some other thing that they didn't support which is why I don't use them. Guess I'll have to try to re-enable them again to learn what that is.

Ah yes... think I remember now... they didn't like connecting one of my monitors with DisplayPort. Or didn't seem to.

I've recently ordered 3x 21.5" monitors for developing with. It'll be interesting to see how Precise / Unity handles that setup. I have either Nvidia Optimus on my T420s Thinkpad or ATI 5970s to test with.

I've got that setup with a 5970 eyefinity 6 card. The monitors are in portrait mode so it's like one big 3240x1920 surface.

Developing what with? I got hacked off with issues with multiple monitors - and in the end - just went back to one monitor with multiple work spaces. I figured in the end they were nothing but a distraction.

So do you normally go back to 1 monitor or Windows?

did you try Gnome-shell ? I dont have multi monitors myself, but I have read reports that it is better.

I use gnome-shell instead of Unity on Ubuntu, and have multiple monitors. I use focus follows mouse not click to focus, so unity's whole app menu thing is ridiculous. I actually measured that I'd have to move the mouse over a metre on screen for my common window layout to get to menus. Sure I could fight all this, but I'd rather use something that is standard across distros and not Ubuntu proprietary.

That said, gnome-shell doesn't work correctly with multiple monitors. In particular workspaces affect the first monitor but not the second one so they are annoying to use. Sometimes programs going full screen on the second monitor can't be restored. There are no context menu items to move items amongst workspaces. Since the available space on each screen differs (resolution, various bars) windows can end up with the wrong size.

None of these issues existed with Gnome 2. Gnome 3 was basically 5 steps forward and 10 steps back. I do like some of those forward steps. Unfortunately the cost turns out to be loss of functionality and humungous CPU/memory consumption (I upgraded my 8GB machine to 16GB because of it!)

FWIW I spent 6 months running Gnome 3.0 on a laptop with a core 2 duo, intel graphics, and 4GB of RAM without noticing any performance problems.

That is the exact same spec as my laptop. I don't actually notice performance problems from gnome shell because I spend most of my time typing with short bursts of compilation etc. But when running top, gnome shell is always up there and has accumulated a huge amount of CPU time. More than X and the web browsers put together usually. Memory consumption varies so where I notice problems is when things have been swapped out because of gnome shell memory usage. I've never had it around 10gb but Alan Cox has https://plus.google.com/111104121194250082892/posts/5f5XXtRG...

Have you tried Gnome? I also use 2 monitors, and hope that Gnome on 12.04 supports multi-monitors well.

I use Unity with 2 monitors and it is pretty good; but I didn't try Gnome

I run with Unity in one window and Windows xp in vmware in another 24" without problems. Gnome works too.

All you need to ensure is you have decent video card/drivers

I'm using 3 monitors in 12.04 under Unity without a hitch! Then again, I'm using 1 ATI video card (with 3 outputs) and the proprietary ATI driver.

Unity has great support for multiple-monitors. Many, if not most, of the problems are due to: X, the video card drivers and Xinerama.

Huh. Then I'll give it a try.

I always disabled Unity until now, precisely for the reason that it didn't work for me on this laptop that is often docked with 2 monitors.

Yep...in case anyone comes back to this thread, I purchase an AMD Sapphire Radeon FLEX HD 6770 1GB DDR5 PCIe 2.1, and Unity works perfectly across all three now using the proprietary drivers, and setting the "Multi-display desktop" option for each monitor in the amdcccle utility.

I haven't tried it with 12.04 yet, but I've had poor experience getting Gnome installed and running decently in the last couple versions of Ubuntu. It seems like Fedora is the easiest way to use it.

I've been using Gnome3 (on Fedora) with 2 monitors for a while now, and it works perfectly.

I have. Gnome 3 refuses to load with three monitors on Xinerama...but I have heard it works ok with two...just as Unity does. It's when you go to three that things get rough.

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