[ubuntu-uk] Screen resolution problems on dual-monitor setup

Jim Price d1version at hotmail.com
Wed Aug 10 11:53:21 UTC 2011

On 10/08/11 12:00, James Morrissey wrote:
> Hi all,
> I posted this on the forums yesterday, but haven't had much luck. I
> was wondering if anyone here could help.
> I am trying to set up dual monitors in Ubuntu, with the two monitors
> having different resolutions. One monitor is on my laptop and the
> other is an external monitor. I have an ATI Radeon express 200m doing
> the graphics.

That probably means you have to use the ATI open source driver IIRC.

> For the two monitors i would like to have one showing at
> 1280x800 and the other at 1280x1024. At the moment the resolution has
> defaulted to 1024x768.

Do you know if the spec of your Radeon 200m supports these resolutions 
combined? I would guess it does, but I'm not sure without googling it. 
Do you know if it uses its own memory or shares system memory, and if 
so, how much?

> I have seen a number of threads detailing this problem, but none seem
> to solve my issue. Here is a run down of how far i have gotten on
> different fronts.
> 1. Talks about editing xorg.conf.
> - The problem here is that i don't seem to have an xorg.conf file in
> /usr/share/X11. When I "locate xorg.conf" in the terminal i get:
> /usr/share/X11/xorg.conf.d
> /usr/share/X11/xorg.conf.d/10-evdev.conf
> /usr/share/X11/xorg.conf.d/11-evdev-quirks.conf
> /usr/share/X11/xorg.conf.d/50-synaptics.conf
> /usr/share/X11/xorg.conf.d/50-vmmouse.conf
> /usr/share/X11/xorg.conf.d/50-wacom.conf
> /usr/share/X11/xorg.conf.d/51-synaptics-quirks.conf
> /usr/share/doc/xserver-xorg-video-nouveau/examples/xorg.conf
> /usr/share/man/man5/xorg.conf.5.gz
> As such i am not sure which file to try and edit.

Leave those alone for now.

> 2. Try changing resolution on one of the monitors in
> ~/.config/monitors.xml, which is where i got the unity dock to only
> show on the primary monitor.
> - Here, after i saved the changes to ~/.config/monitors.xml, and
> logged out, i got an error message saying  that the resolution would
> not work as i logged in.

What was the exact error message you got?
Can you post the monitors.conf you have at the moment?

> Both monitors then came up as they were
> initially. When i looked at ~/.config/monitors.xml, i saw that the
> resolutions had reverted back to what they were originally.
> 3. Talks about editing xrandr, linking to this page
> http://www.ubuntugeek.com/how-change...ng-xrandr.html
> - This looks incredibly intimidating and i can't really work out what
> to do in my case. Any advice would be much appreciated.

xrandr isn't as complicated as the documentation makes it look. If you 
want more advice on this option you will need to state which version of 
Ubuntu you are using though, as it has changed a bit over the last few 

> 4. I think is a GUI method for the solution offered by 3 (above). This
> involves trying to 'configure display settings' in 'monitor
> preferences'. Here i can change the resolution of each monitor quite
> easily. This works and the resolution is perfect. The problem though
> is once i have set the resolution to what i want for both monitors,
> they begin to behave strangely. Most notable is that when i close
> things they don't disappear off the screen (although they appear to
> have closed), the unity dock smears on the screen when it minimizes
> and mouse pointer labels show up and then don't disappear.

I think you would need to create an xorg.conf to use this method, as it 
would need the total X screen area defined in order to work.

> So i am now stumped. If anyone can tell me either how to sort the
> resolution, interpret the xrandr instructions or fix the screen
> smearing i would be very grateful.

I'm up for having a go at bouncing a few ideas around. I think your 
option 4 is probably the one to start with, although I think it will 
involve a certain amount of overlap with option one. I've used xrandr, 
and it might be useful, but option 4 would be needed too as xrandr will 
not help you have two monitors showing different parts of the same 
desktop (which is what you will have to do if you want different 
resolutions on each screen - if you want cloned screens, you need the 
same resolution on each).

First I need to know what version of Ubuntu you are running, as there 
are differences between them, and I like to post stuff which I can test 
in the same environment before I post it. Then we can start constructing 
a suitable xorg.conf. You also need to decide which of the two windows 
is going to have the (I assume) Gnome menus on it.


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