Dual Monitor: How to Get Full Resolution

[Kent Borg]

Gleeful Report:

This is for Ubuntu 8.04, Jaunty Jackalope.

I have a notebook with an external VGA output jack.  When I plugged it
into an external LCD that is 1440x900, it wouldn't give me full
dimensions for that monitor.  Oddly, I have another install of 8.04 on a
USB stick and it all works fine there.

After some Googling and poking around, I fixed it!

I think the key was that the dimensions mentioned in /etc/X11/xorg.conf
were too small in both directions.  I boosted the vertical to 900 and
the Display control panel was suddenly willing to mention the 1440x900
choice, and when I chose that it offered to change the virtual
resolution...and when I checked it had changed the horizontal.

I logged off and on again, and it would let me go to 1440x900 on that
other screen!


Summary:

If you have a multi-display setup and can't get full resolution on one
of your displays, check /etc/X11/xorg.conf.  (It is a small file these
days.)  Make sure the virtual display dimension is big enough for all
your displays.


Example:

I have two displays 1024x768 and 1440x900.  I told the Display control
panel (System->Preferences->Display) that the two displays are
side-by-side.  This means I need a virtual display that is 2464 wide and
900 tall to fix them both in.

In the file /etc/X11/xorg.conf I had this:

  Section "Screen"
      Identifier    "Default Screen"
      Monitor        "Configured Monitor"
      Device        "Configured Video Device"
      SubSection "Display"
          Virtual    2304 768
      EndSubSection
  EndSection

Note the line that says "Virtual    2304 768".  Those dimensions are not
big enough.  I now have "Virtual    2464 900" for that line, and I can
have these two displays at full resolution.


I don't know if this is a bug with the Display control panel, the
installer, some part of the X11 system, or a combination, but this
workaround worked for me.


-kb, the Kent who wishes others similarly good luck.


P.S.  I also messed around with "xrandr", it gave me key clues, but I
don't think it would have been necessary to fix this.