While I've been vaguely aware of this myself for a few years, what motivates my present interest are the two, following unsettling situations.
First, when I go to tailor monitor settings on Maverick Meerkat (System -> Preferences -> Monitors), I cannot. I get an alert to the effect that Linux...
Could not get screen information
RANDR extension is not present
And every time I launch gvim (and also gedit) from the command line, I get (the warning):
Xlib: extension "RANDR" missing on display ":0.0".
Fortunately, my favorite program editor and text processor still works, but I have to admit that the warning has grown old and very annoying.
I've seen these (well, the second example, anyway) before on other systems, perhaps on openSuSE back in the day and I had to ignore them without ever figuring out what to do.
Xinerama and RANDR
What I gather from reading the mostly speculative discussions is that these two are incompatible. Some say to disable Xinerama, but if you're using NVIDIA drivers, you're stuck because without it, it would appear, you cannot configure multiple monitor support in the way I like it: mapping two edge-to-edge for maximum real estate.
russ@russ-elite-book:/etc/X11> fgrep inerama xorg.conf
# Removed Option "Xinerama" "0"
Option "Xinerama" "1"
Option "TwinViewXineramaInfoOrder" "CRT-0"
What I think is happening in the second example is that an application that opens a GUI appeals to X11 for something that it cannot provide because to have Xinerama enabled is to have RANDR blocked. I've checked with the Synaptic Package Manager to see that both are present on my host. Indeed, both appear to be there:
russ@russ-elite-book:~> ll /usr/lib/libXrandr*
lrwxrwxrwx [...] /usr/lib/libXrandr.so.2 -> libXrandr.so.2.2.0
-rw-r--r-- [...] /usr/lib/libXrandr.so.2.2.0
After so many years, you'd think those who actually know what's going on would, if not in a position in the Linux development ranks or the driver suppliers, simply issue a wiki or other form of explanation as to what's going on and clearly state the choices of action and consequences of adopting each choice.
Well, it's what I'd do. But then, my goal is always to fan away the smoke that encircles those people and technologies waving magic wands and crowned with pointy, black hats emblazoned with moons and stars.