Yes, it is possible. I do it for games.
xinit session -- :1 -xf86config config.conf
Where session should be replaced by the session you'd like to start in the new Xorg display, and config.conf is the configuration file.
For starting it automatically, take a look at this answer.
I started answering this (as I do when I start answering a lot of questions on AU) because I wanted to know more. You've asked some pretty decent questions about how things work that I confess, I didn't immediately have answers to. I've done my best.
You'll understand what I'm talking about when you look at man xorg.conf and find things like this:
VIDEOADAPTOR SECTION
Nobody wants to say how this works. Maybe nobody knows ...
Seriously.
LightDM is started by Upstart (the init system, started by the Kernel on boot) here:
/etc/init/lightdm.conf
That feeds into the lightdm command which reads (seat information, etc) from:
/etc/lightdm/lightdm.conf
/etc/lightdm/lightdm.conf.d/*
And then starts X which looks for the following configurations:
/etc/X11/<cmdline>
/usr/etc/X11/<cmdline>
/etc/X11/$XORGCONFIG
/usr/etc/X11/$XORGCONFIG
/etc/X11/xorg.conf
/etc/xorg.conf
/usr/etc/X11/xorg.conf.<hostname>
/usr/etc/X11/xorg.conf
/usr/lib/X11/xorg.conf.<hostname>
/usr/lib/X11/xorg.conf
/etc/X11/xorg.conf.d/*
/usr/etc/X11/xorg.conf.d/*
If present in the configuration, that's how X would pick the driver/monitor/etc layout... If it's not, the newer XRandR extensions have a major part to play in guessing and persisting monitor settings.
If you don't want a best guess, you can force it in a direction by:
But if you let xrandr handle things, once you log in, the configuration comes from:
~/.config/monitors.xml
After X starts there's a load of session gubbins (autostarts, etc) that start that aren't particularly relevant to the graphics process but they're probably worth mentioning. Mentioned.
There are two bits that elude proper explanation:
- The relationship between Xorg and Kernel drivers has made me go thoroughly cross-eyed. I found a very exhausti{ve,ng} book on the subject[PDF!] but haven't had the time to even scratch it.
- How Xorg/XRandr picks the right driver.
There's certainly a lot more automagical wrangling than there used to be.
Best Answer
X-Windows is a Unix/Linux Client-Server system. Although usually on the same computer, the Client and Server can be on different computers, unlike Microsoft Windows.
X11 is a network protocol. It encodes things such as graphic primitives, images, pointer motion, and key presses.
X clients are graphical applications like Firefox.
Xorg is an X server. It implements X11 and provides an interface to keyboards, mice, and video cards.
Gnome, KDE, LXDE, and Xfce are desktop environments. They provide libraries and specifications that applications use
When running X-Windows, instead of a console login, the Display Manager i.e. Lightdm starts up. The DM starts the X-server and asks for login credentials and then launches the user's desktop environment.
Hope that helps.