What is process "/usr/bin/X :0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch -background none"?

Solution 1:

This is the system graphics server and should not be killed. It converts the layout of desktop applications into low-level drawing operations on your graphics card, and routes keyboard and mouse input to the correct application that should receive them.

The reference to LightDM is that this is the first client it starts (the Ubuntu login screen); the reference to tcp is because X is designed to be network-transparent - it can work quite happily with input devices, applications and display devices all running on different computers. (I think that in Ubuntu it is configured not to accept network connections, only those coming through SSH, but may be wrong).

Check the statistics you are using are for X itself rather than X and children, since the children include all applications you run in a graphical environment. Excess resource usage by X itself is usually down to misbehaving desktop applications, but this can be very hard to debug.

Solution 2:

That's the X server. That's the graphical interface of which all other graphical applications are clients to.

• Yes it's supposed to run all the time.
• LightDM is just the login manager that loads first
• Using a lot of resources is usually a sign that X is either struggling with a crappy driver or that there's a crappy application (historically usually Compiz) trying to push a driver too hard.
• Using xorg-edgers is a good way to run crappy untested software. Read the PPA description and decided if you want to use ppa-purge. The newest nvidia drivers can be installed without upgrading X.