X11/Xlib.h not found in Ubuntu

Presume he's using the tutorial from http://www.arcsynthesis.org/gltut/ along with premake4.3 :-)

sudo apt-get install libx11-dev ................. for X11/Xlib.h
sudo apt-get install mesa-common-dev........ for GL/glx.h
sudo apt-get install libglu1-mesa-dev ..... for GL/glu.h
sudo apt-get install libxrandr-dev ........... for X11/extensions/Xrandr.h
sudo apt-get install libxi-dev ................... for X11/extensions/XInput.h

After which I could build glsdk_0.4.4 and examples without further issue.

A quick search using...

apt search Xlib.h

Turns up the package libx11-dev but you shouldn't need this for pure OpenGL programming. What tutorial are you using?

You can add Xlib.h to your system by running the following...

sudo apt install libx11-dev

Why not try find /usr/include/X11 -name Xlib.h

If there is a hit, you have Xlib.h

If not install it using sudo apt-get install libx11-dev

and you are good to go :)