Qt: can't find -lGL error

You should install package "libgl1-mesa-dev":

sudo apt install libgl1-mesa-dev

you don't need to install anything. libGL is already installed with Ubuntu, you just need to soft link it. (tested for ubuntu 14.x and 15.x, might work for later versions)

1. First locate the GL library
2. Then link it under /usr/lib
3. If the library is missing, it can be installed via libgl1-mesa-dev package

Here is how you could do this:

$ locate libGL
/usr/lib/i386-linux-gnu/mesa/libGL.so.1
/usr/lib/i386-linux-gnu/mesa/libGL.so.1.2.0
/usr/lib/x86_64-linux-gnu/libGLEW.so.1.10
/usr/lib/x86_64-linux-gnu/libGLEW.so.1.10.0
/usr/lib/x86_64-linux-gnu/libGLEWmx.so.1.10
/usr/lib/x86_64-linux-gnu/libGLEWmx.so.1.10.0
/usr/lib/x86_64-linux-gnu/libGLU.so.1
/usr/lib/x86_64-linux-gnu/libGLU.so.1.3.1
/usr/lib/x86_64-linux-gnu/mesa/libGL.so.1
/usr/lib/x86_64-linux-gnu/mesa/libGL.so.1.2.0
/usr/lib/x86_64-linux-gnu/mesa-egl/libGLESv2.so.2
/usr/lib/x86_64-linux-gnu/mesa-egl/libGLESv2.so.2.0.0
$ sudo ln -s /usr/lib/x86_64-linux-gnu/mesa/libGL.so.1 /usr/lib/libGL.so

The gui Qt module is included by default. If you don't want to use it in a project (e.g., it is a library or only uses stdio), you need to specify that in the .pro file.

QT -= gui

And the linker won't attempt to find lGL regardless of whether it is installed.

My case is admittedly a bit odd, since the main reason to use Qt is to create gui's. Installing the GL library is certainly not difficult, I just wanted to know why my quick and dirty Hello World wanted it.