Note libGL.so as a prerequisite for running on Linux

[j4yk]

I would open a pull request myself, but I am not sure where this information would fit best.

Here is the problem:
On a fresh, headless Linux system that should put the Squeak window up on an external X server (that is, headless Linux-VMs, or running Linux-Squeak on the Windows subsystem for Linux), the squeak.sh script might complain as follows:

$ ./squeak.sh
Using ..../bin/squeak...
could not find display driver vm-display-X11; either:
  - check that ..../bin//vm-display-X11.so exists, or
  - use the '-plugins <path>' option to tell me where it is, or
  - remove DISPLAY from your environment.
Aborted (core dumped)

The vm-display-X11.so file is there, but it might be missing libGL.so to be loaded:

$ ldd bin/vm-display-X11.so
        linux-vdso.so.1 =>  (0x00007fffc414a000)
        libGL.so.1 => not found
        libXext.so.6 => /usr/lib/x86_64-linux-gnu/libXext.so.6 (0x00007fb20b2b0000)
        libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fb20b080000)
        ...

So, on Ubuntu, the solution is to install the libgl1-mesa-glx package. This information can be dug from the mailing list, but it is a hassle to do so every time, since it is not the first seach result you get. Could we put the information up somewhere on the website?

[fniephaus]

Maybe we should add a check to the squeak.sh file in https://github.com/squeak-smalltalk/squeak-app instead?

[j4yk]

Maybe. Looks like the squeak.sh is rather part of the VM builds, isn't it? https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/platforms/unix/config/squeak.sh.in
I have no experience with running a headless Squeak, maybe it should be checked whether it needs the graphics libraries anyway.

[krono]

This is now related to #43