title: Problem with python versions and starting programs on Ubuntu 18.04
body: <p>A few days ago I had some issues with one program (adt from MGLTools) I was using without any problems for the last couple of months. I wanted to reinstall it (the latest version) and somehow it seems to me, that this messed up my python system I had on my Ubuntu 18.04 system. Or it might have even messed up some more things. I have to admit that I don't know that much about this whole system. Like which python version is used in which case, how it is accessed etc.</p>
  <p>Since then I had several issues also with other programs:
  If I want to run pymol, which took me 2 days to get running in the first place, I get this message:</p>
  <pre><code>Qt not available, using GLUT/Tk interface
  Traceback (most recent call last):
    File &quot;/usr/local/pymol-open-source/lib/python3.7/site-packages/pymol/__init__.py&quot;, line 73, in &lt;module&gt;
      pymol.launch(args)
    File &quot;/usr/local/pymol-open-source/lib/python3.7/site-packages/pymol/__init__.py&quot;, line 434, in launch
      _cmd.runpymol(None, block_input_hook)
  NotImplementedError: compile with --glut
  </code></pre>
  <p>I remember that it was quite difficult to get all the correct versions (python 3.7 and PyQt5) to be able to run the latest open source pymol. But at some point I got it working without any problems. And now even if I run python3.7 and type <code>import PyQt5</code> I don't get an error. So it seems that PyQt5 is working fine but maybe pymol is trying to use a different python version?</p>
  <p>Another program, which I could previously just start by typing <code>vmd</code> in my terminal, gave an error since it was not able to find the program. I could easily fix that by including the path in my bashrc file, but that was now necessary before.</p>
  <p>I know, that there are other ways besides the bashrc approach (<code>export PATH=$PATH:</code>) to start your program from the terminal and that there are things like system variables and system path but I'm completely unfamiliar with those and I'm afraid that my problem lies somewhere in that unfamiliar part.</p>
  <p>So I hope that some of you can give me a helping hand or any hint on where I could take a closer look to solve this issue. Your help is much appreciated ;-)</p>