title: graphviz.backend.ExecutableNotFound: failed to execute ['dot', '-Tpng'], make sure the Graphviz executables are on your systems' PATH
body: <p>I wasn't able to find any solution to this issue for one hour and decided better to ask here. The only rich info is given <a href="https://stackoverflow.com/questions/35064304/runtimeerror-make-sure-the-graphviz-executables-are-on-your-systems-path-aft">here</a> with no detailed instructions to match my case.</p>
  
  <p>I am on Windows 10, using PyCharm to connect to offline Ubuntu 16.04 server to try some machine learning classification.</p>
  
  <p>The code is working to some point, then throwing this</p>
  
  <pre><code>Traceback (most recent call last):
    File "/home/user/.local/lib/python3.5/site-packages/graphviz/backend.py", line 159, in run
      proc = subprocess.Popen(cmd, startupinfo=get_startupinfo(), **kwargs)
    File "/usr/lib/python3.5/subprocess.py", line 947, in __init__
      restore_signals, start_new_session)
    File "/usr/lib/python3.5/subprocess.py", line 1551, in _execute_child
      raise child_exception_type(errno_num, err_msg)
  FileNotFoundError: [Errno 2] No such file or directory: 'dot'
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "/home/user/project/2_input/xgboost_loop.py", line 55, in &lt;module&gt;
      xgb.plot_tree(classifier, ax=plt.gca())
    File "/home/user/.local/lib/python3.5/site-packages/xgboost/plotting.py", line 281, in plot_tree
      s.write(g.pipe(format='png'))
    File "/home/user/.local/lib/python3.5/site-packages/graphviz/files.py", line 138, in pipe
      quiet=quiet)
    File "/home/user/.local/lib/python3.5/site-packages/graphviz/backend.py", line 229, in pipe
      out, _ = run(cmd, input=data, capture_output=True, check=True, quiet=quiet)
    File "/home/user/.local/lib/python3.5/site-packages/graphviz/backend.py", line 162, in run
      raise ExecutableNotFound(cmd)
  graphviz.backend.ExecutableNotFound: failed to execute ['dot', '-Tpng'], make sure the Graphviz executables are on your systems' PATH
  
  Process finished with exit code 1
  </code></pre>
  
  <p>I checked  via <code>pip list</code> that I do have <code>graphviz</code> version <code>0.13.2</code> on Ubuntu server. One suggested in the above given link that  the output of <code>whereis dot</code> should be added as <code>os.environ["PATH"] += os.pathsep + 'OUTPUT'</code> to the file to be run, but there isn't any output except <code>dot:</code>.</p>
  
  <p>Locally, I also checked that I have the same <code>graphviz</code> version <code>0.13.2</code>.</p>