I can't install/uninstall a plugin, I get something about an "unexpected keyword argument 'async'"

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If you get something like this upon attempting to install or uninstall a plugin via OctoPrint's plugin manager or on attempting to perform an upgrade via OctoPrint's software update plugin:

2018-07-15 17:02:37,694 - octoprint.plugins.pluginmanager - ERROR - Could not install plugin from <url>
Traceback (most recent call last):
  File "/home/pi/OctoPrint/venv/lib/python2.7/site-packages/octoprint/plugins/pluginmanager/__init__.py", line 348, in command_install
    returncode, stdout, stderr = self._call_pip(pip_args)
  File "/home/pi/OctoPrint/venv/lib/python2.7/site-packages/octoprint/plugins/pluginmanager/__init__.py", line 652, in _call_pip
    return self._pip_caller.execute(*args)
  File "/home/pi/OctoPrint/venv/local/lib/python2.7/site-packages/octoprint/util/pip.py", line 172, in execute
    return self.call(command, **kwargs)
  File "/home/pi/OctoPrint/venv/local/lib/python2.7/site-packages/octoprint/util/commandline.py", line 83, in call
    p = sarge.run(command, **kwargs)
  File "/home/pi/OctoPrint/venv/local/lib/python2.7/site-packages/sarge/__init__.py", line 1462, in run
    p.run(input=input, async_=async_)
  File "/home/pi/OctoPrint/venv/local/lib/python2.7/site-packages/sarge/__init__.py", line 1071, in run
    self.run_node(node, input=input, async_=False)
  File "/home/pi/OctoPrint/venv/local/lib/python2.7/site-packages/sarge/__init__.py", line 1187, in run_node
    result = getattr(self, method)(node, input, async_)
  File "/home/pi/OctoPrint/venv/local/lib/python2.7/site-packages/sarge/__init__.py", line 1333, in run_command_node
    node.cmd.run(input=input, async_=async_)
  File "/home/pi/OctoPrint/venv/local/lib/python2.7/site-packages/sarge/__init__.py", line 655, in run
    self.process = p = Popen(self.args, **self.kwargs)
TypeError: __init__() got an unexpected keyword argument 'async'

then this is caused by a backwards incompatible version of the sarge dependency (version 0.1.5). You'll have to manually downgrade sarge to a compatible version (version 0.1.4). Assuming you installed OctoPrint into a venv located at /home/pi/OctoPrint (as visible in the log snippet above), do this:

  • Log into your OctoPrint server via SSH or via attached monitor & keyboard
  • source /home/pi/OctoPrint/venv/activate
  • pip install sarge==0.1.4
  • Restart OctoPrint

That should make everything work again. 1.3.9 will have a fix for this in place.

(If your OctoPrint installation path is a different one, substitute accordingly.)