I get an Input/Output error when trying to install a VOLTTRON agent - python-wheel

Question

SSH into a VOLTTRON instance, installing agents works. Log out, log back in and installing results in the following error:
2016-09-13 11:46:24,409 () volttron.platform.vip.agent.subsystems.rpc ERROR: unhandled exception in JSON-RPC method 'install_agent':
Traceback (most recent call last):
File "/home/volttron/volttron/volttron/platform/vip/agent/subsystems/rpc.py", line 168, in method
return method(*args, **kwargs)
File "/home/volttron/volttron/volttron/platform/control.py", line 287, in install_agent
agent_uuid = self._aip.install_agent(path, vip_identity=vip_identity)
File "/home/volttron/volttron/volttron/platform/aip.py", line 296, in install_agent
unpack(agent_wheel, dest=agent_path)
File "/home/volttron/volttron/env/local/lib/python2.7/site-packages/wheel/tool/__init__.py", line 135, in unpack
sys.stderr.write("Unpacking to: %s\n" % (destination))
IOError: [Errno 5] Input/output error

Answer 1

When any background process is disowned, the ssh session is terminated, stdeff and stdout are not redirected to /dev/null, and the process tries to write to either it results in an IOError.
In this case one of the third party libraries that VOLLTRON uses when installing an agent tries to write to stderr (much to our chagrin). Even if the platform is run with the -l option it will still occasionally write to stderr. Unfortunately there is no reliable way for VOLTTRON to do the right thing with stderr in all cases so we have to leave it up to the user to know when they need to redirect output to /dev/null.
To run in the background use start-stop-daemon which automatically redirects everything to /dev/null or use this command to start the platform:
volttron -vv -l volttron.log > /dev/null 2>&1&
You can then safely disown the process and logout. Installations will still work.