subprocess.CalledProcessError: returned non-zero exit status 0 <p>What is the meaning of this paradoxical error?</p> <blockquote> <p>subprocess.CalledProcessError: Command '/home/travis/build/fritzo/pomagma/build/debug/src/cartographer/cartographer' returned non-zero exit status 0</p> </blockquote> <p>It happens when I start a subprocess, then tell that subprocess to cleanly exit via a zmq socket. It appears that while zmq is polling, the process exits cleanly (exit code 0), and then this error is raised.</p> <p>Here's the whole traceback (from a <a href="https://travis-ci.org/fritzo/pomagma/builds/123794173" rel="nofollow">travis log</a>):</p> <pre><code>Traceback (most recent call last): File "/home/travis/virtualenv/python2.7_with_system_site_packages/bin/pomagma.make", line 9, in &lt;module&gt; load_entry_point('pomagma==0.2.8', 'console_scripts', 'pomagma.make')() File "/home/travis/virtualenv/python2.7_with_system_site_packages/local/lib/python2.7/site-packages/parsable.py", line 181, in dispatch dispatch(argv) File "/home/travis/virtualenv/python2.7_with_system_site_packages/local/lib/python2.7/site-packages/parsable.py", line 129, in dispatch parser(*args, **kwargs) File "/home/travis/virtualenv/python2.7_with_system_site_packages/local/lib/python2.7/site-packages/parsable.py", line 64, in parser fun(*typed_args, **typed_kwargs) File "/home/travis/build/fritzo/pomagma/pomagma/make.py", line 130, in test_atlas _test_atlas(theory) File "/home/travis/build/fritzo/pomagma/pomagma/make.py", line 59, in _test_atlas assert actual_size == expected_size File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__ self.gen.next() File "/home/travis/build/fritzo/pomagma/pomagma/cartographer/__init__.py", line 14, in load client.stop() File "/home/travis/build/fritzo/pomagma/pomagma/cartographer/client.py", line 207, in stop self._call(request) File "/home/travis/build/fritzo/pomagma/pomagma/cartographer/client.py", line 35, in _call self._poll_callback() File "/home/travis/build/fritzo/pomagma/pomagma/cartographer/server.py", line 66, in check self.log_error() File "/home/travis/build/fritzo/pomagma/pomagma/cartographer/server.py", line 73, in log_error raise CalledProcessError(self._proc.poll(), BINARY) subprocess.CalledProcessError: Command '/home/travis/build/fritzo/pomagma/build/debug/src/cartographer/cartographer' returned non-zero exit status 0 </code></pre>