Minimal Dockerfile to reproduce supervisor "CRIT uncaptured python exception, closing channel"

Dockerfile

FROM ubuntu:16.04

# this will install the latest supervisor from pip (at the time of writing that would be supervisor-3.3.1)
RUN apt-get update && apt-get install -y -q locales python-pip && pip install supervisor && \
    echo "[supervisord]\nnodaemon=true\n\n[program:cause-error]\ncommand=/bin/bash -c 'echo Test'\nstdout_logfile=/dev/stdout" > /etc/supervisord.conf

CMD /usr/local/bin/supervisord

log

# docker run db6f
/usr/local/lib/python2.7/dist-packages/supervisor/options.py:298: UserWarning: Supervisord is running as root and it is searching for its configuration file in default locations (including its current working directory); you probably want to specify a "-c" argument specifying an absolute path to a configuration file for improved security.
  'Supervisord is running as root and it is searching '
2017-05-17 12:20:26,842 CRIT Supervisor running as root (no user in config file)
2017-05-17 12:20:26,845 INFO supervisord started with pid 7
2017-05-17 12:20:27,848 INFO spawned: 'cause-error' with pid 10
Test
2017-05-17 12:20:27,860 CRIT uncaptured python exception, closing channel <POutputDispatcher at 140178721855392 for <Subprocess at 140178721855248 with name cause-error in state STARTING> (stdout)> (<type 'exceptions.IOError'>:[Errno 29] Illegal seek [/usr/local/lib/python2.7/dist-packages/supervisor/supervisord.py|runforever|227] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|handle_read_event|232] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|record_output|166] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|_log|142] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|info|275] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|log|293] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|emit|186] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|doRollover|211])
2017-05-17 12:20:27,860 INFO exited: cause-error (exit status 0; not expected)
2017-05-17 12:20:28,863 INFO spawned: 'cause-error' with pid 11
Test
2017-05-17 12:20:28,873 CRIT uncaptured python exception, closing channel <POutputDispatcher at 140178721856040 for <Subprocess at 140178721855248 with name cause-error in state STARTING> (stdout)> (<type 'exceptions.IOError'>:[Errno 29] Illegal seek [/usr/local/lib/python2.7/dist-packages/supervisor/supervisord.py|runforever|227] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|handle_read_event|232] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|record_output|166] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|_log|142] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|info|275] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|log|293] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|emit|186] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|doRollover|211])
2017-05-17 12:20:28,874 INFO exited: cause-error (exit status 0; not expected)
2017-05-17 12:20:30,879 INFO spawned: 'cause-error' with pid 12
Test
2017-05-17 12:20:30,891 CRIT uncaptured python exception, closing channel <POutputDispatcher at 140178721930632 for <Subprocess at 140178721855248 with name cause-error in state STARTING> (stdout)> (<type 'exceptions.IOError'>:[Errno 29] Illegal seek [/usr/local/lib/python2.7/dist-packages/supervisor/supervisord.py|runforever|227] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|handle_read_event|232] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|record_output|166] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|_log|142] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|info|275] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|log|293] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|emit|186] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|doRollover|211])
2017-05-17 12:20:30,891 INFO exited: cause-error (exit status 0; not expected)
2017-05-17 12:20:33,897 INFO spawned: 'cause-error' with pid 13
Test
2017-05-17 12:20:33,906 CRIT uncaptured python exception, closing channel <POutputDispatcher at 140178721855680 for <Subprocess at 140178721855248 with name cause-error in state STARTING> (stdout)> (<type 'exceptions.IOError'>:[Errno 29] Illegal seek [/usr/local/lib/python2.7/dist-packages/supervisor/supervisord.py|runforever|227] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|handle_read_event|232] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|record_output|166] [/usr/local/lib/python2.7/dist-packages/supervisor/dispatchers.py|_log|142] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|info|275] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|log|293] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|emit|186] [/usr/local/lib/python2.7/dist-packages/supervisor/loggers.py|doRollover|211])
2017-05-17 12:20:33,906 INFO exited: cause-error (exit status 0; not expected)
2017-05-17 12:20:33,906 INFO gave up: cause-error entered FATAL state, too many start retries too quickly