Strangely, this environment variable does not seem to be documented at
all:
hubot$ git grep HUBOT_LOG_LEVEL
src/robot.coffee: @logger = new Log process.env.HUBOT_LOG_LEVEL or 'info'
repositories (e.g. to link to private issues or commits), you need to
set `HUBOT_GITHUB_TOKEN` to your [OAuth token][token].
+If things aren't working as you'd expect, you can crank up the logging
+with `HUBOT_LOG_LEVEL=debug` (see [robot.coffee][]).
+
[hubot]: https://github.com/github/hubot
[hubot-irc]: https://github.com/nandub/hubot-irc
[scripts]: https://github.com/github/hubot-scripts/tree/master/src/scripts
[redis-brain]: https://github.com/github/hubot-scripts/blob/master/src/scripts/redis-brain.coffee
[redis]: ../redis/
[token]: https://help.github.com/articles/creating-an-access-token-for-command-line-use
+[robot.coffee]: https://github.com/github/hubot/blob/master/src/robot.coffee