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I have a custom daemon that is managed by upstart on my Ubuntu server. It works perfectly except that I need to capture (log) the daemon's output. The official stanzas page says that I can use console logged to do this, but what file does it log to?

I've also read that console logged is no longer a valid stanza. I'm currently using 0.3.9 (Hardy) but will upgrade to 0.6.x (Lucid) in a few months. If console logged in fact won't work with later versions, what do I use instead?

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Can you simply update your custom daemon to send the output to syslog, or to a logfile specified in the daemon's configuration file? –  Zoredache Feb 18 '10 at 2:22
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4 Answers

This snippet will pipe the output of your service into logger, while still allowing you to exec the service process (thus replacing the shell process) so that upstart doesn't get confused. It also makes sure the logger process is reparented to init, so it's not a child of your service, and it avoids leaving cruft sitting around in the filesystem, even though it needs to create a fifo temporarily.

script
  mkfifo /tmp/myservice-log-fifo
  ( logger -t myservice </tmp/myservice-log-fifo & )
  exec >/tmp/myservice-log-fifo
  rm /tmp/myservice-log-fifo
  exec myservice 2>/dev/null
end script

Here's how it works:

  1. mkfifo /tmp/myservice-log-fifo simply makes the fifo special file (aka named pipe). Type man 7 fifo for more info.
  2. ( logger ... </tmp/myservice-log-fifo & ) starts logger reading from the fifo, in the background. The parens cause the logger process to be reparented to init, rather than remaining a child of the current shell process.
  3. exec >/tmp/myservice-log-fifo redirects the current shell's stdout to the fifo. Now we have an open file descriptor for that fifo, and we don't actually need the filesystem entry any more...
  4. rm /tmp/myservice-log-fifo so we'll remove it.
  5. exec myservice 2>/dev/null simply runs the service in the usual way. Stdout is already going to the fifo, and that won't change when the new program executes.

UPDATE: set -e is not needed as Upstart runs scripts with this option by default (see http://upstart.ubuntu.com/cookbook/#develop-scripts-using-bin-sh)

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great answer, and doesn't leave fifo files lying around anywhere. –  Ash Berlin Mar 29 '12 at 12:25
    
What is the set -e? –  Peter Mounce Sep 24 '12 at 22:23
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The set -e causes the script to exit immediately if any command fails. Without that line, the script would continue running subsequent commands uselessly (and possibly dangerously). –  Keith Rarick Oct 13 '12 at 23:53
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This is ugly but so far the best I have found

exec /path/to/server >> /tmp/upstart.log 2>&1

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You can also redirect the output to syslog, e.g.

exec $SERVER 2>&1 | logger -t myservice -p local0.info

However, the pipeline may cause upstart to confuse the PID of the logging process with the PID of the daemon.

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The daemon confusing the PID is actually a useless daemon, since it is supposed to watch the process, respawn it then. Any idea on how to make sure the right PID is being watched? –  Johann Philipp Strathausen Feb 10 '12 at 11:04
    
I think (but haven't tried) that you'll want the expect fork or expect daemon stanza. Or you could cat the pid-file into the log message otherwise, I guess. –  Peter Mounce Jun 20 '12 at 12:45
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If you use the console output stanza, and then pipe your script's output to logger (the shell command interface to the syslog(3) system log module) then that will work.

For example

console output
exec /my/script | logger

will log to /var/log/messages

For example

console output
exec /my/script | logger -t my-script

will log to /var/log/messages and tag each message with my-script

logger --help for logger usage options.

(I'm on the Amazon Linux AMI, which is Centos 5.x based; YMMV)

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