CQ5 logging

This week I held a workshop at a customer and someone asked me “How do other customers of Day handle their logfiles? Do they check them and analyze the logfiles?” I had to admit that “according to my experience nobody really cares about them. The only situation they care about them is when the disk is full f them.” Yeah, a sad truth.

But this brings us to todays topic: Logfiles and keeping track of them. CQ5 is by default pretty noisy; if you check the file crx-quickstart/logs/error.log after some requests have been made, you see a lot of messages of loglevel “INFO”. Yes, sometimes quite interesting, but in the end they pollute the log and the real important messages vanish in the pure mass of these noise. So, at least for production systems, the loglevel should incrased to WARN or even “ERROR”, so only logs at level WARN or ERROR are logged, INFO is supressed.

So, how can this be achieved? Sling as part of the WCM part of CQ5 brings its own logging, it can be configured using the Felix console and is well documented on the Day documentation site. CRX (at least up to CRX 2.1) does have its own logging mechanisms (log4j), which can be reconfigured in the crx-quickstart/server/runtime/0/_crx/WEB-INF/log4j.xml file.

And, on top of this all, we have on a standard Unix system

  • crx-quickstart/logs/stderr.log and crx-quickstart/logs/stdout.log
  • crx-quickstart/logs/server.log
  • crx-quickstart/server/logs/startup.log

neat, isn’t it? Ok, how can you configure them?

Short answer: you can’t. At least it isn’t documented.

The stdout.log and stderr.log and the standard output and standard error channel of the java process, which is redirected to these files. Especially stdout.log fills up pretty fast, because CRX logs all its messages also to the stdout. So fixing up the log4j.xml file is mandatory, because we don’t need this information twice in the crx/error.log and the stdout.log file. Oh, and of course these files aren’t rotated, but new data is appended only. So it grows and grows and grows.

The server.log file is written by the CQSE servlet engine and cleared when the servlet engine is started. Same as for the startup.log, which contains the output of the serverctl script before starting the java and also error messages, if the java process doesn’t start at all (most times due to invalid parameters).

A few recommendations (just a personal point of view):

  • Log rotation should be performed on a timely basis and not be based on the size of the logfile. You should have enough space then and monitor it closely, of course. But this helps you to lookup a certain problem (“Wait, it was yesterday, so it must be in error.log.0 file”) without hassles.
  • implement your own logfile rotation for the stdout.log and stderr.log files. I fill a bug for it too, but till then you need to help yourself. Sorry.
  • Increase loglevel to WARN. INFO just logs too much noise.
  • Adjust the log4j.xml of CRX and change it to something like this:
 <level value="warn" />
 <appender-ref ref="error"/>

So adjusting the logging according to your needs shows, that you care about them and know, that they are useful at all. Which is a required step to do some analysis on them. But that topic is a candidate for one of the next postings.