Log levels

From 0 to 5 in severity:

  • debug - for debugging purposes, only
  • info - an informative message
  • warn - this may or may not be an issue
  • error - this is an issue, but the application can continue running
  • fatal - this is and issue, and the application should halt
  • unknown - we don’t know (?)

A corresponding Rails.logger.level method exists for each of these levels.

Logging important events in the application

When writing to the log, give the developer some “breadcrumbs” to follow. Specify the class name and method name that is writing to the log.

msg = "[#{self.class.name}##{__method__}] something important happened that we should log."

If you are rescueing, it probably makes sense to log the error, as well.

  # some code that might fail
rescue StandardError => err
  Rails.logger.error("[#{self.class.name}##{__method__}] raised an error.")
  # handle the error

Download logs from a remote source using Secure Copy (scp)

$ scp -p username@hostname:~/path/to/log/* ~/path/to/log

Searching Logs

The following command will show you three lines before and three lines after any occurrence of ClassName.

$ cat production.log | grep -B 3 -A 3 "ClassName"