Logging

Rails makes use of the ActiveSupport::Loggerclass to write log information. Other loggers, such as Log4r, may also be substituted.

• Configuration

  You can specify an alternative logger in config/application.rb  or any other environment file, for example:

  config.logger = Logger.new(STDOUT)
  config.logger = Log4r::Logger.new("Application Log")
  

  Or in the Initializer section, add any of the following

  Rails.logger = Logger.new(STDOUT)
  Rails.logger = Log4r::Logger.new("Application Log")
  

• Log Levels

  When something is logged, it's printed into the corresponding log if the log level of the message is equal to or higher than the configured log level. If you want to know the current log level, you can call the Rails.logger.level method.

  The available log levels are: :debug, :info, :warn, :error, :fatal, and :unknown, corresponding to the log level numbers from 0 up to 5, respectively. To change the default log level, use

  config.log_level = :warn # In any environment initializer, or
  Rails.logger.level = 0 # at any time
  

  This is useful when you want to log under development or staging without flooding your production log with unnecessary information.

• Writing Log Messages

  To write in the current log use the logger.(debug|info|warn|error|fatal|unknown) method from within a controller, model, or mailer:

  logger.debug "Person attributes hash: #{@person.attributes.inspect}"
  logger.info "Processing the request..."
  logger.fatal "Terminating application, raised unrecoverable error!!!"
  

• Tagged Logging

  When running multi-user, multi-account applications, it's often useful to be able to filter the logs using some custom rules. TaggedLoggingin Active Support helps you do exactly that by stamping log lines with subdomains, request ids, and anything else to aid debugging such applications.

  logger = ActiveSupport::TaggedLogging.new(Logger.new(STDOUT))
  logger.tagged("BCX") { logger.info "Stuff" }                            # Logs "[BCX] Stuff"
  logger.tagged("BCX", "Jason") { logger.info "Stuff" }                   # Logs "[BCX] [Jason] Stuff"
  logger.tagged("BCX") { logger.tagged("Jason") { logger.info "Stuff" } } # Logs "[BCX] [Jason] Stuff"