Process Forking

In Ruby it is common for Frameworks such Puma and Resque to fork a copy of the process so that it can run independently from the parent process.

After a process has forked SemanticLogger.reopen must be called to re-open files and re-start the appender thread. Otherwise, logging will appear to stop.

Below are some of the common frameworks that use process forking and what you need to do so that Semantic Logger can continue to function after a fork:


With Unicorn, add the following code to you Unicorn configuration:

# config/unicorn.conf.rb
after_fork do |server, worker|
  # Re-open appenders after forking the process


If running Puma 2 in Clustered mode and you’re preloading your application, add the following to your worker boot code:

# config/puma.rb
on_worker_boot do
  # Re-open appenders after forking the process

Auto-detected Frameworks

The following frameworks are automatically detected by the Rails Semantic Logger gem, so the custom code below is only necessary when using Semantic Logger stand-alone:

Add the following code only if Rails Semantic Logger gem is not being used and you are using these frameworks:

# Passenger provides the :starting_worker_process event for executing
# code after it has forked, so we use that and reconnect immediately.
if defined?(PhusionPassenger)
  PhusionPassenger.on_event(:starting_worker_process) do |forked|
    ::SemanticLogger.reopen if forked

# Re-open appenders after Resque has forked a worker
if defined?(Resque)
  Resque.after_fork { |job| ::SemanticLogger.reopen }

# Re-open appenders after Spring has forked a process
if defined?(Spring)
  Spring.after_fork { |job| ::SemanticLogger.reopen }

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