Starting background tasks with Capistrano

Question

For my RubyOnRails-App I have to start a background job at the end of Capistrano deployment. For this, I tried the following in deploy.rb:

run "nohup #{current_path}/script/runner -e production 'Scheduler.start' &", :pty => true

Sometimes this works, but most of the time it does not start the process (= not listed in ps -aux). And there are no error messages. And there is no nohup.out, not in the home directory and not in the rails app directory.

I tried using trap('SIGHUP', 'IGNORE') in scheduler.rb instead of nohup, but the result is the same.

The only way to get it work is removing the ":pty => true" and do a manual Ctrl-C at the end of "cap deploy". But I don't like this...

Are there any other chances to invoke this Scheduler.start? Or to get some more error messages?

I'm using Rails 2.3.2, Capistrano 2.5.8, Ubuntu Hardy on the Server

Answer 1

With :pty => true, user shell start-up scripts (e.g. bashrc, etc.) are (usually) not loaded. My ruby program exited right after launching because of the lack of dependent environment variables.

Without :pty => true, as you described in the question, capistrano hangs there waiting for the process to exit. You'll need to redirect both stdout and stderr to make it return immediately.

run 'nohup ruby -e "sleep 5" &' # hangs for 5 seconds
run 'nohup ruby -e "sleep 5" > /dev/null &' # hangs for 5 seconds
run 'nohup ruby -e "sleep 5" > /dev/null 2>&1 &' # returns immediately. good.

If your background task still doesn't run. Try redirecting stdout and stderr to a log file so that you can investigate the output.