Question: Following is link to my init script for unicorn.
<https://gist.github.com/1466775>

Restart command has never worked for me. I am using upgrade to restart unicorn after each deploy. But whenever there is major changes like new gems being added, upgrade won't work. Recently, i replaced hoptoad gem with airbrake and it errors out saying 'uninitialized constant Airbrake (NameError)'. But when i stopped and started unicorn again, it worked fine. Does the problem lies in init script or its different problem?

Thanks.

Answer: 
According to your init script, "/bin/init.d/unicorn restart" sends HUP signal to unicorn master process

------cropped

```
restart|reload)
    sig HUP && echo reloaded OK && exit 0
    echo >&2 "Couldn't reload, starting '$CMD' instead"
    su - $USER -c "$CMD"

```

-----cropped

This is what HUP does to unicorn process :

reloads config file and gracefully restart all workers. If the “preload\_app” directive is false (the default), then workers will also pick up any application code changes when restarted. If “preload\_app” is true, then application code changes will have no effect.

What you are looking for is USR2 signal which your upgrade parameter to unicorn is already doing !

USR2 signal re-executes the running binary. A separate QUIT should be sent to the original process once the child is verified to be up and running.
I had a very similar problem and finally [found the solution](http://blog.willj.net/2011/08/02/fixing-the-gemfile-not-found-bundlergemfilenotfound-error/)

I had looked through the logs before but obviously failed to see the `(Bundler::GemfileNotFound)` error. Turns out there are old references to earlier releases and once the gem file changes, the new master silently fails. Tail -f your unicorn log to see what happens. My issues were all fixed as per the link with the following in my unicorn.rb

```
 before_exec do |server|
    ENV['BUNDLE_GEMFILE'] = "#{root}/Gemfile"
 end 

```