I am trying to install redmine (which is a ruby app ) in my arch system. But I am not able to fire up the app as it gives me the error for phusion passenger.

I am trying to install redmine (which is a ruby app ) in my arch system. But I am not able to fire up the app as it gives me the error for phusion passenger.

Looks like you have something mis-configured in your Apache setup which is pointing to the path /srv/http -or- you don't have something configured which would've built out the path /srv/http/config.
I'd take a look at this Howto/Guide from the ArchLinux wiki on setting up Redmine.