Here’s a fun error I kept knocking up against when trying to run migrations, rake tasks, or script/console on a server here. Before you start uninstalling gems, reinstalling ruby, etc. check and see if you are on a CPanel server. If you are, most likely shell fork bomb protection is enabled in CPanel’s WHM. Shell fork bomb protection severely limits the amount of memory that shell users can access. Unfortunately that protection can prevent you from running legitimate processes, like rake tasks.

If you are the admin of the server, just log into the WHM, and disable shell fork bomb protection, then open a new shell and try your commands again. You do need to log out of the shell and open a new shell for the SFBP restriction to be lifted.

Of course, if you are on a shared server and not the admin, you might be out of luck. It’s doubtful that the server admin will disable this protection since it does serve a useful function, mainly preventing users from running reckless scripts that could take the whole server down. I haven’t looked into it, but there may be a way to configure CPanel to allow a higher limit, or opt-out certain users.

passenger-memory-stats

This tool allows you to see a display of the real-time memory usage for Passenger and Apache.

passenger-status

This tool shows you what your current passenger stats are and what apps are currently running.

You can read more about both of these in the Passenger documention.