Just upgraded to Rails 4.2 and I get Internal Server Error on localhost and in production when trying to edit a model with multiple has_many objects. This is the message I see on the rails s console
!! Unexpected error while processing request: Too many open files - Maximum file multiparts in content reached
The request does not even get to the controller i.e., I DO NOT see the usual following lines in rails s console
Started GET "/feeds/3/edit" for 127.0.0.1 at 2015-01-04 20:07:19 -0800
Processing by FeedsController#edit as HTML
......
......
Any clues?? Using Ruby 2.1.5 upgraded to 2.2 with no luck.
It looks like the multipart limit was added in the Rails 4.2 version of Rack (https://github.com/rack/rack/commit/b0b5fb9467e6ed777d3eaf35afc81d758e308aab). The default is 128, which may be too little for your purposes, it was for mine. Setting the value to 0 in an initializer removes the limit and fixes the problem:
Rack::Utils.multipart_part_limit = 0
I would suggest tailoring the value until it fits your needs so your server doesn't run out of file handles. My app uses a massive form and setting it to 512 seemed to work for me.