For the OP this was a matter of insufficient permissions, but I am trying to package a rails app in a nix package. Nix packages are created in a read-only fs for security and enforcement of conventions. I can set the rails log and tmp/* dirs at the command line to /var/lib/… but under no circumstances will a mkdir in the package (container) work. for some reason railties/lib/rails/commands/server/server_command.rb has a mandatory mkdir and no error handling, so when I try to start the server (even though I've remapped the tmp and log dirs) it still tries to create these subdirs. When it fails, the server exists with an error. I can comment out line 35 of server_commmand.rb and everything is peachy, but clearly that's not production safe. I've also tried monkey patching RailsServer but there is a dependency tree issue that is too deep rooted to be safe for production use. I am hoping one of you clever wizards knows something that I don't that will make it possible to run a rails server on