Mon Aug 31 23:50:39 CEST 2015

application private directory

Diving into OTP/rebar due to Cowyboy.
What is "an application's private directory"?
And why do I get the error:

{reason,{badarg,"Can't resolve the priv_dir of application erws"}}

Let's look in the source

=> {error,bad_name}

Because you most likely don't use releases or set ERL_LIBS like you should. Cowboy stopped guessing, it caused other issues.
[1] https://github.com/ninenines/cowboy/issues/613