title: *nix select and exceptfds/errorfds semantics
body: <p>The <a href="http://www.opengroup.org/onlinepubs/007908775/xsh/select.html" rel="noreferrer">select</a> syscall takes 3 filedescriptor sets for watching fds for readable/writeable and "exceptions" on filedescriptor.</p>
  
  <p>My select <a href="http://web.archive.org/web/20070710123713/http://man.netbsd.se/?find=select%202%2020" rel="noreferrer">man page</a> doesn't state much about the <code>exceptfd</code> descriptor set. What is it used for; what kind of exceptions can and will it notify on file descriptors?</p>
  
  <p>I'm assuming this can be different for the descriptor type... whether it's a TCP socket, a pipe, a tty , etc.). Does anyone have more info on what kind of errors <code>select</code> can report on the different kinds of descriptors?</p>