What can cause a “Resource temporarily unavailable” on sock send() command

Question

What can cause a Resource temporarily unavailable error on a socket send() command? The socket is setup as AF_UNIX, SOCK_STREAM. It wo

Answer 1

That's because you're using a non-blocking socket and the output buffer is full.

From the send() man page

   When the message does not fit into  the  send  buffer  of  the  socket,
   send() normally blocks, unless the socket has been placed in non-block-
   ing I/O mode.  In non-blocking mode it  would  return  EAGAIN  in  this
   case.  

EAGAIN is the error code tied to "Resource temporarily unavailable"

Consider using select() to get a better control of this behaviours