#### E.13.4 The `F` Reply Packet

The `F` reply packet has the following format:

``Fretcode,errno,Ctrl-C flag;call-specific attachment`'
  retcode is the return code of the system call as hexadecimal value.

  errno is the `errno` set by the call, in protocol-specific representation. This parameter can be omitted if the call was successful.

  Ctrl-C flag is only sent if the user requested a break. In this case, errno must be sent as well, even if the call was successful. The Ctrl-C flag itself consists of the character ``C`':

                F0,0,C

  or, if the call was interrupted before the host call has been performed:

                F-1,4,C

  assuming 4 is the protocol-specific representation of `EINTR`.