Ах да, мега чистильщик сообщений. Вот пруфы ЗА ТЕБЯ я дам. Как обычно. Ты же с ЛОРа, там пруфы не дают:

http://man7.org/linux/man-pages/man7/socket.7.html
       SO_LINGER
              Sets or gets the SO_LINGER option.  The argument is a linger
              structure.

                  struct linger {
                      int l_onoff;    /* linger active */
                      int l_linger;   /* how many seconds to linger for */
                  };

              When enabled, a close(2) or shutdown(2) will not return until
              all queued messages for the socket have been successfully sent
              or the linger timeout has been reached.  Otherwise, the call
              returns immediately and the closing is done in the background.
              When the socket is closed as part of exit(2), it always
              lingers in the background.