Re: /dev/ttyX not-blocking

From: Theodore Y. Ts'o (tytso@MIT.EDU)
Date: Sat Jul 29 2000 - 22:15:16 EST


   Date: Sat, 29 Jul 2000 22:21:21 -0400 (EDT)
   From: Edward Muller <edwardam@home.com>

   I've written a small program that opens a /dev/ttySX device, in
   blocking mode (ie. O_RDONLY flag only), when the open call returns,
   it closes the device and runs another program. This way I know
   something was connected to the port and assuming the deivce is not
   removed the program called will work.

   But...I rebooted my machine today (running 2.2.14 from redhat) and
   the program no longer works...

   I've searched high and low and can't find an explanation...

If you want the /dev/ttySx device to block waiting for carier detect,
you need to make sure that the CLOCAL termios flag (see the stty man
page) is not set.

                                                        - Ted

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