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Full Discussion: dup()
Top Forums Programming dup() Post 9588 by reddyb on Tuesday 30th of October 2001 12:40:00 PM
Old 10-30-2001
dup in unix
hi ..,

You are right, its used to duplicate the file discriptor.

the application demands the situation for example,

you have a client to pull data from a server on a different m/c and
you want your clients to run as daemon processes,
you can not associate any terminal device associated for daemon processes.
In this case, you open a null file discriptor with
open("/dev/null",O_RDONLY)
and dup this discriptor for stdin , stdout and stderr.
this prevents your processes from directly writing or reading from stdio.

I hope this might help you a bit in understanding.

thanks
reddyb
 

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LEARN ABOUT SUSE

tty

TTY(4)							     Linux Programmer's Manual							    TTY(4)

NAME

       tty - controlling terminal

DESCRIPTION

       The  file /dev/tty is a character file with major number 5 and minor number 0, usually of mode 0666 and owner.group root.tty.  It is a syn-
       onym for the controlling terminal of a process, if any.

       In addition to the ioctl(2) requests supported by the device that tty refers to, the ioctl(2) request TIOCNOTTY is supported.

   TIOCNOTTY
       Detach the calling process from its controlling terminal.

       If the process is the session leader, then SIGHUP and SIGCONT signals are sent to the foreground process group and  all	processes  in  the
       current session lose their controlling tty.

       This ioctl(2) call only works on file descriptors connected to /dev/tty.  It is used by daemon processes when they are invoked by a user at
       a terminal.  The process attempts to open /dev/tty.  If the open succeeds, it detaches itself from the terminal by using  TIOCNOTTY,  while
       if the open fails, it is obviously not attached to a terminal and does not need to detach itself.

FILES

       /dev/tty

SEE ALSO

       chown(1), mknod(1), ioctl(2), termios(3), console(4), tty_ioctl(4), ttyS(4), agetty(8), mingetty(8)

COLOPHON

       This  page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2003-04-07								    TTY(4)
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