dup2(2) 							System Calls Manual							   dup2(2)

NAME

       dup2 - duplicate an open file descriptor to a specific slot

SYNOPSIS

DESCRIPTION

       fildes is a file descriptor obtained from a or system call.

       fildes2 is a non-negative integer less than the maximum value allowed for file descriptors.

       causes fildes2 to refer to the same file as fildes.  If fildes2 refers to an already open file, the open file is closed first.

       The file descriptor returned by has the following in common with fildes:

	      o  Same open file (or pipe).

	      o  Same file pointer (that is, both file descriptors share one file pointer.)

	      o  Same access mode (read, write or read/write).

	      o  Same file status flags (see fcntl(2),

       The new file descriptor is set to remain open across system calls.  See fcntl(2).

       This  routine  is found in the C library.  Programs using but not using other routines from the Berkeley importability library (such as the
       routines described in bsdproc(3C)) should not give the option to ld(1).

RETURN VALUE

       Upon successful completion, returns the new file descriptor as a non-negative integer, fildes2.	Otherwise, it returns -1 and sets to indi-
       cate the error.

ERRORS

       fails if the following is true:

	      fildes	     is not a valid open file descriptor or fildes2 is not in the range of legal file descriptors.

	      An attempt to close
			     fildes2 was interrupted by a signal.  The file is still open.

WARNINGS

       A  multithreaded  application or an application with a signal handler can exhibit a race between on one thread and another kernel call that
       assigns a new file descriptor while running on a second thread or signal handler.  If fildes2 is free before the call was made,	the  other
       thread  or signal handler may win the race and acquire that descriptor (e.g., in an call).  The thread calling can then close this file and
       reuse the descriptor.  This results in multiple functions improperly referring to the same file.

       This race can be avoided either by ensuring that fildes2 references an open file before calling or by providing user-level  synchronization
       (or  signal  disabling) which makes sure that the thread and another thread or signal handler don't make competing calls into the kernel at
       the same time.

SEE ALSO

       close(2), creat(2), dup(2), exec(2), fcntl(2), open(2), pipe(2), privileges(5).

STANDARDS CONFORMANCE

																	   dup2(2)