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DUP3(3) 		     Library Functions Manual			 DUP3(3)

NAME
     dup3 -- duplicate an existing file descriptor

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <fcntl.h>
     #include <unistd.h>

     int
     dup3(int oldd, int newd, int flags);

DESCRIPTION
     The dup3() function duplicates an existing object descriptor while allowing
     the value of the new descriptor to be specified.

     The  close-on-exec  flag  on  the	new file descriptor is determined by the
     O_CLOEXEC bit in flags.

     The close-on-fork flag on the new file  descriptor  is  determined  by  the
     O_CLOFORK bit in flags.

     The resolve-beneath flag on the new file descriptor is preserved.

     If  oldd  !=  newd  and flags == 0, the behavior is identical to dup2(oldd,
     newd).

     If oldd == newd, then dup3() fails, unlike dup2(2).

RETURN VALUES
     The value -1 is returned if an error occurs.  The external  variable  errno
     indicates the cause of the error.

ERRORS
     The dup3() function fails if:

     [EBADF]		The  oldd  argument  is not a valid active descriptor or
			the newd argument is negative or exceeds the maximum al-
			lowable descriptor number

     [EINVAL]		The oldd argument is equal to the newd argument.

     [EINVAL]		The flags argument has bits set other than O_CLOEXEC  or
			O_CLOFORK.

SEE ALSO
     accept(2), close(2), dup2(2), fcntl(2), getdtablesize(2), open(2), pipe(2),
     socket(2), socketpair(2)

STANDARDS
     The dup3() function does not conform to any standard.

HISTORY
     The  dup3() function appeared in FreeBSD 10.0.  The O_CLOFORK flag appeared
     in FreeBSD 15.0.

FreeBSD ports 15.quarterly	  May 17, 2025				 DUP3(3)

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<https://man.freebsd.org/cgi/man.cgi?query=dup3&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>

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