DUP3(3)

NAME
dup3 - duplicate an existing file descriptor

LIBRARY
libc

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.

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 allowable 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 and DragonFly 5.5.

The O_CLOFORK flag appeared in FreeBSD 15.0 and DragonFly 6.5.