man/man3c/dup2.3c

         te
 Copyright (c) 2013, OmniTI Computer Consulting, Inc. All rights reserved.
 Copyright (c) 2003, Sun Microsystems, Inc. All Rights Reserved.
 Copyright 1989 AT&T
 Copyright 2024 Oxide Computer Company
 The contents of this file are subject to the terms of the Common Development and Distribution License (the "License"). You may not use this file except in compliance with the License.
 You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing. See the License for the specific language governing permissions and limitations under the License.
 When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner]
 DUP2 3C "June 21, 2024"
 NAME
dup2, dup3 - duplicate an open file descriptor
 SYNOPSIS
#include <unistd.h>

int dup2(int fildes, int fildes2);


int dup3(int fildes, int fildes2, int flags);


 DESCRIPTION
The dup2() function causes the file descriptor fildes2 to refer to
the same file as fildes. The fildes argument is a file descriptor
referring to an open file, and fildes2 is a non-negative integer less
than the current value for the maximum number of open file descriptors allowed
the calling process. See getrlimit(2). If fildes2 already refers
to an open file, not fildes, it is closed first. If fildes2 refers
to fildes, or if fildes is not a valid open file descriptor,
fildes2 will not be closed first.

The dup2() function is equivalent to fcntl(fildes,
F_DUP2FD, fildes2). The returned file descriptor will have neither
the close-on-exec (FD_CLOEXEC) or close-on-fork (FD_CLOFORK) flags
set on it, regardless of what is set on fildes.

The dup3() function works similarly to the dup2() function with
two exceptions. If fildes and fildes2 point to the same file
descriptor, -1 is returned and errno set to EINVAL. The flags
argument allows for control of the returned file descriptor's flags. Valid
values are the bitwise-inclusive-OR of:

O_CLOEXEC

The returned file descriptor will have the close-on-exec flag, FD_CLOEXEC
set on it. The file descriptor will be automatically closed when the process
calls the exec(2) family of functions.


O_CLOFORK

The returned file descriptor will have the close-on-fork flag, FD_CLOFORK
set on it. The file descriptor will be automatically closed in any child
processes created with the fork(2) family of functions. It will remain
open in the parent.


 RETURN VALUES
Upon successful completion a non-negative integer representing the file
descriptor is returned. Otherwise, -1 is returned and errno is
set to indicate the error.
 ERRORS
The dup2() and dup3() functions will fail if:
EBADF

The fildes argument is not a valid open file descriptor.


EBADF

The fildes2 argument is negative or is not less than the current resource
limit returned by getrlimit(RLIMIT_NOFILE, .\|.\|.).


EINTR

A signal was caught during the dup2() call.


EMFILE

The process has too many open files. See fcntl(2).


Additionally, the dup3() function will fail if:
EINVAL

flags has a value other than 0 or the bitwise-inclusive-OR of
O_CLOEXEC and O_CLOFORK. fildes and fildes2 point to
the same file descriptor.


 ATTRIBUTES
See attributes(7) for descriptions of the following attributes:


ATTRIBUTE TYPE ATTRIBUTE VALUE
Interface Stability Standard
MT-Level Async-Signal-Safe


 SEE ALSO
 close (2),  creat (2),  exec (2),  fcntl (2),  fork (2),  getrlimit (2),  open (2),  pipe (2),  attributes (7),  standards (7)