bind(2) — Linux manual pages

bind
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Name

bind — bind a name to a socket

Synopsis

#include <sys/types.h>           /* See NOTES */
#include <sys/socket.h>

`int bind(`	int	`sockfd`,
	const struct sockaddr *	`addr`,
	socklen_t	`addrlen)`;

DESCRIPTION

When a socket is created with socket(2), it exists in a name space (address family) but has no address assigned to it. bind() assigns the address specified to by addr to the socket referred to by the file descriptor sockfd. addrlen specifies the size, in bytes, of the address structure pointed to by addr. Traditionally, this operation is called “assigning a name to a socket”.

It is normally necessary to assign a local address using bind() before a SOCK_STREAM socket may receive connections (see accept(2)).

The rules used in name binding vary between address families. Consult the manual entries in Section 7 for detailed information. For AF_INET see ip(7), for AF_INET6 see ipv6(7), for AF_UNIX see unix(7), for AF_APPLETALK see ddp(7), for AF_PACKET see packet(7), for AF_X25 see x25(7) and for AF_NETLINK see netlink(7).

The actual structure passed for the addr argument will depend on the address family. The sockaddr structure is defined as something like:

struct sockaddr {

sa_family_t sa_family;

char sa_data[14];

};

The only purpose of this structure is to cast the structure pointer passed in addr in order to avoid compiler warnings. See EXAMPLE below.

RETURN VALUE

On success, zero is returned. On error, −1 is returned, and errno is set appropriately.

ERRORS

EACCES: The address is protected, and the user is not the superuser.
EADDRINUSE: The given address is already in use.
EBADF: sockfd is not a valid descriptor.
EINVAL: The socket is already bound to an address.
ENOTSOCK: sockfd is a descriptor for a file, not a socket.

The following errors are specific to UNIX domain (AF_UNIX) sockets:

EACCES: Search permission is denied on a component of the path prefix. (See also path_resolution(7).)
EADDRNOTAVAIL: A nonexistent interface was requested or the requested address was not local.
EFAULT: addr points outside the user's accessible address space.
EINVAL: The addrlen is wrong, or the socket was not in the AF_UNIX family.
ELOOP: Too many symbolic links were encountered in resolving addr.
ENAMETOOLONG: addr is too long.
ENOENT: The file does not exist.
ENOMEM: Insufficient kernel memory was available.
ENOTDIR: A component of the path prefix is not a directory.
EROFS: The socket inode would reside on a read-only file system.

CONFORMING TO

SVr4, 4.4BSD, POSIX.1-2001 (bind() first appeared in 4.2BSD).

NOTES

POSIX.1-2001 does not require the inclusion of <sys/types.h> and this header file is not required on Linux. However, some historical (BSD) implementations required this header file, and portable applications are probably wise to include it.

The third argument of bind() is in reality an int (and this is what 4.x BSD and libc4 and libc5 have). Some POSIX confusion resulted in the present socklen_t, also used by glibc. See also accept(2).

BUGS

The transparent proxy options are not described.

EXAMPLE

An example of the use of bind() with Internet domain sockets can be found in getaddrinfo(3).

The following example shows how to bind a stream socket in the Unix (AF_UNIX) domain, and accept connections:

#include <sys/socket.h>
#include <sys/un.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define MY_SOCK_PATH "/somepath"
#define LISTEN_BACKLOG 50

#define handle_error(msg) \
    do { perror(msg); exit(EXIT_FAILURE); } while (0)

int
main(int argc, char *argv[])
{
    int sfd, cfd;
    struct sockaddr_un my_addr, peer_addr;
    socklen_t peer_addr_size;

    sfd = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sfd == −1)
        handle_error("socket");

    memset(&my_addr, 0, sizeof(struct sockaddr_un));
                        /* Clear structure */
    my_addr.sun_family = AF_UNIX;
    strncpy(my_addr.sun_path, MY_SOCK_PATH,
            sizeof(my_addr.sun_path) − 1);

    if (bind(sfd, (struct sockaddr *) &my_addr,
            sizeof(struct sockaddr_un)) == −1)
        handle_error("bind");

    if (listen(sfd, LISTEN_BACKLOG) == −1)
        handle_error("listen");

    /* Now we can accept incoming connections one
       at a time using accept(2) */

    peer_addr_size = sizeof(struct sockaddr_un);
    cfd = accept(sfd, (struct sockaddr *) &peer_addr,
                 &peer_addr_size);
    if (cfd == −1)
        handle_error("accept");

    /* Code to deal with incoming connection(s)... */

    /* When no longer required, the socket pathname, MY_SOCK_PATH
       should be deleted using unlink(2) or remove(3) */
}

COLOPHON

This page is part of release 2.79 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/.

Copyright 1993 Rickard E. Faith (faithcs.unc.edu)
Portions extracted from /usr/include/sys/socket.h, which does not have
any authorship information in it.  It is probably available under the GPL.

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.

Other portions are from the 6.9 (Berkeley) 3/10/91 man page:

Copyright (c) 1983 The Regents of the University of California.
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.
3. All advertising materials mentioning features or use of this software
   must display the following acknowledgement:
    This product includes software developed by the University of
    California, Berkeley and its contributors.
4. Neither the name of the University nor the names of its contributors
   may be used to endorse or promote products derived from this software
   without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.

Modified Mon Oct 21 23:05:29 EDT 1996 by Eric S. Raymond <esrthyrsus.com>
Modified 1998 by Andi Kleen
$Id: bind.2,v 1.3 1999/04/23 19:56:07 freitag Exp $
Modified 2004-06-23 by Michael Kerrisk <mtk.manpagesgmail.com>

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struct	sockaddr {
	sa_family_t	`sa_family`;
	char	`sa_data`[14];
};