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.\" Modified Mon Oct 21 23:05:29 EDT 1996 by Eric S. Raymond <esr@thyrsus.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.manpages@gmail.com>
.\"
.TH BIND 2 2007-12-28 "Linux" "Linux Programmer's Manual"
.SH NAME
bind \- bind a name to a socket
.SH SYNOPSIS
.nf
.BR "#include <sys/types.h>" "          /* See NOTES */"
.B #include <sys/socket.h>
.sp
.BI "int bind(int " sockfd ", const struct sockaddr *" addr ,
.BI "         socklen_t " addrlen );
.fi
.SH DESCRIPTION
When a socket is created with
.BR socket (2),
it exists in a name space (address family) but has no address assigned to it.
.BR bind ()
assigns the address specified to by
.I addr
to the socket referred to by the file descriptor
.IR sockfd .
.I addrlen
specifies the size, in bytes, of the address structure pointed to by
.IR addr .
Traditionally, this operation is called \(lqassigning a name to a socket\(rq.
.PP
It is normally necessary to assign a local address using
.BR bind ()
before a
.B SOCK_STREAM
socket may receive connections (see
.BR accept (2)).

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

The actual structure passed for the
.I addr
argument will depend on the address family.
The
.I sockaddr
structure is defined as something like:
.in +4n
.nf

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

.fi
.in
The only purpose of this structure is to cast the structure
pointer passed in
.I addr
in order to avoid compiler warnings.
See EXAMPLE below.
.SH "RETURN VALUE"
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EACCES
.\" e.g., privileged port in AF_INET domain
The address is protected, and the user is not the superuser.
.TP
.B EADDRINUSE
The given address is already in use.
.TP
.B EBADF
.I sockfd
is not a valid descriptor.
.TP
.B EINVAL
The socket is already bound to an address.
.\" This may change in the future: see
.\" .I linux/unix/sock.c for details.
.TP
.B ENOTSOCK
.I sockfd
is a descriptor for a file, not a socket.
.PP
The following errors are specific to Unix domain
.RB ( AF_UNIX )
sockets:
.TP
.B EACCES
Search permission is denied on a component of the path prefix.
(See also
.BR path_resolution (7).)
.TP
.B EADDRNOTAVAIL
A nonexistent interface was requested or the requested
address was not local.
.TP
.B EFAULT
.I addr
points outside the user's accessible address space.
.TP
.B EINVAL
The
.I addrlen
is wrong, or the socket was not in the
.B AF_UNIX
family.
.TP
.B ELOOP
Too many symbolic links were encountered in resolving
.IR addr .
.TP
.B ENAMETOOLONG
.I addr
is too long.
.TP
.B ENOENT
The file does not exist.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOTDIR
A component of the path prefix is not a directory.
.TP
.B EROFS
The socket inode would reside on a read-only file system.
.SH "CONFORMING TO"
SVr4, 4.4BSD, POSIX.1-2001
.RB ( bind ()
first appeared in 4.2BSD).
.\" SVr4 documents an additional
.\" .B ENOSR
.\" general error condition, and
.\" additional
.\" .B EIO
.\" and
.\" .B EISDIR
.\" Unix-domain error conditions.
.SH NOTES
POSIX.1-2001 does not require the inclusion of
.IR <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
.BR bind ()
is in reality an
.I int
(and this is what 4.x BSD and libc4 and libc5 have).
Some POSIX confusion resulted in the present
.IR socklen_t ,
also used by glibc.
See also
.BR accept (2).
.SH BUGS
The transparent proxy options are not described.
.\" FIXME What *are* transparent proxy options?
.SH EXAMPLE
An example of the use of
.BR bind ()
with Internet domain sockets can be found in
.BR getaddrinfo (3).

The following example shows how to bind a stream socket in the Unix
.RB ( AF_UNIX )
domain, and accept connections:
.\" listen.7 refers to this example.
.\" accept.7 refers to this example.
.\" unix.7 refers to this example.

.nf
#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) */
}
.fi
.SH "SEE ALSO"
.BR accept (2),
.BR connect (2),
.BR getsockname (2),
.BR listen (2),
.BR socket (2),
.BR getaddrinfo (3),
.BR getifaddrs (3),
.BR ip (7),
.BR ipv6 (7),
.BR path_resolution (7),
.BR socket (7),
.BR unix (7)
.SH COLOPHON
This page is part of release 3.27 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.