man-pages/man2/bind.2

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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@gmx.net>
.\"
.TH BIND 2 2004-06-23 "Linux 2.6.7" "Linux Programmer's Manual"
.SH NAME
bind \- bind a name to a socket
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/socket.h>
.sp
.BI "int bind(int " sockfd ", const struct sockaddr *" my_addr \
", socklen_t " addrlen );
.fi
.SH DESCRIPTION
.BR bind ()
gives the socket
.I sockfd
the local address
.IR my_addr .
.I my_addr
is
.I addrlen
bytes long.
Traditionally, this is called \(lqassigning a name to a socket.\(rq
When a socket is created with
.BR socket (2),
it exists in a name space (address family) but has no name assigned.
.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 my_addr
argument will depend on the address family.
The
.I sockaddr
structure is defined as something like:
.in +0.25in
.nf

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

.fi
.in -0.25in
The only purpose of this structure is to cast the structure
pointer passed in
.I my_addr
in order to avoid compiler warnings.
The following example shows how this is done when binding a socket
in the Unix
.RB ( AF_UNIX )
domain:

.in +0.25in
.nf
#include <sys/socket.h>
#include <sys/un.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define MY_SOCK_PATH "/somepath"

int
main(int argc, char *argv[])
{
    int sfd;
    struct sockaddr_un addr;

    sfd = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sfd == -1) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

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

    if (bind(sfd, (struct sockaddr *) &addr,
            sizeof(struct sockaddr_un)) == -1) {
        perror("bind");
        exit(EXIT_FAILURE);
    }
    ...
}
.fi
.in -0.25in
.SH "RETURN VALUE"
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EACCES
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 (2).)
.TP
.B EADDRNOTAVAIL
A non-existent interface was requested or the requested
address was not local.
.TP
.B EFAULT
.I my_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 my_addr .
.TP
.B ENAMETOOLONG
.I my_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 BUGS
The transparent proxy options are not described.
.SH "CONFORMING TO"
SVr4, 4.4BSD, POSIX.1-2001 (the
.BR bind ()
function 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 NOTE
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 "SEE ALSO"
.BR accept (2),
.BR connect (2),
.BR getsockname (2),
.BR listen (2),
.BR path_resolution (2),
.BR socket (2),
.BR getaddrinfo (3),
.BR ip (7),
.BR ipv6 (7),
.BR socket (7),
.BR unix (7)