Linux manual pages Section 2: System Calls  

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 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: Macros and Conventions 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 filesystem.

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) */
}

SEE ALSO

accept(2), connect(2), getsockname(2), listen(2), socket(2), getaddrinfo(3), getifaddrs(3), ip(7), ipv6(7), path_resolution(7), socket(7), unix(7)

COLOPHON

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