Ubuntu Manpage: bind - bind a name to a socket

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 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.

EADDRINUSE
(Internet domain sockets) The port number was specified as zero in the socket
address structure, but, upon attempting to bind to an ephemeral port, it was
determined that all port numbers in the ephemeral port range are currently in use.
See the discussion of /proc/sys/net/ipv4/ip_local_port_range ip(7).

EBADF sockfd is not a valid descriptor.

EINVAL The socket is already bound to an address.

EINVAL addrlen is wrong, or addr is not a valid address for this socket's domain.

ENOTSOCK
The file descriptor sockfd does not refer to 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.

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

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (bind() first appeared in 4.2BSD).

NOTES

       POSIX.1  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

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