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BIND(2) Linux Programmer's Manual BIND(2)

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  discus-
            sion of /proc/sys/net/ipv4/ip_local_port_range ip(7).

     EBADF  sockfd is not a valid file 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 A component in the directory prefix of the socket pathname  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.

     For background on the socklen_t type, see 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) */ }