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
          discussion 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) */
   }

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

   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at
   https://www.kernel.org/doc/man-pages/.

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