BIND(2)                   (2020-11-01)                    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 lqassigning a
          name to a socketrq.

          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 fami-
          lies.  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 EXAMPLES 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

     Page 1                        Linux             (printed 5/24/22)

     BIND(2)                   (2020-11-01)                    BIND(2)

               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 deter-
               mined 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 path-
               name does not exist.

     Page 2                        Linux             (printed 5/24/22)

     BIND(2)                   (2020-11-01)                    BIND(2)

          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 filesys-
               tem.

     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.

     EXAMPLES
          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);

     Page 3                        Linux             (printed 5/24/22)

     BIND(2)                   (2020-11-01)                    BIND(2)

              if (sfd == -1)
                  handle_error("socket");

              memset(&my_addr, 0, sizeof(my_addr));
                                  /* 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(my_addr)) == -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(peer_addr);
              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 5.10 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/.

     Page 4                        Linux             (printed 5/24/22)