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

       bind - bind a name to a socket

       #include <sys/types.h>          /* See NOTES */
       #include <sys/socket.h>

       int bind(int sockfd, const struct sockaddr *addr,
                socklen_t addrlen);

       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.

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

       EACCES The address is protected, and the user is not the superuser.

              The given address is already in use.

              (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 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.

              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

              A  nonexistent  interface  was  requested  or  the requested address was not

       EFAULT addr points outside the user's accessible address space.

       ELOOP  Too many symbolic links were encountered in resolving addr.

              addr is too long.

       ENOENT The file does not exist.

       ENOMEM Insufficient kernel memory was available.

              A component of the path prefix is not a directory.

       EROFS  The socket inode would reside on a read-only filesystem.

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

       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).

       The transparent proxy options are not described.

       An example of the use of bind() with Internet domain sockets can be found in getad‐

       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)

       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)

           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)

           if (listen(sfd, LISTEN_BACKLOG) == -1)

           /* 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,
           if (cfd == -1)

           /* 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) */

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

       This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.

Linux                                       2014-08-19                                    BIND(2)

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