bind

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



NAME
       bind - bind a name to a socket

SYNOPSIS
       #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 EXAMPLES below.

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set
       to indicate the error.

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

           memset(&my_addr, 0, sizeof(my_addr));
           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 5.13 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/.



Linux                              2021-03-22                            BIND(2)