Ubuntu Manpage: bind - bind a name to a socket

name
library
synopsis
description
return value
errors
standards
history
bugs
examples
see also

NAME

       bind - bind a name to a socket

LIBRARY

       Standard C library (libc, -lc)

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.

STANDARDS

       POSIX.1-2008.

HISTORY

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

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 <stdio.h>
       #include <stdlib.h>
       #include <string.h>
       #include <sys/socket.h>
       #include <sys/un.h>
       #include <unistd.h>

       #define MY_SOCK_PATH "/somepath"
       #define LISTEN_BACKLOG 50

       #define handle_error(msg) \
           do { perror(msg); exit(EXIT_FAILURE); } while (0)

       int
       main(void)
       {
           int                 sfd, cfd;
           socklen_t           peer_addr_size;
           struct sockaddr_un  my_addr, peer_addr;

           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)... */

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

           if (unlink(MY_SOCK_PATH) == -1)
               handle_error("unlink");
       }