bind(2) — Linux manual page


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

NAME         top

       bind - bind a name to a socket

SYNOPSIS         top

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

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

DESCRIPTION         top

       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 be‐

RETURN VALUE         top

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

ERRORS         top

       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 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

       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.

              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).)

              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.

              addr is too long.

       ENOENT A component in the directory prefix of the socket pathname
              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.

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (bind() first appeared in

NOTES         top

       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         top

       The transparent proxy options are not described.

EXAMPLES         top

       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)

       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(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)

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

           /* 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,
           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) */

SEE ALSO         top

       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         top

       This page is part of release 5.09 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

Linux                            2020-11-01                          BIND(2)

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