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/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

       It is normally necessary to assign a local address using bind()
       before a SOCK_STREAM socket may receive connections (see

       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

       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         top

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

ERRORS         top

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

              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 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.

              The file descriptor sockfd does not refer to a socket.

       The following errors are specific to UNIX domain (AF_UNIX)

       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 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 4.2BSD).

NOTES         top

       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));
           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 5.13 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

Linux                          2021-03-22                        BIND(2)

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