.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu) .\" and Copyright 2005-2007, Michael Kerrisk .\" Portions extracted from /usr/include/sys/socket.h, which does not have .\" any authorship information in it. It is probably available under the GPL. .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .\" .\" Other portions are from the 6.9 (Berkeley) 3/10/91 man page: .\" .\" Copyright (c) 1983 The Regents of the University of California. .\" All rights reserved. .\" .\" SPDX-License-Identifier: BSD-4-Clause-UC .\" .\" Modified Mon Oct 21 23:05:29 EDT 1996 by Eric S. Raymond .\" Modified 1998 by Andi Kleen .\" $Id: bind.2,v 1.3 1999/04/23 19:56:07 freitag Exp $ .\" Modified 2004-06-23 by Michael Kerrisk .\" .TH bind 2 2023-10-31 "Linux man-pages 6.7" .SH NAME bind \- bind a name to a socket .SH LIBRARY Standard C library .RI ( libc ", " \-lc ) .SH SYNOPSIS .nf .B #include .P .BI "int bind(int " sockfd ", const struct sockaddr *" addr , .BI " socklen_t " addrlen ); .fi .SH DESCRIPTION When a socket is created with .BR socket (2), it exists in a name space (address family) but has no address assigned to it. .BR bind () assigns the address specified by .I addr to the socket referred to by the file descriptor .IR sockfd . .I addrlen specifies the size, in bytes, of the address structure pointed to by .IR addr . Traditionally, this operation is called \[lq]assigning a name to a socket\[rq]. .P It is normally necessary to assign a local address using .BR bind () before a .B SOCK_STREAM socket may receive connections (see .BR accept (2)). .P The rules used in name binding vary between address families. Consult the manual entries in Section 7 for detailed information. For .BR AF_INET , see .BR ip (7); for .BR AF_INET6 , see .BR ipv6 (7); for .BR AF_UNIX , see .BR unix (7); for .BR AF_APPLETALK , see .BR ddp (7); for .BR AF_PACKET , see .BR packet (7); for .BR AF_X25 , see .BR x25 (7); and for .BR AF_NETLINK , see .BR netlink (7). .P The actual structure passed for the .I addr argument will depend on the address family. The .I sockaddr structure is defined as something like: .P .in +4n .EX struct sockaddr { sa_family_t sa_family; char sa_data[14]; } .EE .in .P The only purpose of this structure is to cast the structure pointer passed in .I addr in order to avoid compiler warnings. See EXAMPLES below. .SH RETURN VALUE On success, zero is returned. On error, \-1 is returned, and .I errno is set to indicate the error. .SH ERRORS .TP .B EACCES .\" e.g., privileged port in AF_INET domain The address is protected, and the user is not the superuser. .TP .B EADDRINUSE The given address is already in use. .TP .B 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 .I /proc/sys/net/ipv4/ip_local_port_range .BR ip (7). .TP .B EBADF .I sockfd is not a valid file descriptor. .TP .B EINVAL The socket is already bound to an address. .\" This may change in the future: see .\" .I linux/unix/sock.c for details. .TP .B EINVAL .I addrlen is wrong, or .I addr is not a valid address for this socket's domain. .TP .B ENOTSOCK The file descriptor .I sockfd does not refer to a socket. .P The following errors are specific to UNIX domain .RB ( AF_UNIX ) sockets: .TP .B EACCES Search permission is denied on a component of the path prefix. (See also .BR path_resolution (7).) .TP .B EADDRNOTAVAIL A nonexistent interface was requested or the requested address was not local. .TP .B EFAULT .I addr points outside the user's accessible address space. .TP .B ELOOP Too many symbolic links were encountered in resolving .IR addr . .TP .B ENAMETOOLONG .I addr is too long. .TP .B ENOENT A component in the directory prefix of the socket pathname does not exist. .TP .B ENOMEM Insufficient kernel memory was available. .TP .B ENOTDIR A component of the path prefix is not a directory. .TP .B EROFS The socket inode would reside on a read-only filesystem. .SH STANDARDS POSIX.1-2008. .SH HISTORY POSIX.1-2001, SVr4, 4.4BSD .RB ( bind () first appeared in 4.2BSD). .\" SVr4 documents an additional .\" .B ENOSR .\" general error condition, and .\" additional .\" .B EIO .\" and .\" .B EISDIR .\" UNIX-domain error conditions. .SH BUGS The transparent proxy options are not described. .\" FIXME Document transparent proxy options .SH EXAMPLES An example of the use of .BR bind () with Internet domain sockets can be found in .BR getaddrinfo (3). .P The following example shows how to bind a stream socket in the UNIX .RB ( AF_UNIX ) domain, and accept connections: .\" listen.7 refers to this example. .\" accept.7 refers to this example. .\" unix.7 refers to this example. .P .\" SRC BEGIN (bind.c) .EX #include #include #include #include #include #include \& #define MY_SOCK_PATH "/somepath" #define LISTEN_BACKLOG 50 \& #define handle_error(msg) \e 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"); } .EE .\" SRC END .SH SEE ALSO .BR accept (2), .BR connect (2), .BR getsockname (2), .BR listen (2), .BR socket (2), .BR getaddrinfo (3), .BR getifaddrs (3), .BR ip (7), .BR ipv6 (7), .BR path_resolution (7), .BR socket (7), .BR unix (7)