bind(2) System Calls Manual bind(2)
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 (ad-
dress family) but has no address assigned to it. bind() assigns the ad-
dress 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 ad-
dress 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");
}
SEE ALSO
accept(2), connect(2), getsockname(2), listen(2), socket(2), getad-
drinfo(3), getifaddrs(3), ip(7), ipv6(7), path_resolution(7), socket(7),
unix(7)
Linux man-pages 6.9.1 2024-06-15 bind(2)
Generated by dwww version 1.16 on Tue Dec 16 04:32:01 CET 2025.