bind - bind a name to a socket
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
int bind(int sockfd, const struct sockaddr *addr,
socklen_t addrlen);
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 EXAMPLE below.
On success, zero is returned. On error, -1 is returned, and
errno is set
appropriately.
- 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.
POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (
bind() first appeared in
4.2BSD).
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).
The transparent proxy options are not described.
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)
int
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)
handle_error("socket");
memset(&my_addr, 0, sizeof(struct sockaddr_un));
/* 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(struct sockaddr_un)) == -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(struct sockaddr_un);
cfd = accept(sfd, (struct sockaddr *) &peer_addr,
&peer_addr_size);
if (cfd == -1)
handle_error("accept");
/* 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) */
}
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)