bind() - Unix, Linux System Call
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NAME
bind - bind a name to a socket
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int bind(int sockfd, const struct sockaddr *my_addr ", socklen_t " addrlen );
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DESCRIPTION
bind() gives the socket sockfd the local address my_addr. my_addr is addrlen bytes long. Traditionally, this is called assigning a name to a socket.\(rq
When a socket is created with socket(2), it exists in a name space (address family) but has no name assigned.
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 my_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];
}
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The only purpose of this structure is to cast the structure pointer passed in
my_addr in order to avoid compiler warnings. The following example shows how this is done when binding a socket
in the Unix (AF_UNIX) domain:
#include <sys/socket.h>
#include <sys/un.h>
#include <stdlib.h>
#include <stdlio.h>
#define MY_SOCK_PATH "/somepath"
int
main(int argc, char *argv[])
{
int sfd;
struct sockaddr_un addr;
sfd = socket(AF_UNIX, SOCK_STREAM, 0);
if (sfd == -1) {
perror("socket");
exit(EXIT_FAILURE);
}
memset(&addr, 0, sizeof(struct sockaddr_un));
/* Clear structure */
addr.sun_family = AF_UNIX;
strncpy(addr.sun_path, MY_SOCK_PATH,
sizeof(addr.sun_path) - 1);
if (bind(sfd, (struct sockaddr *) &addr,
sizeof(struct sockaddr_un)) == -1) {
perror("bind");
exit(EXIT_FAILURE);
}
...
}
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RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
Error Code | Description |
EACCES |
The address is protected, and the user is not the superuser.
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EADDRINUSE |
The given address is already in use.
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EBADF |
sockfd is not a valid descriptor.
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EINVAL |
The socket is already bound to an address.
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ENOTSOCK |
sockfd is a descriptor for a file, not a socket.
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The following errors are specific to UNIX domain
(AF_UNIX) sockets:
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EACCES |
Search permission is denied on a component of the path prefix.
(See also
path_resolution(2).)
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EADDRNOTAVAIL |
A non-existent interface was requested or the requested
address was not local.
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EFAULT |
my_addr points outside the users accessible address space.
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EINVAL |
The
addrlen is wrong, or the socket was not in the
AF_UNIX family.
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ELOOP |
Too many symbolic links were encountered in resolving
my_addr. |
ENAMETOOLONG |
my_addr is too long.
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ENOENT |
The file does not exist.
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ENOMEM |
Insufficient kernel memory was available.
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ENOTDIR |
A component of the path prefix is not a directory.
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EROFS |
The socket inode would reside on a read-only file system.
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BUGS
The transparent proxy options are not described.
CONFORMING TO
SVr4, 4.4BSD (the bind() function first appeared in 4.2BSD).
NOTE
The third argument of
bind() is in reality an
int (and this is what 4.x BSD and libc4 and libc5 have).
Some POSIX confusion resulted in the present
socklen_t, also used by glibc.
See also
accept(2).
SEE ALSO
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