BIND

Section: Linux Programmer's Manual (2)
Updated: 2004-06-23
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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);

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." 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];
}

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); 
    }
    ...
}

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EACCES: The address is protected, and the user is not the superuser.
EADDRINUSE: The given address is already in use.
EBADF: sockfd is not a valid descriptor.
EINVAL: The socket is already bound to an address.
ENOTSOCK: sockfd is a descriptor for a file, not 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(2).)
EADDRNOTAVAIL: A non-existent interface was requested or the requested address was not local.
EFAULT: my_addr points outside the user's accessible address space.
EINVAL: The addrlen is wrong, or the socket was not in the AF_UNIX family.
ELOOP: Too many symbolic links were encountered in resolving my_addr.
ENAMETOOLONG: my_addr is too long.
ENOENT: The file 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 file system.

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).