Updated: 2022/Sep/29

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BIND(2)                       System Calls Manual                      BIND(2)

     bind - bind a name to a socket

     Standard C Library (libc, -lc)

     #include <sys/socket.h>

     bind(int s, const struct sockaddr *name, socklen_t namelen);

     bind() assigns a name to an unnamed socket.  When a socket is created
     with socket(2) it exists in a name space (address family) but has no name
     assigned.  bind() requests that name be assigned to the socket.  namelen
     indicates the amount of space pointed to by name, in bytes.

     Binding a name in the UNIX domain creates a socket in the file system
     that must be deleted by the caller when it is no longer needed (using

     The rules used in name binding vary between communication domains.
     Consult the manual entries in section 4 for detailed information.

     If the bind is successful, a 0 value is returned.  A return value of -1
     indicates an error, which is further specified in the global errno.

     The bind() call will fail if:

     [EACCES]           The requested address is protected, and the current
                        user has inadequate permission to access it.

     [EADDRINUSE]       The specified address is already in use.

     [EADDRNOTAVAIL]    The specified address is not available from the local

     [EAFNOSUPPORT]     Addresses in the specified address family cannot be
                        used with this socket.

     [EBADF]            s is not a valid descriptor.

     [EFAULT]           The name parameter is not in a valid part of the user
                        address space.

     [EINVAL]           The socket is already bound to an address; or the
                        family of the socket and that requested in
                        name->sa_family are not equivalent.

     [EINVAL]           The socket address length passed was outside the
                        allowable range.

     [ENOTSOCK]         s is not a socket.

     The following errors are specific to binding names in the UNIX domain.

     [EIO]              An I/O error occurred while making the directory entry
                        or allocating the inode.

     [EISDIR]           An empty pathname was specified.

     [ELOOP]            Too many symbolic links were encountered in
                        translating the pathname.

     [ENAMETOOLONG]     A component of a pathname exceeded {NAME_MAX}
                        characters, or an entire path name exceeded {PATH_MAX}

     [ENOENT]           A prefix component of the path name does not exist.

     [ENOTDIR]          A component of the path prefix is not a directory.

     [EROFS]            The name would reside on a read-only file system.

     connect(2), getsockname(2), listen(2), socket(2), inet(4), inet6(4)

     The bind() function call appeared in 4.2BSD.

     bind() was changed in NetBSD 1.4 to prevent the binding of a socket to
     the same port as an existing socket when all of the following is true:
              either of the existing or new addresses is INADDR_ANY,
              the uid of the new socket is not root, and the uids of the
               creators of the sockets are different,
              the address is not a multicast address, and
              both sockets are not bound to INADDR_ANY with SO_REUSEPORT set.

     This prevents an attack where a user could bind to a port with the host's
     IP address (after setting SO_REUSEADDR) and `steal' packets destined for
     a server that bound to the same port with INADDR_ANY.

     bind() was changed in NetBSD 4.0 to honor the user's umask when binding
     sockets in the local domain.  This was done to match the behavior of
     other operating systems, including FreeBSD, OpenBSD, and Linux, and to
     improve compatibility with some third-party software.  Please note that
     this behavior is not portable.  If you must bind a local socket in a
     portable and secure way, you need to make a directory with tight
     permissions and then create the socket inside it.

NetBSD 10.99                     June 28, 2022                    NetBSD 10.99