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UNIX(4)		       FreeBSD Kernel Interfaces Manual		       UNIX(4)

NAME
     unix -- UNIX-domain protocol family

SYNOPSIS
     #include <sys/types.h>
     #include <sys/un.h>

DESCRIPTION
     The UNIX-domain protocol family is	a collection of	protocols that pro-
     vides local (on-machine) interprocess communication through the normal
     socket(2) mechanisms.  The	UNIX-domain family supports the	SOCK_STREAM
     and SOCK_DGRAM socket types and uses filesystem pathnames for addressing.

ADDRESSING
     UNIX-domain addresses are variable-length filesystem pathnames of at most
     104 characters.  The include file <sys/un.h> defines this address:

	   struct sockaddr_un {
	   u_char  sun_len;
	   u_char  sun_family;
	   char	   sun_path[104];
	   };

     Binding a name to a UNIX-domain socket with bind(2) causes	a socket file
     to	be created in the filesystem.  This file is not	removed	when the
     socket is closed -- unlink(2) must	be used	to remove the file.

     The UNIX-domain protocol family does not support broadcast	addressing or
     any form of ``wildcard'' matching on incoming messages.  All addresses
     are absolute- or relative-pathnames of other UNIX-domain sockets.	Normal
     filesystem	access-control mechanisms are also applied when	referencing
     pathnames;	e.g., the destination of a connect(2) or sendto(2) must	be
     writable.

PROTOCOLS
     The UNIX-domain protocol family is	comprised of simple transport proto-
     cols that support the SOCK_STREAM and SOCK_DGRAM abstractions.
     SOCK_STREAM sockets also support the communication	of UNIX	file descrip-
     tors through the use of the msg_control field in the msg argument to
     sendmsg(2)	and recvmsg(2).

     Any valid descriptor may be sent in a message.  The file descriptor(s) to
     be	passed are described using a struct cmsghdr that is defined in the
     include file <sys/socket.h>.  The type of the message is SCM_RIGHTS, and
     the data portion of the messages is an array of integers representing the
     file descriptors to be passed.  The number	of descriptors being passed is
     defined by	the length field of the	message; the length field is the sum
     of	the size of the	header plus the	size of	the array of file descriptors.

     The received descriptor is	a duplicate of the sender's descriptor,	as if
     it	were created with a call to dup(2).  Per-process descriptor flags, set
     with fcntl(2), are	not passed to a	receiver.  Descriptors that are	await-
     ing delivery, or that are purposely not received, are automatically
     closed by the system when the destination socket is closed.

SEE ALSO
     socket(2),	intro(4)

     "An Introductory 4.3 BSD Interprocess Communication Tutorial", PS1, 7.

     "An Advanced 4.3 BSD Interprocess Communication Tutorial",	PS1, 8.

FreeBSD	9.3			 June 9, 1993			   FreeBSD 9.3

NAME | SYNOPSIS | DESCRIPTION | ADDRESSING | PROTOCOLS | SEE ALSO

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