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LOCALDOMAIN(4)		    BSD Programmer's Manual		LOCALDOMAIN(4)

NAME
     localdomain - LOCAL-domain protocol family

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

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

ADDRESSING
     LOCAL-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];
	   };

     sun_len	 The total length of the sockaddr, which includes the length
		 of the path string excluding the trailing null.

     sun_family	 The address family, AF_LOCAL.

     sun_path	 The path name of the socket end-point.	 A trailing null may
		 be included for convenience, but it should not be included in
		 the sun_len field.

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

     The LOCAL-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 LOCAL-domain sockets.	 Nor-
     mal filesystem access-control mechanisms are also applied when referenc-
     ing pathnames; e.g., the destination of a connect(2) or sendto(2) must be
     writable.

PROTOCOLS
     The LOCAL-domain protocol family is composed of simple transport proto-
     cols that support the SOCK_STREAM and SOCK_DGRAM abstractions.
     SOCK_STREAM sockets also support the communication of file descriptors
     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 in-
     clude 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
     awaiting delivery, or that are purposely not received, are automatically
     closed by the system when the destination socket is closed.

     The credentials of the sending process are also available via the control
     message interface.	 Credentials of a process consist of the its real and
     effective uid, groups and login name (as specified by setlogin(2))	 as
     provided in the struct fcred struct defined in <sys/ucred.h>. On a
     SOCK_DGRAM socket, the credentials are passed with every packet.  On a
     SOCK_STREAM socket, the credential are passed once, when the socket is
     first read.  Reception of credentials is controlled by using setsock-
     opt(2) to enable LOCAL_CRED at the SOL_SOCKET level.

SEE ALSO
     recv(2),  send(2),	 socket(2),  intro(4)

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

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

BSDI BSD/OS			 June 9, 1993				     2
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