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NAME    [Toc]    [Back]

     unix -- UNIX-domain protocol family

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     The UNIX-domain protocol family is a collection of protocols that provides
 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 file system pathnames for addressing.

ADDRESSING    [Toc]    [Back]

     UNIX-domain addresses are variable-length file system 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 file system.	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
     file system access-control mechanisms are also applied when referencing
     pathnames; e.g., the destination of a connect(2) or sendto(2) must be

PROTOCOLS    [Toc]    [Back]

     The UNIX-domain protocol family is comprised of simple transport protocols
 that support the SOCK_STREAM and SOCK_DGRAM abstractions.
     SOCK_STREAM sockets also support the communication of UNIX 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
     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 awaiting
 delivery, or that are purposely not received, are automatically
     closed by the system when the destination socket is closed.

     The effective credentials (i.e., the user ID and group list) of a peer on
     a SOCK_STREAM socket may be obtained using the LOCAL_PEERCRED socket
     option.  This may be used by a server to obtain and verify the credentials
 of its client, and vice versa by the client to verify the credentials
 of the server.  These will arrive in the form of a filled in struct
     xucred (defined in <sys/ucred.h>).  The credentials presented to the
     server (the listen(2) caller) are those of the client when it called
     connect(2); the credentials presented to the client (the connect(2)
     caller) are those of the server when it called listen(2).	This mechanism
     is reliable; there is no way for either party to influence the credentials
 presented to its peer except by calling the appropriate system call
     (e.g., connect(2) or listen(2)) under different effective credentials.

SEE ALSO    [Toc]    [Back]

     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 5.2.1			 July 15, 2001			 FreeBSD 5.2.1
[ Back ]
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