192 lines
5.5 KiB
Groff
192 lines
5.5 KiB
Groff
.\" Copyright (c) 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)unix.4 8.1 (Berkeley) 6/9/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd July 15, 2001
|
|
.Dt UNIX 4
|
|
.Os
|
|
.Sh NAME
|
|
.Nm unix
|
|
.Nd UNIX-domain protocol family
|
|
.Sh SYNOPSIS
|
|
.In sys/types.h
|
|
.In sys/un.h
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Ux Ns -domain
|
|
protocol family is a collection of protocols
|
|
that provides local (on-machine) interprocess
|
|
communication through the normal
|
|
.Xr socket 2
|
|
mechanisms.
|
|
The
|
|
.Ux Ns -domain
|
|
family supports the
|
|
.Dv SOCK_STREAM
|
|
and
|
|
.Dv SOCK_DGRAM
|
|
socket types and uses
|
|
file system pathnames for addressing.
|
|
.Sh ADDRESSING
|
|
.Ux Ns -domain
|
|
addresses are variable-length file system pathnames of
|
|
at most 104 characters.
|
|
The include file
|
|
.Aq Pa sys/un.h
|
|
defines this address:
|
|
.Bd -literal -offset indent
|
|
struct sockaddr_un {
|
|
u_char sun_len;
|
|
u_char sun_family;
|
|
char sun_path[104];
|
|
};
|
|
.Ed
|
|
.Pp
|
|
Binding a name to a
|
|
.Ux Ns -domain
|
|
socket with
|
|
.Xr bind 2
|
|
causes a socket file to be created in the file system.
|
|
This file is
|
|
.Em not
|
|
removed when the socket is closed \(em
|
|
.Xr unlink 2
|
|
must be used to remove the file.
|
|
.Pp
|
|
The
|
|
.Ux Ns -domain
|
|
protocol family does not support broadcast addressing or any form
|
|
of
|
|
.Dq wildcard
|
|
matching on incoming messages.
|
|
All addresses are absolute- or relative-pathnames
|
|
of other
|
|
.Ux Ns -domain
|
|
sockets.
|
|
Normal file system access-control mechanisms are also
|
|
applied when referencing pathnames; e.g., the destination
|
|
of a
|
|
.Xr connect 2
|
|
or
|
|
.Xr sendto 2
|
|
must be writable.
|
|
.Sh PROTOCOLS
|
|
The
|
|
.Ux Ns -domain
|
|
protocol family is comprised of simple
|
|
transport protocols that support the
|
|
.Dv SOCK_STREAM
|
|
and
|
|
.Dv SOCK_DGRAM
|
|
abstractions.
|
|
.Dv SOCK_STREAM
|
|
sockets also support the communication of
|
|
.Ux
|
|
file descriptors through the use of the
|
|
.Va msg_control
|
|
field in the
|
|
.Fa msg
|
|
argument to
|
|
.Xr sendmsg 2
|
|
and
|
|
.Xr recvmsg 2 .
|
|
.Pp
|
|
Any valid descriptor may be sent in a message.
|
|
The file descriptor(s) to be passed are described using a
|
|
.Vt "struct cmsghdr"
|
|
that is defined in the include file
|
|
.Aq Pa sys/socket.h .
|
|
The type of the message is
|
|
.Dv 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.
|
|
.Pp
|
|
The received descriptor is a
|
|
.Em duplicate
|
|
of the sender's descriptor, as if it were created with a call to
|
|
.Xr dup 2 .
|
|
Per-process descriptor flags, set with
|
|
.Xr fcntl 2 ,
|
|
are
|
|
.Em 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.
|
|
.Pp
|
|
The effective credentials (i.e., the user ID and group list) of a
|
|
peer on a
|
|
.Dv SOCK_STREAM
|
|
socket may be obtained using the
|
|
.Dv 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
|
|
.Vt "struct xucred"
|
|
(defined in
|
|
.Aq Pa sys/ucred.h ) .
|
|
The credentials presented to the server (the
|
|
.Xr listen 2
|
|
caller) are those of the client when it called
|
|
.Xr connect 2 ;
|
|
the credentials presented to the client (the
|
|
.Xr connect 2
|
|
caller) are those of the server when it called
|
|
.Xr 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.,
|
|
.Xr connect 2
|
|
or
|
|
.Xr listen 2 )
|
|
under different effective credentials.
|
|
.Sh SEE ALSO
|
|
.Xr socket 2 ,
|
|
.Xr intro 4
|
|
.Rs
|
|
.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
|
|
.%B PS1
|
|
.%N 7
|
|
.Re
|
|
.Rs
|
|
.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
|
|
.%B PS1
|
|
.%N 8
|
|
.Re
|