1.\" $OpenBSD: unix.4,v 1.5 2000/12/21 21:01:21 aaron Exp $ 2.\" $NetBSD: unix.4,v 1.3 1994/11/30 16:22:43 jtc Exp $ 3.\" 4.\" Copyright (c) 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)unix.4 8.1 (Berkeley) 6/9/93 36.\" 37.Dd June 9, 1993 38.Dt UNIX 4 39.Os 40.Sh NAME 41.Nm unix 42.Nd UNIX-domain protocol family 43.Sh SYNOPSIS 44.Fd #include <sys/types.h> 45.Fd #include <sys/un.h> 46.Sh DESCRIPTION 47The 48.Tn UNIX Ns -domain 49protocol family is a collection of protocols 50that provides local (on-machine) interprocess 51communication through the normal 52.Xr socket 2 53mechanisms. 54The 55.Tn UNIX Ns -domain 56family supports the 57.Dv SOCK_STREAM 58and 59.Dv SOCK_DGRAM 60socket types and uses 61filesystem pathnames for addressing. 62.Sh ADDRESSING 63.Tn UNIX Ns -domain 64addresses are variable-length filesystem pathnames of 65at most 104 characters. 66The include file 67.Aq Pa sys/un.h 68defines this address: 69.Bd -literal -offset indent 70struct sockaddr_un { 71 u_char sun_len; 72 u_char sun_family; 73 char sun_path[104]; 74}; 75.Ed 76.Pp 77Binding a name to a 78.Tn UNIX Ns -domain 79socket with 80.Xr bind 2 81causes a socket file to be created in the filesystem. 82This file is 83.Em not 84removed when the socket is closed\(em\c 85.Xr unlink 2 86must be used to remove the file. 87.Pp 88The 89.Tn UNIX Ns -domain 90protocol family does not support broadcast addressing or any form 91of 92.Dq wildcard 93matching on incoming messages. 94All addresses are absolute- or relative-pathnames 95of other 96.Tn UNIX Ns -domain 97sockets. 98Normal filesystem access-control mechanisms are also 99applied when referencing pathnames; e.g., the destination 100of a 101.Xr connect 2 102or 103.Xr sendto 2 104must be writable. 105.Sh PROTOCOLS 106The 107.Tn UNIX Ns -domain 108protocol family is comprised of simple 109transport protocols that support the 110.Dv SOCK_STREAM 111and 112.Dv SOCK_DGRAM 113abstractions. 114.Dv SOCK_STREAM 115sockets also support the communication of 116.Ux 117file descriptors through the use of the 118.Ar msg_control 119field in the 120.Ar msg 121argument to 122.Xr sendmsg 2 123and 124.Xr recvmsg 2 . 125.Pp 126Any valid descriptor may be sent in a message. 127The file descriptor(s) to be passed are described using a 128.Ar struct cmsghdr 129that is defined in the include file 130.Aq Pa sys/socket.h . 131The type of the message is 132.Dv SCM_RIGHTS , 133and the data portion of the messages is an array of integers 134representing the file descriptors to be passed. 135The number of descriptors being passed is defined 136by the length field of the message; 137the length field is the sum of the size of the header 138plus the size of the array of file descriptors. 139.Pp 140The received descriptor is a 141.Em duplicate 142of the sender's descriptor, as if it were created with a call to 143.Xr dup 2 . 144Per-process descriptor flags, set with 145.Xr fcntl 2 , 146are 147.Em not 148passed to a receiver. 149Descriptors that are awaiting delivery, or that are 150purposely not received, are automatically closed by the system 151when the destination socket is closed. 152.Sh SEE ALSO 153.Xr socket 2 , 154.Xr netintro 4 155.Rs 156.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 157.%B PS1 158.%N 7 159.Re 160.Rs 161.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 162.%B PS1 163.%N 8 164.Re 165