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