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