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.\" $FreeBSD: src/share/man/man4/unix.4,v 1.3.2.4 2002/04/22 08:59:53 dd Exp $ 34.\" $DragonFly: src/share/man/man4/unix.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ 35.\" 36.Dd July 15, 2001 37.Dt UNIX 4 38.Os 39.Sh NAME 40.Nm unix 41.Nd UNIX-domain protocol family 42.Sh SYNOPSIS 43.In sys/types.h 44.In sys/un.h 45.Sh DESCRIPTION 46The 47.Ux 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.Ux 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.Ux 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.Ux 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 84.Xr unlink 2 85must be used to remove the file. 86.Pp 87The 88.Ux 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.Ux 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.Ux 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.Va msg_control 118field in the 119.Fa 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.Vt "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.Pp 152The effective credentials (i.e., the user ID and group list) of a 153peer on a 154.Dv SOCK_STREAM 155socket may be obtained using the 156.Dv LOCAL_PEERCRED 157socket option. 158This may be used by a server to obtain and verify the credentials of 159its client, and vice versa by the client to verify the credentials 160of the server. 161These will arrive in the form of a filled in 162.Vt "struct xucred" 163(defined in 164.Aq Pa sys/ucred.h ) . 165The credentials presented to the server (the 166.Xr listen 2 167caller) are those of the client when it called 168.Xr connect 2 ; 169the credentials presented to the client (the 170.Xr connect 2 171caller) are those of the server when it called 172.Xr listen 2 . 173This mechanism is reliable; there is no way for either party to influence 174the credentials presented to its peer except by calling the appropriate 175system call (e.g., 176.Xr connect 2 177or 178.Xr listen 2 ) 179under different effective credentials. 180.Sh SEE ALSO 181.Xr socket 2 , 182.Xr intro 4 183.Rs 184.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 185.%B PS1 186.%N 7 187.Re 188.Rs 189.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 190.%B PS1 191.%N 8 192.Re 193