1.\" Copyright (c) 2002 Marcel Moolenaar 2.\" 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.\" 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24.\" 25.\" $FreeBSD: src/lib/libc/sys/uuidgen.2,v 1.8 2005/07/31 03:30:44 keramida Exp $ 26.\" $DragonFly: src/lib/libc/sys/uuidgen.2,v 1.1 2007/06/16 19:57:13 dillon Exp $ 27.\" 28.Dd May 26, 2002 29.Dt UUIDGEN 2 30.Os 31.Sh NAME 32.Nm uuidgen 33.Nd generate universally unique identifiers 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In sys/types.h 38.In sys/uuid.h 39.Ft int 40.Fn uuidgen "struct uuid *store" "int count" 41.Sh DESCRIPTION 42The 43.Fn uuidgen 44system call generates 45.Fa count 46universally unique identifiers (UUIDs) and writes them to the buffer 47pointed to by 48.Fa store . 49The identifiers are generated according to the syntax and semantics of the 50DCE version 1 variant of universally unique identifiers. 51See below for a more in-depth description of the identifiers. 52When no IEEE 802 53address is available for the node field, a random multicast address is 54generated for each invocation of the system call. 55According to the algorithm of generating time-based UUIDs, this will also 56force a new random clock sequence, thereby increasing the likelihood for 57the identifier to be unique. 58.Pp 59When multiple identifiers are to be generated, the 60.Fn uuidgen 61system call will generate a set of identifiers that is dense in such a way 62that there is no identifier that is larger than the smallest identifier in the 63set and smaller than the largest identifier in the set and that is not already 64in the set. 65.Pp 66Universally unique identifiers, also known as globally unique identifiers 67(GUIDs), have a binary representation of 128-bits. 68The grouping and meaning of these bits is described by the following 69structure and its description of the fields that follow it: 70.Bd -literal 71struct uuid { 72 uint32_t time_low; 73 uint16_t time_mid; 74 uint16_t time_hi_and_version; 75 uint8_t clock_seq_hi_and_reserved; 76 uint8_t clock_seq_low; 77 uint8_t node[_UUID_NODE_LEN]; 78}; 79.Ed 80.Bl -tag -width ".Va clock_seq_hi_and_reserved" 81.It Va time_low 82The least significant 32 bits of a 60-bit timestamp. 83This field is stored in the native byte-order. 84.It Va time_mid 85The least significant 16 bits of the most significant 28 bits of the 60-bit 86timestamp. 87This field is stored in the native byte-order. 88.It Va time_hi_and_version 89The most significant 12 bits of the 60-bit timestamp multiplexed with a 4-bit 90version number. 91The version number is stored in the most significant 4 bits of the 16-bit 92field. 93This field is stored in the native byte-order. 94.It Va clock_seq_hi_and_reserved 95The most significant 6 bits of a 14-bit sequence number multiplexed with a 962-bit variant value. 97Note that the width of the variant value is determined by the variant itself. 98Identifiers generated by the 99.Fn uuidgen 100system call have variant value 10b. 101the variant value is stored in the most significant bits of the field. 102.It Va clock_seq_low 103The least significant 8 bits of a 14-bit sequence number. 104.It Va node 105The 6-byte IEEE 802 (MAC) address of one of the interfaces of the node. 106If no such interface exists, a random multi-cast address is used instead. 107.El 108.Pp 109The binary representation is sensitive to byte ordering. 110Any multi-byte field is to be stored in the local or native byte-order and 111identifiers must be converted when transmitted to hosts that do not agree 112on the byte-order. 113The specification does not however document what this means in concrete 114terms and is otherwise beyond the scope of this system call. 115.Sh RETURN VALUES 116.Rv -std 117.Sh ERRORS 118The 119.Fn uuidgen 120system call can fail with: 121.Bl -tag -width Er 122.It Bq Er EFAULT 123The buffer pointed to by 124.Fa store 125could not be written to for any or all identifiers. 126.It Bq Er EINVAL 127The 128.Fa count 129argument is less than 1 or larger than the hard upper limit of 2048. 130.El 131.Sh SEE ALSO 132.Xr uuidgen 1 , 133.Xr uuid 3 134.Sh STANDARDS 135The identifiers are represented and generated in conformance with the DCE 1.1 136RPC specification. 137The 138.Fn uuidgen 139system call is itself not part of the specification. 140.Sh HISTORY 141The 142.Fn uuidgen 143system call first appeared in 144.Fx 5.0 . 145