1.\" $NetBSD: uuidgen.2,v 1.4 2005/01/30 18:13:04 jwise Exp $ 2.\" $FreeBSD: src/lib/libc/sys/uuidgen.2,v 1.7 2003/06/27 13:41:29 yar Exp $ 3.\" Copyright (c) 2002 Marcel Moolenaar 4.\" 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.\" 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.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 17.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26.\" 27.\" $FreeBSD: src/lib/libc/sys/uuidgen.2,v 1.7 2003/06/27 13:41:29 yar Exp $ 28.\" 29.Dd May 26, 2002 30.Dt UUIDGEN 2 31.Os 32.Sh NAME 33.Nm uuidgen 34.Nd generate universally unique identifiers 35.Sh LIBRARY 36.Lb libc 37.Sh SYNOPSIS 38.In sys/types.h 39.In sys/uuid.h 40.Ft int 41.Fn uuidgen "struct uuid *store" "int count" 42.Sh DESCRIPTION 43The 44.Fn uuidgen 45system call generates 46.Fa count 47universally unique identifiers (UUIDs) and writes them to the buffer 48pointed to by 49.Fa store . 50The identifiers are generated according to the syntax and semantics of the 51DCE version 1 variant of universally unique identifiers. 52See below for a more in-depth description of the identifiers. 53When no IEEE 802 54address is available for the node field, a random multi-cast address is 55generated for each invocation of the system call. 56According to the algorithm of generating time-based UUIDs, this will also 57force a new random clock sequence, thereby increasing the likelihood for 58the identifier to be unique. 59.Pp 60When multiple identifiers are to be generated, the 61.Fn uuidgen 62system call will generate a set of identifiers that is dense in such a way 63that there is no identifier that is larger than the smallest identifier in the 64set and smaller than the largest identifier in the set and that is not already 65in the set. 66.Pp 67Universally unique identifiers, also known as globally unique identifiers 68(GUIDs), have a binary representation of 128-bits. 69The grouping and meaning of these bits is described by the following 70structure and its description of the fields that follow it: 71.Bd -literal 72struct uuid { 73 uint32_t time_low; 74 uint16_t time_mid; 75 uint16_t time_hi_and_version; 76 uint8_t clock_seq_hi_and_reserved; 77 uint8_t clock_seq_low; 78 uint8_t node[_UUID_NODE_LEN]; 79}; 80.Ed 81.Bl -tag -width ".Va clock_seq_hi_and_reserved" 82.It Va time_low 83The least significant 32 bits of a 60-bit timestamp. 84This field is stored in the native byte-order. 85.It Va time_mid 86The least significant 16 bits of the most significant 28 bits of the 60-bit 87timestamp. 88This field is stored in the native byte-order. 89.It Va time_hi_and_version 90The most significant 12 bits of the 60-bit timestamp multiplexed with a 4-bit 91version number. 92The version number is stored in the most significant 4 bits of the 16-bit 93field. 94This field is stored in the native byte-order. 95.It Va clock_seq_hi_and_reserved 96The most significant 6 bits of a 14-bit sequence number multiplexed with a 972-bit variant value. 98Note that the width of the variant value is determined by the variant itself. 99Identifiers generated by the 100.Fn uuidgen 101system call have variant value 10b. 102the variant value is stored in the most significant bits of the field. 103.It Va clock_seq_low 104The least significant 8 bits of a 14-bit sequence number. 105.It Va node 106The 6-byte IEEE 802 (MAC) address of one of the interfaces of the node. 107If no such interface exists, a random multi-cast address is used instead. 108.El 109.Pp 110The binary representation is sensitive to byte ordering. 111Any multi-byte field is to be stored in the local or native byte-order and 112identifiers must be converted when transmitted to hosts that do not agree 113on the byte-order. 114The specification does not however document what this means in concrete 115terms and is otherwise beyond the scope of this system call. 116.Sh RETURN VALUES 117.Rv -std 118.Sh ERRORS 119The 120.Fn uuidgen 121system call can fail with: 122.Bl -tag -width Er 123.It Bq Er EFAULT 124The buffer pointed to by 125.Fa store 126could not be written to for any or all identifiers. 127.It Bq Er EINVAL 128The 129.Fa count 130argument is less than 1 or larger than the hard upper limit of 2048. 131.El 132.Sh SEE ALSO 133.Xr uuidgen 1 , 134.Xr uuid 3 135.Sh STANDARDS 136The identifiers are represented and generated in conformance with the DCE 1.1 137RPC specification. 138The 139.Fn uuidgen 140system call is itself not part of the specification. 141.Sh HISTORY 142The 143.Fn uuidgen 144system call first appeared in 145.Fx 5.0 146and was subsequently added to 147.Nx 2.0 . 148