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.\" $FreeBSD$ 26.\" 27.Dd May 26, 2002 28.Dt UUIDGEN 2 29.Os 30.Sh NAME 31.Nm uuidgen 32.Nd generate universally unique identifiers 33.Sh LIBRARY 34.Lb libc 35.Sh SYNOPSIS 36.In sys/uuid.h 37.Ft int 38.Fn uuidgen "struct uuid *store" "int count" 39.Sh DESCRIPTION 40The 41.Fn uuidgen 42system call generates 43.Fa count 44universally unique identifiers (UUIDs) and writes them to the buffer 45pointed to by 46.Fa store . 47The identifiers are generated according to the syntax and semantics of the 48DCE version 1 variant of universally unique identifiers. 49See below for a more in-depth description of the identifiers. 50When no IEEE 802 51address is available for the node field, a random multicast address is 52generated for each invocation of the system call. 53According to the algorithm of generating time-based UUIDs, this will also 54force a new random clock sequence, thereby increasing the likelihood for 55the identifier to be unique. 56.Pp 57When multiple identifiers are to be generated, the 58.Fn uuidgen 59system call will generate a set of identifiers that is dense in such a way 60that there is no identifier that is larger than the smallest identifier in the 61set and smaller than the largest identifier in the set and that is not already 62in the set. 63.Pp 64Universally unique identifiers, also known as globally unique identifiers 65(GUIDs), have a binary representation of 128-bits. 66The grouping and meaning of these bits is described by the following 67structure and its description of the fields that follow it: 68.Bd -literal 69struct uuid { 70 uint32_t time_low; 71 uint16_t time_mid; 72 uint16_t time_hi_and_version; 73 uint8_t clock_seq_hi_and_reserved; 74 uint8_t clock_seq_low; 75 uint8_t node[_UUID_NODE_LEN]; 76}; 77.Ed 78.Bl -tag -width ".Va clock_seq_hi_and_reserved" 79.It Va time_low 80The least significant 32 bits of a 60-bit timestamp. 81This field is stored in the native byte-order. 82.It Va time_mid 83The least significant 16 bits of the most significant 28 bits of the 60-bit 84timestamp. 85This field is stored in the native byte-order. 86.It Va time_hi_and_version 87The most significant 12 bits of the 60-bit timestamp multiplexed with a 4-bit 88version number. 89The version number is stored in the most significant 4 bits of the 16-bit 90field. 91This field is stored in the native byte-order. 92.It Va clock_seq_hi_and_reserved 93The most significant 6 bits of a 14-bit sequence number multiplexed with a 942-bit variant value. 95Note that the width of the variant value is determined by the variant itself. 96Identifiers generated by the 97.Fn uuidgen 98system call have variant value 10b. 99the variant value is stored in the most significant bits of the field. 100.It Va clock_seq_low 101The least significant 8 bits of a 14-bit sequence number. 102.It Va node 103The 6-byte IEEE 802 (MAC) address of one of the interfaces of the node. 104If no such interface exists, a random multi-cast address is used instead. 105.El 106.Pp 107The binary representation is sensitive to byte ordering. 108Any multi-byte field is to be stored in the local or native byte-order and 109identifiers must be converted when transmitted to hosts that do not agree 110on the byte-order. 111The specification does not however document what this means in concrete 112terms and is otherwise beyond the scope of this system call. 113.Sh RETURN VALUES 114.Rv -std 115.Sh ERRORS 116The 117.Fn uuidgen 118system call can fail with: 119.Bl -tag -width Er 120.It Bq Er EFAULT 121The buffer pointed to by 122.Fa store 123could not be written to for any or all identifiers. 124.It Bq Er EINVAL 125The 126.Fa count 127argument is less than 1 or larger than the hard upper limit of 2048. 128.El 129.Sh SEE ALSO 130.Xr uuidgen 1 , 131.Xr uuid 3 132.Sh STANDARDS 133The identifiers are represented and generated in conformance with the DCE 1.1 134RPC specification. 135The 136.Fn uuidgen 137system call is itself not part of the specification. 138.Sh HISTORY 139The 140.Fn uuidgen 141system call first appeared in 142.Fx 5.0 . 143