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.Dd May 26, 2002 26.Dt UUIDGEN 2 27.Os 28.Sh NAME 29.Nm uuidgen 30.Nd generate universally unique identifiers 31.Sh LIBRARY 32.Lb libc 33.Sh SYNOPSIS 34.In sys/uuid.h 35.Ft int 36.Fn uuidgen "struct uuid *store" "int count" 37.Sh DESCRIPTION 38The 39.Fn uuidgen 40system call generates 41.Fa count 42universally unique identifiers (UUIDs) and writes them to the buffer 43pointed to by 44.Fa store . 45The identifiers are generated according to the syntax and semantics of the 46DCE version 1 variant of universally unique identifiers. 47See below for a more in-depth description of the identifiers. 48When no IEEE 802 49address is available for the node field, a random multicast address is 50generated for each invocation of the system call. 51According to the algorithm of generating time-based UUIDs, this will also 52force a new random clock sequence, thereby increasing the likelihood for 53the identifier to be unique. 54.Pp 55When multiple identifiers are to be generated, the 56.Fn uuidgen 57system call will generate a set of identifiers that is dense in such a way 58that there is no identifier that is larger than the smallest identifier in the 59set and smaller than the largest identifier in the set and that is not already 60in the set. 61.Pp 62Universally unique identifiers, also known as globally unique identifiers 63(GUIDs), have a binary representation of 128-bits. 64The grouping and meaning of these bits is described by the following 65structure and its description of the fields that follow it: 66.Bd -literal 67struct uuid { 68 uint32_t time_low; 69 uint16_t time_mid; 70 uint16_t time_hi_and_version; 71 uint8_t clock_seq_hi_and_reserved; 72 uint8_t clock_seq_low; 73 uint8_t node[_UUID_NODE_LEN]; 74}; 75.Ed 76.Bl -tag -width ".Va clock_seq_hi_and_reserved" 77.It Va time_low 78The least significant 32 bits of a 60-bit timestamp. 79This field is stored in the native byte-order. 80.It Va time_mid 81The least significant 16 bits of the most significant 28 bits of the 60-bit 82timestamp. 83This field is stored in the native byte-order. 84.It Va time_hi_and_version 85The most significant 12 bits of the 60-bit timestamp multiplexed with a 4-bit 86version number. 87The version number is stored in the most significant 4 bits of the 16-bit 88field. 89This field is stored in the native byte-order. 90.It Va clock_seq_hi_and_reserved 91The most significant 6 bits of a 14-bit sequence number multiplexed with a 922-bit variant value. 93Note that the width of the variant value is determined by the variant itself. 94Identifiers generated by the 95.Fn uuidgen 96system call have variant value 10b. 97the variant value is stored in the most significant bits of the field. 98.It Va clock_seq_low 99The least significant 8 bits of a 14-bit sequence number. 100.It Va node 101The 6-byte IEEE 802 (MAC) address of one of the interfaces of the node. 102If no such interface exists, a random multi-cast address is used instead. 103.El 104.Pp 105The binary representation is sensitive to byte ordering. 106Any multi-byte field is to be stored in the local or native byte-order and 107identifiers must be converted when transmitted to hosts that do not agree 108on the byte-order. 109The specification does not however document what this means in concrete 110terms and is otherwise beyond the scope of this system call. 111.Sh RETURN VALUES 112.Rv -std 113.Sh ERRORS 114The 115.Fn uuidgen 116system call can fail with: 117.Bl -tag -width Er 118.It Bq Er EFAULT 119The buffer pointed to by 120.Fa store 121could not be written to for any or all identifiers. 122.It Bq Er EINVAL 123The 124.Fa count 125argument is less than 1 or larger than the hard upper limit of 2048. 126.El 127.Sh SEE ALSO 128.Xr uuidgen 1 , 129.Xr uuid 3 130.Sh STANDARDS 131The identifiers are represented and generated in conformance with the DCE 1.1 132RPC specification. 133The 134.Fn uuidgen 135system call is itself not part of the specification. 136.Sh HISTORY 137The 138.Fn uuidgen 139system call first appeared in 140.Fx 5.0 . 141