1 .\" Copyright (c) 2002 Marcel Moolenaar
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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 $
33 .Nd generate universally unique identifiers
40 .Fn uuidgen "struct uuid *store" "int count"
46 universally unique identifiers (UUIDs) and writes them to the buffer
49 The identifiers are generated according to the syntax and semantics of the
50 DCE version 1 variant of universally unique identifiers.
51 See below for a more in-depth description of the identifiers.
53 address is available for the node field, a random multicast address is
54 generated for each invocation of the system call.
55 According to the algorithm of generating time-based UUIDs, this will also
56 force a new random clock sequence, thereby increasing the likelihood for
57 the identifier to be unique.
59 When multiple identifiers are to be generated, the
61 system call will generate a set of identifiers that is dense in such a way
62 that there is no identifier that is larger than the smallest identifier in the
63 set and smaller than the largest identifier in the set and that is not already
66 Universally unique identifiers, also known as globally unique identifiers
67 (GUIDs), have a binary representation of 128-bits.
68 The grouping and meaning of these bits is described by the following
69 structure and its description of the fields that follow it:
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];
80 .Bl -tag -width ".Va clock_seq_hi_and_reserved"
82 The least significant 32 bits of a 60-bit timestamp.
83 This field is stored in the native byte-order.
85 The least significant 16 bits of the most significant 28 bits of the 60-bit
87 This field is stored in the native byte-order.
88 .It Va time_hi_and_version
89 The most significant 12 bits of the 60-bit timestamp multiplexed with a 4-bit
91 The version number is stored in the most significant 4 bits of the 16-bit
93 This field is stored in the native byte-order.
94 .It Va clock_seq_hi_and_reserved
95 The most significant 6 bits of a 14-bit sequence number multiplexed with a
97 Note that the width of the variant value is determined by the variant itself.
98 Identifiers generated by the
100 system call have variant value 10b.
101 the variant value is stored in the most significant bits of the field.
103 The least significant 8 bits of a 14-bit sequence number.
105 The 6-byte IEEE 802 (MAC) address of one of the interfaces of the node.
106 If no such interface exists, a random multi-cast address is used instead.
109 The binary representation is sensitive to byte ordering.
110 Any multi-byte field is to be stored in the local or native byte-order and
111 identifiers must be converted when transmitted to hosts that do not agree
113 The specification does not however document what this means in concrete
114 terms and is otherwise beyond the scope of this system call.
120 system call can fail with:
123 The buffer pointed to by
125 could not be written to for any or all identifiers.
129 argument is less than 1 or larger than the hard upper limit of 2048.
135 The identifiers are represented and generated in conformance with the DCE 1.1
139 system call is itself not part of the specification.
143 system call first appeared in