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
39 .Fn uuidgen "struct uuid *store" "int count"
45 universally unique identifiers (UUIDs) and writes them to the buffer
48 The identifiers are generated according to the syntax and semantics of the
49 DCE version 1 variant of universally unique identifiers.
50 See below for a more in-depth description of the identifiers.
52 address is available for the node field, a random multicast address is
53 generated for each invocation of the system call.
54 According to the algorithm of generating time-based UUIDs, this will also
55 force a new random clock sequence, thereby increasing the likelihood for
56 the identifier to be unique.
58 When multiple identifiers are to be generated, the
60 system call will generate a set of identifiers that is dense in such a way
61 that there is no identifier that is larger than the smallest identifier in the
62 set and smaller than the largest identifier in the set and that is not already
65 Universally unique identifiers, also known as globally unique identifiers
66 (GUIDs), have a binary representation of 128-bits.
67 The grouping and meaning of these bits is described by the following
68 structure and its description of the fields that follow it:
73 uint16_t time_hi_and_version;
74 uint8_t clock_seq_hi_and_reserved;
75 uint8_t clock_seq_low;
76 uint8_t node[_UUID_NODE_LEN];
79 .Bl -tag -width ".Va clock_seq_hi_and_reserved"
81 The least significant 32 bits of a 60-bit timestamp.
82 This field is stored in the native byte-order.
84 The least significant 16 bits of the most significant 28 bits of the 60-bit
86 This field is stored in the native byte-order.
87 .It Va time_hi_and_version
88 The most significant 12 bits of the 60-bit timestamp multiplexed with a 4-bit
90 The version number is stored in the most significant 4 bits of the 16-bit
92 This field is stored in the native byte-order.
93 .It Va clock_seq_hi_and_reserved
94 The most significant 6 bits of a 14-bit sequence number multiplexed with a
96 Note that the width of the variant value is determined by the variant itself.
97 Identifiers generated by the
99 system call have variant value 10b.
100 the variant value is stored in the most significant bits of the field.
102 The least significant 8 bits of a 14-bit sequence number.
104 The 6-byte IEEE 802 (MAC) address of one of the interfaces of the node.
105 If no such interface exists, a random multi-cast address is used instead.
108 The binary representation is sensitive to byte ordering.
109 Any multi-byte field is to be stored in the local or native byte-order and
110 identifiers must be converted when transmitted to hosts that do not agree
112 The specification does not however document what this means in concrete
113 terms and is otherwise beyond the scope of this system call.
119 system call can fail with:
122 The buffer pointed to by
124 could not be written to for any or all identifiers.
128 argument is less than 1 or larger than the hard upper limit of 2048.
134 The identifiers are represented and generated in conformance with the DCE 1.1
138 system call is itself not part of the specification.
142 system call first appeared in