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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
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27 .\" $FreeBSD: src/lib/libc/sys/uuidgen.2,v 1.7 2003/06/27 13:41:29 yar Exp $
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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
43 The
44 .Fn uuidgen
45 system call generates
46 .Fa count
47 universally unique identifiers (UUIDs) and writes them to the buffer
48 pointed to by
49 .Fa store .
50 The identifiers are generated according to the syntax and semantics of the
51 DCE version 1 variant of universally unique identifiers.
52 See below for a more in-depth description of the identifiers.
53 When no IEEE 802
54 address is available for the node field, a random multi-cast address is
55 generated for each invocation of the system call.
56 According to the algorithm of generating time-based UUIDs, this will also
57 force a new random clock sequence, thereby increasing the likelihood for
58 the identifier to be unique.
59 .Pp
60 When multiple identifiers are to be generated, the
61 .Fn uuidgen
62 system call will generate a set of identifiers that is dense in such a way
63 that there is no identifier that is larger than the smallest identifier in the
64 set and smaller than the largest identifier in the set and that is not already
65 in the set.
66 .Pp
67 Universally unique identifiers, also known as globally unique identifiers
68 (GUIDs), have a binary representation of 128-bits.
69 The grouping and meaning of these bits is described by the following
70 structure and its description of the fields that follow it:
71 .Bd -literal
72 struct 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
83 The least significant 32 bits of a 60-bit timestamp.
84 This field is stored in the native byte-order.
85 .It Va time_mid
86 The least significant 16 bits of the most significant 28 bits of the 60-bit
87 timestamp.
88 This field is stored in the native byte-order.
89 .It Va time_hi_and_version
90 The most significant 12 bits of the 60-bit timestamp multiplexed with a 4-bit
91 version number.
92 The version number is stored in the most significant 4 bits of the 16-bit
93 field.
94 This field is stored in the native byte-order.
95 .It Va clock_seq_hi_and_reserved
96 The most significant 6 bits of a 14-bit sequence number multiplexed with a
97 2-bit variant value.
98 Note that the width of the variant value is determined by the variant itself.
99 Identifiers generated by the
100 .Fn uuidgen
101 system call have variant value 10b.
102 the variant value is stored in the most significant bits of the field.
103 .It Va clock_seq_low
104 The least significant 8 bits of a 14-bit sequence number.
105 .It Va node
106 The 6-byte IEEE 802 (MAC) address of one of the interfaces of the node.
107 If no such interface exists, a random multi-cast address is used instead.
108 .El
109 .Pp
110 The binary representation is sensitive to byte ordering.
111 Any multi-byte field is to be stored in the local or native byte-order and
112 identifiers must be converted when transmitted to hosts that do not agree
113 on the byte-order.
114 The specification does not however document what this means in concrete
115 terms and is otherwise beyond the scope of this system call.
116 .Sh RETURN VALUES
117 .Rv -std
118 .Sh ERRORS
119 The
120 .Fn uuidgen
121 system call can fail with:
122 .Bl -tag -width Er
123 .It Bq Er EFAULT
124 The buffer pointed to by
125 .Fa store
126 could not be written to for any or all identifiers.
127 .It Bq Er EINVAL
128 The
129 .Fa count
130 argument 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
136 The identifiers are represented and generated in conformance with the DCE 1.1
137 RPC specification.
138 The
139 .Fn uuidgen
140 system call is itself not part of the specification.
141 .Sh HISTORY
142 The
143 .Fn uuidgen
144 system call first appeared in
145 .Fx 5.0
146 and was subsequently added to
147 .Nx 2.0 .