143 lines
5.0 KiB
Groff
143 lines
5.0 KiB
Groff
.\" Copyright (c) 2002 Marcel Moolenaar
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\"
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 26, 2002
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.Dt UUIDGEN 2
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.Os
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.Sh NAME
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.Nm uuidgen
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.Nd generate universally unique identifiers
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/uuid.h
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.Ft int
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.Fn uuidgen "struct uuid *store" "int count"
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.Sh DESCRIPTION
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The
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.Fn uuidgen
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system call generates
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.Fa count
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universally unique identifiers (UUIDs) and writes them to the buffer
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pointed to by
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.Fa store .
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The identifiers are generated according to the syntax and semantics of the
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DCE version 1 variant of universally unique identifiers.
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See below for a more in-depth description of the identifiers.
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When no IEEE 802
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address is available for the node field, a random multicast address is
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generated for each invocation of the system call.
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According to the algorithm of generating time-based UUIDs, this will also
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force a new random clock sequence, thereby increasing the likelyhood for
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the identifier to be unique.
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.Pp
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When multiple identifiers are to be generated, the
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.Fn uuidgen
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system call will generate a set of identifiers that is dense in such a way
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that there is no identifier that is larger than the smallest identifier in the
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set and smaller than the largest identifier in the set and that is not already
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in the set.
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.Pp
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Universally unique identifiers, also known as globally unique identifiers
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(GUIDs), have a binary representation of 128-bits.
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The grouping and meaning of these bits is described by the following
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structure and its description of the fields that follow it:
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.Bd -literal
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struct uuid {
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uint32_t time_low;
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uint16_t time_mid;
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uint16_t time_hi_and_version;
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uint8_t clock_seq_hi_and_reserved;
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uint8_t clock_seq_low;
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uint8_t node[_UUID_NODE_LEN];
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};
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.Ed
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.Bl -tag -width ".Va clock_seq_hi_and_reserved"
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.It Va time_low
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The least significant 32 bits of a 60-bit timestamp.
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This field is stored in the native byte-order.
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.It Va time_mid
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The least significant 16 bits of the most significant 28 bits of the 60-bit
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timestamp.
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This field is stored in the native byte-order.
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.It Va time_hi_and_reserved
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The most significant 12 bits of the 60-bit timestamp multiplexed with a 4-bit
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version number.
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The version number is stored in the most significant 4 bits of the 16-bit
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field.
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This field is stored in the native byte-order.
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.It Va clock_seq_hi_and_reserved
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The most significant 6 bits of a 14-bit sequence number multiplexed with a
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2-bit variant value.
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Note that the width of the variant value is determined by the variant itself.
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Identifiers generated by the
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.Fn uuidgen
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system call have variant value 10b.
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the variant value is stored in the most significant bits of the field.
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.It Va clock_seq_low
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The least significant 8 bits of a 14-bit sequence number.
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.It Va node
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The 6-byte IEEE 802 (MAC) address of one of the interfaces of the node.
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If no such interface exists, a random multi-cast address is used instead.
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.El
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.Pp
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The binary representation is sensitive to byte ordering.
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Any multi-byte field is to be stored in the local or native byte-order and
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identifiers must be converted when transmitted to hosts that do not agree
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on the byte-order.
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The specification does not however document what this means in concrete
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terms and is otherwise beyond the scope of this system call.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The
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.Fn uuidgen
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system call can fail with:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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The buffer pointed to by
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.Fa store
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could not be written to for any or all identifiers.
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.It Bq Er EINVAL
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The
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.Fa count
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argument is less than 1 or larger than the hard upper limit of 2048.
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.El
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.Sh SEE ALSO
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.Xr uuidgen 1 ,
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.Xr uuid 3
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.Sh STANDARDS
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The identifiers are represented and generated in conformance with the DCE 1.1
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RPC specification.
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The
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.Fn uuidgen
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system call is itself not part of the specification.
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.Sh HISTORY
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The
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.Fn uuidgen
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system call first appeared in
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.Fx 5.0 .
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