uuid/uuid_generate.3

   1 .\" Copyright 1999 Andreas Dilger (adilger@enel.ucalgary.ca)
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  31 .\" Created  Wed Mar 10 17:42:12 1999, Andreas Dilger
  32 .TH UUID_GENERATE 3 "April 2004" "1.36"
  33 .SH NAME
  34 uuid_generate, uuid_generate_random, uuid_generate_time \- create a new unique UUID value
  35 .SH SYNOPSIS
  36 .nf
  37 .B #include <uuid/uuid.h>
  38 .sp
  39 .BI "void uuid_generate(uuid_t " out );
  40 .BI "void uuid_generate_random(uuid_t " out );
  41 .BI "void uuid_generate_time(uuid_t " out );
  42 .fi
  43 .SH DESCRIPTION
  44 The
  45 .B uuid_generate
  46 function creates a new universally unique identifier (UUID).  The uuid will
  47 be generated based on high-quality randomness from
  48 .IR /dev/urandom ,
  49 if available.  If it is not available, then
  50 .B uuid_generate
  51 will use an alternative algorithm which uses the current time, the
  52 local ethernet MAC address (if available), and random data generated
  53 using a pseudo-random generator.
  54 .sp
  55 The
  56 .B uuid_generate_random
  57 function forces the use of the all-random UUID format, even if
  58 a high-quality random number generator (i.e.,
  59 .IR /dev/urandom )
  60 is not available, in which case a pseudo-random
  61 generator will be subsituted.  Note that the use of a pseudo-random
  62 generator may compromise the uniqueness of UUID's
  63 generated in this fashion.
  64 .sp
  65 The
  66 .B uuid_generate_time
  67 function forces the use of the alternative algorithm which uses the
  68 current time and the local ethernet MAC address (if available).
  69 This algorithm used to be the default one used to generate UUID, but
  70 because of the use of the ethernet MAC address, it can leak
  71 information about when and where the UUID was generated.  This can cause
  72 privacy problems in some applications, so the
  73 .B uuid_generate
  74 function only uses this algorithm if a high-quality source of
  75 randomness is not available.
  76 .sp
  77 The UUID is 16 bytes (128 bits) long, which gives approximately 3.4x10^38
  78 unique values (there are approximately 10^80 elemntary particles in
  79 the universe according to Carl Sagan's
  80 .IR Cosmos ).
  81 The new UUID can reasonably be considered unique among all UUIDs created
  82 on the local system, and among UUIDs created on other systems in the past
  83 and in the future.
  84 .SH RETURN VALUE
  85 The newly created UUID is returned in the memory location pointed to by
  86 .IR out .
  87 .SH "CONFORMING TO"
  88 OSF DCE 1.1
  89 .SH AUTHOR
  90 Theodore Y. Ts'o
  91 .SH AVAILABILITY
  92 .UR http://e2fsprogs.sourceforge.net/
  93 http://e2fsprogs.sourceforge.net/
  94 .UE
  95 .SH "SEE ALSO"
  96 .BR uuid (3),
  97 .BR uuidgen (1),
  98 .BR uuid_clear (3),
  99 .BR uuid_compare (3),
 100 .BR uuid_copy (3),
 101 .BR uuid_is_null (3),
 102 .BR uuid_parse (3),
 103 .BR uuid_unparse (3)