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.\" Copyright 1999 Andreas Dilger (adilger@enel.ucalgary.ca)
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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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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, and the entire permission notice in its entirety,
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.\" including the disclaimer of warranties.
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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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.\" 3. The name of the author may not be used to endorse or promote
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.\" products derived from this software without specific prior
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.\" written permission.
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.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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.\" WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
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.\" WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
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.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
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.\" OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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.\" LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
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.\" USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
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.\" Created Wed Mar 10 17:42:12 1999, Andreas Dilger
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.TH UUID_GENERATE 3 "May 2009" "util-linux" "Libuuid API"
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uuid_generate, uuid_generate_random, uuid_generate_time,
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uuid_generate_time_safe \- create a new unique UUID value
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.B #include <uuid/uuid.h>
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.BI "void uuid_generate(uuid_t " out );
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.BI "void uuid_generate_random(uuid_t " out );
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.BI "void uuid_generate_time(uuid_t " out );
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.BI "int uuid_generate_time_safe(uuid_t " out );
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function creates a new universally unique identifier (UUID). The uuid will
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be generated based on high-quality randomness from
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if available. If it is not available, then
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will use an alternative algorithm which uses the current time, the
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local ethernet MAC address (if available), and random data generated
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using a pseudo-random generator.
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.B uuid_generate_random
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function forces the use of the all-random UUID format, even if
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a high-quality random number generator (i.e.,
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is not available, in which case a pseudo-random
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generator will be substituted. Note that the use of a pseudo-random
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generator may compromise the uniqueness of UUIDs
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generated in this fashion.
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function forces the use of the alternative algorithm which uses the
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current time and the local ethernet MAC address (if available).
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This algorithm used to be the default one used to generate UUID, but
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because of the use of the ethernet MAC address, it can leak
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information about when and where the UUID was generated. This can cause
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privacy problems in some applications, so the
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function only uses this algorithm if a high-quality source of
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randomness is not available. To guarantee uniqueness of UUIDs generated
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by concurrently running processes, the uuid library uses global
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clock state counter (if the process has permissions to gain exclusive access
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to this file) and/or the
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daemon, if it is running already or can be be spawned by the process (if
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installed and the process has enough permissions to run it). If neither of
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these two synchronization mechanisms can be used, it is theoretically possible
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that two concurrently running processes obtain the same UUID(s). To tell
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whether the UUID has been generated in a safe manner, use
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.BR uuid_generate_time_safe .
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.B uuid_generate_time_safe
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.BR uuid_generate_time ,
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except that it returns a value which denotes whether any of the synchronization
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mechanisms (see above) has been used.
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The UUID is 16 bytes (128 bits) long, which gives approximately 3.4x10^38
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unique values (there are approximately 10^80 elementary particles in
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the universe according to Carl Sagan's
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The new UUID can reasonably be considered unique among all UUIDs created
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on the local system, and among UUIDs created on other systems in the past
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The newly created UUID is returned in the memory location pointed to by
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.B uuid_generate_time_safe
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returns zero if the UUID has been generated in a safe manner, -1 otherwise.
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is part of the util-linux package since version 2.15.1 and is available from
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ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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.BR uuid_compare (3),
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.BR uuid_is_null (3),
added
removed
libuuid/man/uuid_generate.3
