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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | AUTHOR | AVAILABILITY | SEE ALSO | COLOPHON |
UUID_GENERATE(3) Libuuid API UUID_GENERATE(3)
uuid_generate, uuid_generate_random, uuid_generate_time, uuid_gener‐
ate_time_safe - create a new unique UUID value
#include <uuid.h>
void uuid_generate(uuid_t out);
void uuid_generate_random(uuid_t out);
void uuid_generate_time(uuid_t out);
int uuid_generate_time_safe(uuid_t out);
The uuid_generate function creates a new universally unique
identifier (UUID). The uuid will be generated based on high-quality
randomness from /dev/urandom, if available. If it is not available,
then uuid_generate will use an alternative algorithm which uses the
current time, the local ethernet MAC address (if available), and
random data generated using a pseudo-random generator.
The uuid_generate_random function forces the use of the all-random
UUID format, even if a high-quality random number generator (i.e.,
/dev/urandom) is not available, in which case a pseudo-random
generator will be substituted. Note that the use of a pseudo-random
generator may compromise the uniqueness of UUIDs generated in this
fashion.
The uuid_generate_time function forces the use of the alternative
algorithm which uses the current time and the local ethernet MAC
address (if available). This algorithm used to be the default one
used to generate UUID, but because of the use of the ethernet MAC
address, it can leak information about when and where the UUID was
generated. This can cause privacy problems in some applications, so
the uuid_generate function only uses this algorithm if a high-quality
source of randomness is not available. To guarantee uniqueness of
UUIDs generated by concurrently running processes, the uuid library
uses global clock state counter (if the process has permissions to
gain exclusive access to this file) and/or the uuidd daemon, if it is
running already or can be spawned by the process (if installed and
the process has enough permissions to run it). If neither of these
two synchronization mechanisms can be used, it is theoretically
possible that two concurrently running processes obtain the same
UUID(s). To tell whether the UUID has been generated in a safe
manner, use uuid_generate_time_safe.
The uuid_generate_time_safe is similar to uuid_generate_time, except
that it returns a value which denotes whether any of the
synchronization mechanisms (see above) has been used.
The UUID is 16 bytes (128 bits) long, which gives approximately
3.4x10^38 unique values (there are approximately 10^80 elementary
particles in the universe according to Carl Sagan's Cosmos). The new
UUID can reasonably be considered unique among all UUIDs created on
the local system, and among UUIDs created on other systems in the
past and in the future.
The newly created UUID is returned in the memory location pointed to
by out. uuid_generate_time_safe returns zero if the UUID has been
generated in a safe manner, -1 otherwise.
OSF DCE 1.1
Theodore Y. Ts'o
libuuid is part of the util-linux package since version 2.15.1 and is
available from https://www.kernel.org/pub/linux/utils/util-linux/.
uuidgen(1), uuid(3), uuid_clear(3), uuid_compare(3), uuid_copy(3),
uuid_is_null(3), uuid_parse(3), uuid_time(3), uuid_unparse(3),
uuidd(8)
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found at
⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
bug report for this manual page, send it to
util-linux@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2017-07-05. If you discover any rendering problems in this HTML ver‐
sion of the page, or you believe there is a better or more up-to-date
source for the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original man‐
ual page), send a mail to man-pages@man7.org
util-linux May 2009 UUID_GENERATE(3)
Pages that refer to this page: uuid(3), uuid_clear(3), uuid_compare(3), uuid_copy(3), uuid_is_null(3), uuid_parse(3), uuid_time(3), uuid_unparse(3)