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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | AUTHORS | SEE ALSO | REPORTING BUGS | AVAILABILITY |
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UUID_GENERATE(3) Programmers Manual UUID_GENERATE(3)
uuid_generate, uuid_generate_random, uuid_generate_time,
uuid_generate_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);
void uuid_generate_md5(uuid_t out, const uuid_t ns, const char
*name, size_t len);
void uuid_generate_sha1(uuid_t out, const uuid_t ns, const char
*name, size_t len);
The uuid_generate() function creates a new universally unique
identifier (UUID). The uuid will be generated based on
high-quality randomness from getrandom(2), /dev/urandom, or
/dev/random 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 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 UUIDs, 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 a global
clock state counter (if the process has permissions to gain
exclusive access to this file) and/or the uuidd(8) 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() function 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 uuid_generate_md5() and uuid_generate_sha1() functions
generate an MD5 and SHA1 hashed (predictable) UUID based on a
well-known UUID providing the namespace and an arbitrary binary
string. The UUIDs conform to V3 and V5 UUIDs per RFC-4122
<https://tools.ietf.org/html/rfc4122>.
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.
This library generates UUIDs compatible with OSF DCE 1.1, and
hash based UUIDs V3 and V5 compatible with RFC-4122
<https://tools.ietf.org/html/rfc4122>.
Theodore Y. Ts’o
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)
For bug reports, use the issue tracker at
https://github.com/util-linux/util-linux/issues.
The libuuid library is part of the util-linux package since
version 2.15.1. It can be downloaded from Linux Kernel Archive
<https://www.kernel.org/pub/linux/utils/util-linux/>. 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
[email protected]. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-06-10.) If you discover
any rendering problems in this HTML version 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 manual page),
send a mail to [email protected]
util-linux 2.39.594-1e0ad 2023-07-19 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)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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