uuid_generate(3) — Linux manual page


UUID_GENERATE(3)               Libuuid API              UUID_GENERATE(3)

NAME         top

       uuid_generate, uuid_generate_random, uuid_generate_time,
       uuid_generate_time_safe - create a new unique UUID value

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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 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.

RETURN VALUE         top

       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.

CONFORMING TO         top

       This library generates UUIDs compatible with OSF DCE 1.1, and
       hash based UUIDs V3 and V5 compatible with RFC-4122.

AUTHORS         top

       Theodore Y. Ts'o

SEE ALSO         top

       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)

AVAILABILITY         top

       libuuid is part of the util-linux package since version 2.15.1
       and is available from

COLOPHON         top

       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
       2021-03-21.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-19.)  If you
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       manual 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)