uuid_generate(3) — Linux manual page


UUID_GENERATE(3)           Programmers Manual           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(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

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)

REPORTING BUGS         top

       For bug reports, use the issue tracker at

AVAILABILITY         top

       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
       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
       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 man-pages@man7.org

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)