NAME

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

SYNOPSIS

       #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

       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>.

RETURN VALUE

       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

       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>.

AUTHORS

       Theodore Y. Ts’o

SEE ALSO

       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

       For bug reports, use the issue tracker at https://github.com/util-linux/util-linux/issues.

AVAILABILITY

       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/>.