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/>.