UUID_GENERATE(3)						    Libuuid API 						  UUID_GENERATE(3)

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);

DESCRIPTION

       The uuid_generate function creates a new universally unique identifier (UUID).  The uuid will be generated based on high-quality randomness
       from /dev/urandom, 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 (i.e.,
       /dev/urandom) is not available, in which case a pseudo-random generator will be substituted.  Note that the use of a pseudo-random  genera-
       tor 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 UUID, 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_gener-
       ate 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 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 con-
       currently running processes obtain the same UUID(s).  To tell whether the UUID has  been  generated  in	a  safe  manner,  use  uuid_gener-
       ate_time_safe.

       The  uuid_generate_time_safe is similar to uuid_generate_time, except that it returns a value which denotes whether any of the synchroniza-
       tion 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.

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

       OSF DCE 1.1

AUTHOR

       Theodore Y. Ts'o

AVAILABILITY

       libuuid is part of the util-linux package since version 2.15.1 and is available from https://www.kernel.org/pub/linux/utils/util-linux/.

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)

util-linux							     May 2009							  UUID_GENERATE(3)