NAME

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

SYNOPSIS

       #include <uuid/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 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 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_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 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 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 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.

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
       ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

SEE ALSO

       uuid(3),   uuidgen(1),   uuidd(8),   uuid_clear(3),   uuid_compare(3),   uuid_copy(3),   uuid_is_null(3),
       uuid_parse(3), uuid_time(3), uuid_unparse(3)

util-linux                                          May 2009                                    UUID_GENERATE(3)