# uuid_generate

## 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>.
    


## 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/>. 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
           2025-08-11. (At that time, the date of the most recent commit that
           was found in the repository was 2025-08-05.) 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 2.42-start-521-ec46  2025-08-09               _UUID_GENERATE_(3)
    


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