| UUIDGEN(2) | System Calls Manual | UUIDGEN(2) | 
uuidgen —
#include <sys/types.h>
#include <sys/uuid.h>
int
  
  uuidgen(struct
    uuid *store, int
    count);
uuidgen() system call generates
  count universally unique identifiers (UUIDs) and writes
  them to the buffer pointed to by store. The identifiers
  are randomly generated according to UUID version 4.
Universally unique identifiers, also known as globally unique identifiers (GUIDs), have a binary representation of 128-bits. The grouping and meaning of these bits is based on historical methods of generation from on timestamps and IEEE 802 MAC addresses, and is described by the following structure and its description of the fields that follow it:
struct uuid {
	uint32_t	time_low;
	uint16_t	time_mid;
	uint16_t	time_hi_and_version;
	uint8_t		clock_seq_hi_and_reserved;
	uint8_t		clock_seq_low;
	uint8_t		node[_UUID_NODE_LEN];
};
uuidgen() system call have variant value 10b. the
      variant value is stored in the most significant bits of the field.The binary representation is sensitive to byte ordering. Any multi-byte field is to be stored in the local or native byte-order and identifiers must be converted when transmitted to hosts that do not agree on the byte-order. The specification does not however document what this means in concrete terms and is otherwise beyond the scope of this system call.
uuidgen() system call can fail with:
P. Leach, M. Mealling, and R. Salz, A Universally Unique IDentifier (UUID) URN Namespace, IETF, RFC 4122, July 2005.
uuidgen() system
  call is itself not part of the specification.
uuidgen() system call first appeared in
  FreeBSD 5.0 and was subsequently added to
  NetBSD 2.0. It was changed to use version 4 UUIDs,
  i.e. randomly generated UUIDs, in NetBSD 8.0.
| May 26, 2002 | NetBSD 9.3 |