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NetBSD 6.1.5 - man page for uuidgen (netbsd section 2)

UUIDGEN(2)			     BSD System Calls Manual			       UUIDGEN(2)

     uuidgen -- generate universally unique identifiers

     Standard C Library (libc, -lc)

     #include <sys/types.h>
     #include <sys/uuid.h>

     uuidgen(struct uuid *store, int count);

     The uuidgen() system call generates count universally unique identifiers (UUIDs) and writes
     them to the buffer pointed to by store.  The identifiers are generated according to the syn-
     tax and semantics of the DCE version 1 variant of universally unique identifiers.	See below
     for a more in-depth description of the identifiers.  When no IEEE 802 address is available
     for the node field, a random multi-cast address is generated for each invocation of the sys-
     tem call.	According to the algorithm of generating time-based UUIDs, this will also force a
     new random clock sequence, thereby increasing the likelihood for the identifier to be

     When multiple identifiers are to be generated, the uuidgen() system call will generate a set
     of identifiers that is dense in such a way that there is no identifier that is larger than
     the smallest identifier in the set and smaller than the largest identifier in the set and
     that is not already in the set.

     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 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];

     time_low			The least significant 32 bits of a 60-bit timestamp.  This field
				is stored in the native byte-order.

     time_mid			The least significant 16 bits of the most significant 28 bits of
				the 60-bit timestamp.  This field is stored in the native byte-

     time_hi_and_version	The most significant 12 bits of the 60-bit timestamp multiplexed
				with a 4-bit version number.  The version number is stored in the
				most significant 4 bits of the 16-bit field.  This field is
				stored in the native byte-order.

     clock_seq_hi_and_reserved	The most significant 6 bits of a 14-bit sequence number multi-
				plexed with a 2-bit variant value.  Note that the width of the
				variant value is determined by the variant itself.  Identifiers
				generated by the uuidgen() system call have variant value 10b.
				the variant value is stored in the most significant bits of the

     clock_seq_low		The least significant 8 bits of a 14-bit sequence number.

     node			The 6-byte IEEE 802 (MAC) address of one of the interfaces of the
				node.  If no such interface exists, a random multi-cast address
				is used instead.

     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.

     Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and
     the global variable errno is set to indicate the error.

     The uuidgen() system call can fail with:

     [EFAULT]		The buffer pointed to by store could not be written to for any or all

     [EINVAL]		The count argument is less than 1 or larger than the hard upper limit of

     uuidgen(1), uuid(3)

     The identifiers are represented and generated in conformance with the DCE 1.1 RPC specifica-
     tion.  The uuidgen() system call is itself not part of the specification.

     The uuidgen() system call first appeared in FreeBSD 5.0 and was subsequently added to
     NetBSD 2.0.

BSD					   May 26, 2002 				      BSD

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