uuidgen(2) - NetBSD Manual Pages

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UUIDGEN(2)                NetBSD System Calls Manual                UUIDGEN(2)


NAME

     uuidgen -- generate universally unique identifiers


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

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

     int
     uuidgen(struct uuid *store, int count);


DESCRIPTION

     The uuidgen() system call generates count universally unique identifiers
     (UUIDs) and writes them to the buffer pointed to by store.  The identi-
     fiers 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 follow-
     ing 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 sig-
                                nificant 28 bits of the 60-bit timestamp.
                                This field is stored in the native byte-order.

     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 multiplexed with a 2-bit vari-
                                ant 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 field.

     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 inter-
                                face 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.


RETURN VALUES

     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.


ERRORS

     The uuidgen() system call can fail with:

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

     [EINVAL]           The count argument is less than 1 or larger than the
                        hard upper limit of 2048.


SEE ALSO

     uuidgen(1), uuid(3)

     P. Leach, M. Mealling, and R. Salz, A Universally Unique IDentifier
     (UUID) URN Namespace, IETF, RFC 4122, July 2005.


STANDARDS

     The identifiers are represented and generated in conformance with IETF
     RFC 4122, based on the historic DCE 1.1 RPC specification of the Open
     Software Foundation (now the Open Group).  The uuidgen() system call is
     itself not part of the specification.


HISTORY

     The uuidgen() system call first appeared in FreeBSD 5.0 and was subse-
     quently added to NetBSD 2.0.  It was changed to use version 4 UUIDs, i.e.
     randomly generated UUIDs, in NetBSD 8.0.

NetBSD 10.99                     May 26, 2002                     NetBSD 10.99