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NAME

     uuidgen - generate universally unique identifiers

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #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
     identifiers are generated according to the syntax 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 multicast address is generated
     for each invocation of the system 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
     unique.

     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-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
                                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 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
                                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.

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)

STANDARDS

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

HISTORY

     The uuidgen() system call first appeared in FreeBSD 5.0.