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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.

Debian                                            May 26, 2002                                        UUIDGEN(2)