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uuid — generate, convert, and decode Universally Unique IDentifiers
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Description
By default, generates a UUID (Universally Unique Identifier), of a version specified by -v (default 1) in
the canonical STRing format.
With -d, decodes uuid (or reads it in from the standard input stream if "-"), yielding something akin to
encode: STR: 92a3d3de-6bbf-11ef-9f5b-774ebb537938
SIV: 194917928982963228599463962120788605240
decode: variant: DCE 1.1, ISO/IEC 11578:1996
version: 1 (time and node based)
content: time: 2024-09-05 19:46:41.491043.0 UTC
clock: 8027 (usually random)
node: 77:4e:bb:53:79:38 (local multicast)
or
encode: STR: 7e017d98-cecc-41f6-8030-552d23cd38e6
SIV: 167490467173639937831846401373276813542
decode: variant: DCE 1.1, ISO/IEC 11578:1996
version: 4 (random data based)
content: 7E:01:7D:98:CE:CC:01:F6:00:30:55:2D:23:CD:38:E6
(no semantics: random data only)
A UUID is a 128-bit (16-byte) number whose format (method of generation) makes it very likely that it
will be unique, both spatially and temporally. This makes them well-suited for identifying anything from
ephemera like database queries to databases themselves.
The three principal -Formats are:
STRing 01234567-890a-bcde-f012-3456789abcde (hexadecimal string broken up by
dashes)
SIV (Single Integer Value) 128-bit decimal integer
BINary or "raw" the 16 bytes of the UUID in big endian order (most significant first)
UUIDs come in a few -versions:
1 based on the current time (to the precision of 100ns), and the host's MAC address (this
implementation uses the MAC address of the first NIC it finds, unless -m, in which case random data
is substituted for the MAC)
6 very similar, but the most significant (slowest-changing) parts of the timestamp are stored first,
which improves locality in some database applications
7 contains the current UNIX time — versions 1 and 6 encode a UUID time which is off by like 400 years
— (to the precision of 1ms), then 10 bytes of random data.
Thisversionshouldbepreferredto1and6.3 hashes the "namespace" (first argument, either a STRing-format UUID or a well-known name (see
below)) and the "name" (second argument, arbitrary data) with the MD5(3) digest, and uses that
directly (a few branding bytes are replaced to identify the format)
5 the same as version 3, but uses the first 16 bytes of the SHA1(3) digest
4 just random data
The namespaces understood when generating version 3 and 5 UUIDs are:
uuid (any valid STRingified UUID)
nil00000000-0000-0000-0000-000000000000 — the special all-zero UUID
maxffffffff-ffff-ffff-ffff-ffffffffffff — the special all-bits-set/sorts-after-everything
sentinel UUID
ns:DNS6ba7b810-9dad-11d1-80b4-00c04fd430c8 — for fully-qualified domain names
ns:URL6ba7b811-9dad-11d1-80b4-00c04fd430c8 — for URLs
ns:OID6ba7b812-9dad-11d1-80b4-00c04fd430c8 — for ISO OIDs
ns:X5006ba7b814-9dad-11d1-80b4-00c04fd430c8 — for X.500 Distinguished Names
Examples
A web site can be uniquely identified with a version 5 (SHA-1), namespace ns:DNS UUID, and a web-page —
ns:URL (note that this information cannot be extracted, and only serves as a way to avoid collisions for
otherwise-identical names):
$uuid-v5ns:DNShinfo.network.
f50b485f-ac66-591d-b95f-2c946c5a5668
$uuid-v5ns:URLhttps://hinfo.network
8cebc56f-51d0-5323-a031-1b9258de14f8
$uuid-d8cebc56f-51d0-5323-a031-1b9258de14f8
encode: STR: f50b485f-ac66-591d-b95f-2c946c5a5668
SIV: 325719442146270326702531202385345926760
decode: variant: DCE 1.1, ISO/IEC 11578:1996
version: 5 (name based, SHA-1)
content: F5:0B:48:5F:AC:66:09:1D:39:5F:2C:94:6C:5A:56:68
(not decipherable: truncated SHA-1 message digest only)
$uuid-v7
8cebc56f-51d0-5323-a031-1b9258de14f8
$uuid-d8cebc56f-51d0-5323-a031-1b9258de14f8
encode: STR: 0191c41a-9de1-7f96-b8cb-88e4348ee74c
SIV: 2086088501348764349551890213853128524
decode: variant: DCE 1.1, ISO/IEC 11578:1996
version: 7 (UNIX time + random data)
content: time: 2024-09-05 21:32:44.385 UTC
random: 0F:96:38:CB:88:E4:34:8E:E7:4C
Name
uuid — generate, convert, and decode Universally Unique IDentifiers
Options
-ncount Generate count UUIDs. Defaults to 1.
-ooutfile Write to outfile.
-FBIN|STR|SIV Produce output in the given format. Defaults to STR.
-r-FBIN-v1|3|4|5|6|7 Version to generate. Defaults to 1.
-m-v1|6 only: ignore the current host's MAC addresses, use random data instead (this may
still happen if the if a MAC can't be determined or all MACs are multicast).
-1-v1 only, count >1 only: generate each UUID independently. Version 1 UUIDs have a field
that increases monotonically within a session; thus, for example, in
$uuid-n4
366ab5a3-6bc4-11ef-a31a-0026b986fdd4
366ab5ce-6bc4-11ef-a31b-0026b986fdd4
366ab5f8-6bc4-11ef-a31c-0026b986fdd4
366ab621-6bc4-11ef-a31d-0026b986fdd4
^^^^
the highlighted column starts random, but then increments. -1 generates each UUID de
novo.
-d Decode and parse uuid. -F sets which format to read. -FBIN is only available when
reading from the standard input stream ("-").
See Also
uuid(3), OSSP::uuid(3)
Standards
RFC9562:UniversallyUniqueIDentifiers(UUIDs): https://datatracker.ietf.org/doc/html/rfc9562
supersedes all previous standards with an unbecoming brevity.
There are many Versions, but only one useful Variant.
ossp-uuid 1.6.4 December 9, 2024 UUID(1)
Synopsis
uuid [-ncount] [-ooutfile] [-r|-FBIN|STR|SIV] [-v1] [-m1]
uuid [-ncount] [-ooutfile] [-r|-FBIN|STR|SIV] -v3uuid|nil|max|ns:{DNS|URL|OID|X500} datauuid [-ncount] [-ooutfile] [-r|-FBIN|STR|SIV] -v4uuid [-ncount] [-ooutfile] [-r|-FBIN|STR|SIV] -v5uuid|nil|max|ns:{DNS|URL|OID|X500} datauuid [-ncount] [-ooutfile] [-r|-FBIN|STR|SIV] -v6uuid [-ncount] [-ooutfile] [-r|-FBIN|STR|SIV] -v7uuid-d [-ooutfile] [ -FSTR|SIV] uuiduuid-d [-ooutfile] [-r|-FBIN|STR|SIV] -
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