.::uuid(3)

📦
version 1.6.2 · 2 versions
, in centos-stream 10, centos-stream 9, fedora 43, fedora 44

.::uuid(3) — Universally Unique Identifier 💖

okay bestie so you found .::uuid(3) and honestly? iconic choice. this is the OSSP uuid manpage, and it's your girl's whole personality. grab a boba, we're doing this. 🧋✨

✨ NAME ✨

OSSP uuid — Universally Unique Identifier. that's it, that's the whole name. short, sweet, slays. 💅

🌸 VERSION 🌸

OSSP uuid 1.6.2 (04-Jul-2008)

yes she's a lil vintage (2008 called, she answered, and she still eats) but she's stable and we love her for it. 🫶

👑 DESCRIPTION 👑

okay so OSSP uuid is an ISO-C:1999 application programming interface (API) plus a matching command line interface (CLI), and the whole point of her is generating Universally Unique Identifier (UUID)s that are compliant with DCE 1.1, ISO/IEC 11578:1996 and IETF RFC-4122. no cap. she supports DCE 1.1 variant UUIDs of:

  • version 1 (time and node based)
  • version 3 (name based, MD5)
  • version 4 (random number based)
  • version 5 (name based, SHA-1)

and there's extra API bindings for the languages ISO-C++:1998, Perl:5 and PHP:4/5. also, if you're living in the past (affectionate), there's optional backward compatibility for the ISO-C DCE-1.1 and Perl Data::UUID APIs. we got you. 💜

so what even is a UUID? it's a 128 bit number that's designed to have a high likelihood of uniqueness over space and time, and it's computationally difficult to guess. the whole vibe is: globally unique identifiers that you can generate locally without having to phone up some global registration authority like it's the DMV. UUIDs are meant to be unique identifiers for two very different situations — mass tagging objects with an extremely short lifetime, and reliably identifying very persistent objects across a network. versatility? she has it. 🌈

and just to be super clear: this page right here? this is the ISO-C application programming interface (API) of OSSP uuid. 💅

💫 UUID Binary Representation 💫

per the DCE 1.1, ISO/IEC 11578:1996 and IETF RFC-4122 standards, a DCE 1.1 variant UUID is a 128 bit number defined out of 7 fields, each field a multiple of an octet in size, stored in network byte order. here's the diagram, and yes she's beautiful:

                                                           [4]
                                                          version
                                                        -->|  |<--
                                                           |  |
                                                           |  |  [16]
                       [32]                      [16]      |  |time_hi
                     time_low                  time_mid    | _and_version
           |<---------------------------->||<------------>||<------------>|
           | MSB                          ||              ||  |           |
           | /                            ||              ||  |           |
           |/                             ||              ||  |           |

           +------++------++------++------++------++------++------++------+~~
           |  15  ||  14  ||  13  ||  12  ||  11  ||  10  |####9  ||   8  |
           | MSO  ||      ||      ||      ||      ||      |####   ||      |
           +------++------++------++------++------++------++------++------+~~
           7654321076543210765432107654321076543210765432107654321076543210

         ~~+------++------++------++------++------++------++------++------+
           ##* 7  ||   6  ||   5  ||   4  ||   3  ||   2  ||   1  ||   0  |
           ##*    ||      ||      ||      ||      ||      ||      ||  LSO |
         ~~+------++------++------++------++------++------++------++------+
           7654321076543210765432107654321076543210765432107654321076543210

           | |    ||      ||                                             /|
           | |    ||      ||                                            / |
           | |    ||      ||                                          LSB |
           |<---->||<---->||<-------------------------------------------->|
           |clk_seq clk_seq                      node
           |_hi_res _low                         [48]
           |[5-6]    [8]
           | |
        -->| |<--
         variant
          [2-3]

example time 🍓: a UUID binary representation can be the octet stream 0xF8 0x1D 0x4F 0xAE 0x7D 0xEC 0x11 0xD0 0xA7 0x65 0x00 0xA0 0xC9 0x1E 0x6B 0xF6.

and this binary representation format is exactly what the OSSP uuid API functions uuid_import() and uuid_export() deal with under UUID_FMT_BIN. periodt. 💅

🦋 UUID ASCII String Representation 🦋

per DCE 1.1, ISO/IEC 11578:1996 and IETF RFC-4122, a DCE 1.1 variant UUID is represented as an ASCII string made of 8 hexadecimal digits, then a hyphen, then three groups of 4 hexadecimal digits each with a hyphen after, then 12 hexadecimal digits. formally, the string representation is defined by this grammar — copy it, love it, don't touch it:

 uuid                        = <time_low> "-"
                               <time_mid> "-"
                               <time_high_and_version> "-"
                               <clock_seq_high_and_reserved>
                               <clock_seq_low> "-"
                               <node>
 time_low                    = 4*<hex_octet>
 time_mid                    = 2*<hex_octet>
 time_high_and_version       = 2*<hex_octet>
 clock_seq_high_and_reserved = <hex_octet>
 clock_seq_low               = <hex_octet>
 node                        = 6*<hex_octet>
 hex_octet                   = <hex_digit> <hex_digit>
 hex_digit                   = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"
                              |"a"|"b"|"c"|"d"|"e"|"f"
                              |"A"|"B"|"C"|"D"|"E"|"F"

example: "f81d4fae-7dec-11d0-a765-00a0c91e6bf6" ✨ and this string representation format is exactly what uuid_import() and uuid_export() deal with under UUID_FMT_STR.

notice 👀 — you can also generate a URL out of an ASCII string representation of a UUID by prefixing it with "urn:uuid:", like "urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6".

🎀 UUID Single Integer Value Representation 🎀

per ISO/IEC 11578:1996 and ITU-T Rec. X.667, a DCE 1.1 variant UUID can also be represented as a single integer value — a decimal number with up to 39 digits.

example: "329800735698586629295641978511506172918". and yes, this string representation format is exactly what uuid_import() and uuid_export() deal with under UUID_FMT_SIV. 🫶

notice again 👀 — you can generate a corresponding ISO OID under the "{joint-iso-itu-t(2) uuid(25)}" arc out of a single integer value representation of a UUID by prefixing it with "2.25.". example OID: "2.25.329800735698586629295641978511506172918". and if you wanna go even further, you can make a URL by further prefixing with "urn:oid:", like "urn:oid:2.25.329800735698586629295641978511506172918". layers, bestie. layers. 💅

🌈 UUID Variants and Versions 🌈

a UUID has a variant and a version. the variant defines the layout of the UUID. the version defines the content. the only UUID variant supported in OSSP uuid is the DCE 1.1 variant. and the DCE 1.1 UUID variant versions supported in OSSP uuid are:

⭐ Version 1 (time and node based)

these are the classical UUIDs, created out of a 60-bit system time, a 14-bit local clock sequence, and a 48-bit system MAC address. that MAC address can be either the real one of a physical network interface card (NIC), or a random multi-cast MAC address. version 1 UUIDs are usually used as one-time global unique identifiers.

⭐ Version 3 (name based, MD5)

these are UUIDs based on the 128-bit MD5 message digest of the concatenation of a 128-bit namespace UUID and a name string of arbitrary length. version 3 UUIDs are usually used for non-unique but repeatable message digest identifiers.

⭐ Version 4 (random data based)

these are UUIDs based on just 128-bit of random data. version 4 UUIDs are usually used as one-time local unique identifiers.

⭐ Version 5 (name based, SHA-1)

these are UUIDs based on the 160-bit SHA-1 message digest of the concatenation of a 128-bit namespace UUID and a name string of arbitrary length. version 5 UUIDs are usually used for non-unique but repeatable message digest identifiers.

💜 UUID Uniqueness 💜

version 1 UUIDs are guaranteed to be unique through combinations of hardware addresses, time stamps and random seeds. there's a reference in the UUID to the hardware (MAC) address of the first network interface card (NIC) on the host which generated the UUID — and the tea on that reference is that it's intended to ensure the UUID will be unique in space, since the MAC address of every network card is assigned by a single global authority (IEEE) and is guaranteed to be unique. the next component in a UUID is a timestamp, and since clocks always (should) move forward, that's what makes it unique in time. and just in case some part of the above goes wrong (the hardware address can't be determined, or the clock moved steps backward 😭), there's a random clock sequence component placed into the UUID as a "catch-all" for uniqueness. she plans ahead. queen behavior. 👑

version 3 and version 5 UUIDs are guaranteed to be inherently globally unique if the combination of namespace and name used to generate them is unique.

version 4 UUIDs are not guaranteed to be globally unique, because they're generated out of locally gathered pseudo-random numbers only. nevertheless, there's still a high likelihood of uniqueness over space and time, and they're computationally difficult to guess. so like. probably fine. probably. 🙈

💀 Nil UUID 💀

there's a special Nil UUID consisting of all octets set to zero in the binary representation. it can be used as a special UUID value which does not conflict with real UUIDs. the void UUID. the blank canvas. she's giving minimalist. 🎀

💖 APPLICATION PROGRAMMING INTERFACE 💖

okay bestie, so the ISO-C Application Programming Interface (API) of OSSP uuid is literally made of these components. no cap.

✨ CONSTANTS ✨

The following constants are provided:

  • UUID_VERSION — the hexadecimal encoded OSSP uuid version. This lets you do compile-time checking of the OSSP uuid version. For run-time checking, use uuid_version() instead, periodt.

The hexadecimal encoding for a version "$v.$r$t$l" is calculated with the GNU shtool version command and is (in Perl-style for concise description) sprintf('0x%x%02x%d%02x', $v, $r, {qw(s 9 . 2 b 1 a 0)}->{$t}, ($t eq 's' ? 99 : $l)), i.e., the version 0.9.6 is encoded as "0x009206". iconic.

  • UUID_LEN_BIN, UUID_LEN_STR, UUID_LEN_SIV — the number of octets of the UUID binary and string representations. Notice that the lengths of the string representation (UUID_LEN_STR) and the lengths of the single integer value representation (UUID_LEN_SIV) does not include the necessary NUL termination character. 💅
  • UUID_MAKE_V1, UUID_MAKE_V3, UUID_MAKE_V4, UUID_MAKE_V5, UUID_MAKE_MC — the mode bits for use with uuid_make(). The UUID_MAKE_VN specify which UUID version to generate. The UUID_MAKE_MC forces the use of a random multi-cast MAC address instead of the real physical MAC address in version 1 UUIDs.
  • UUID_RC_OK, UUID_RC_ARG, UUID_RC_MEM, UUID_RC_SYS, UUID_RC_INT, UUID_RC_IMP — the possible numerical return-codes of API functions. The UUID_RC_OK indicates success, the others indicate errors. Use uuid_error() to translate them into string versions.
  • UUID_FMT_BIN, UUID_FMT_STR, UUID_FMT_SIV, UUID_FMT_TXT — the fmt formats for use with uuid_import() and uuid_export(). The UUID_FMT_BIN indicates the UUID binary representation (of length UUID_LEN_BIN), the UUID_FMT_STR indicates the UUID string representation (of length UUID_LEN_STR), the UUID_FMT_SIV indicates the UUID single integer value representation (of maximum length UUID_LEN_SIV) and the UUID_FMT_TXT indicates the textual description (of arbitrary length) of a UUID.

🌸 FUNCTIONS 🌸

The following functions are provided:

uuid_rc_t uuid_create(uuid_t **uuid);

Create a new UUID object and store a pointer to it in *uuid. A UUID object consists of an internal representation of a UUID, the internal PRNG and MD5 generator contexts, and cached MAC address and timestamp information. The initial UUID is the Nil UUID. slay.

uuid_rc_t uuid_destroy(uuid_t *uuid);

Destroy UUID object uuid. bye bestie 💀

uuid_rc_t uuid_clone(const uuid_t *uuid, uuid_t **uuid_clone);

Clone UUID object uuid and store new UUID object in uuid_clone. twin energy.

uuid_rc_t uuid_isnil(const uuid_t *uuid, int *result);

Checks whether the UUID in uuid is the Nil UUID. If this is the case, it returns true in *result. Else it returns false in *result.

uuid_rc_t uuid_compare(const uuid_t *uuid, const uuid_t *uuid2, int *result);

Compares the order of the two UUIDs in uuid1 and uuid2 and returns the result in *result: -1 if uuid1 is smaller than uuid2, 0 if uuid1 is equal to uuid2 and +1 if uuid1 is greater than uuid2. ranking, fr fr.

uuid_rc_t uuid_import(uuid_t *uuid, uuid_fmt_t fmt, const void *data_ptr, size_t data_len);

Imports a UUID uuid from an external representation of format fmt. The data is read from the buffer at data_ptr which contains at least data_len bytes.

The format of the external representation is specified by fmt and the minimum expected length in data_len depends on it. Valid values for fmt are UUID_FMT_BIN, UUID_FMT_STR and UUID_FMT_SIV.

uuid_rc_t uuid_export(const uuid_t *uuid, uuid_fmt_t fmt, void *data_ptr, size_t *data_len);

Exports a UUID uuid into an external representation of format fmt. Valid values for fmt are UUID_FMT_BIN, UUID_FMT_STR, UUID_FMT_SIV and UUID_FMT_TXT.

The data is written to the buffer whose location is obtained by dereferencing data_ptr after a "cast" to the appropriate pointer-to-pointer type. Hence the generic pointer argument data_ptr is expected to be a pointer to a "pointer of a particular type", i.e., it has to be of type "unsigned char **" for UUID_FMT_BIN and "char **" for UUID_FMT_STR, UUID_FMT_SIV and UUID_FMT_TXT.

The buffer has to be room for at least *data_len bytes. If the value of the pointer after "casting" and dereferencing data_ptr is NULL, data_len is ignored as input and a new buffer is allocated and returned in the pointer after "casting" and dereferencing data_ptr (the caller has to free(3) it later on).

If data_len is not NULL, the number of available bytes in the buffer has to be provided in *data_len and the number of actually written bytes are returned in *data_len again. The minimum required buffer length depends on the external representation as specified by fmt and is at least UUID_LEN_BIN for UUID_FMT_BIN, UUID_LEN_STR for UUID_FMT_STR and UUID_LEN_SIV for UUID_FMT_SIV. For UUID_FMT_TXT a buffer of unspecified length is required and hence it is recommended to allow OSSP uuid to allocate the buffer as necessary.

uuid_rc_t uuid_load(uuid_t *uuid, const char *name);

Loads a pre-defined UUID value into the UUID object uuid. The following name arguments are currently known:

name      UUID
nil       00000000-0000-0000-0000-000000000000
ns:DNS    6ba7b810-9dad-11d1-80b4-00c04fd430c8
ns:URL    6ba7b811-9dad-11d1-80b4-00c04fd430c8
ns:OID    6ba7b812-9dad-11d1-80b4-00c04fd430c8
ns:X500   6ba7b814-9dad-11d1-80b4-00c04fd430c8

The "ns:XXX" are names of pre-defined name-space UUIDs for use in the generation of DCE 1.1 version 3 and version 5 UUIDs. so useful.

uuid_rc_t uuid_make(uuid_t *uuid, unsigned int mode, ...);

Generates a new UUID in uuid according to mode and optional arguments (dependent on mode).

If mode contains the UUID_MAKE_V1 bit, a DCE 1.1 variant UUID of version 1 is generated. Then optionally the bit UUID_MAKE_MC forces the use of random multi-cast MAC address instead of the real physical MAC address (the default). The UUID is generated out of the 60-bit current system time, a 12-bit clock sequence and the 48-bit MAC address.

If mode contains the UUID_MAKE_V3 or UUID_MAKE_V5 bit, a DCE 1.1 variant UUID of version 3 or 5 is generated and two additional arguments are expected: first, a namespace UUID object (uuid_t *). Second, a name string of arbitrary length (const char *). The UUID is generated out of the 128-bit MD5 or 160-bit SHA-1 from the concatenated octet stream of namespace UUID and name string.

If mode contains the UUID_MAKE_V4 bit, a DCE 1.1 variant UUID of version 4 is generated. The UUID is generated out of 128-bit random data.

char *uuid_error(uuid_rc_t rc);

Returns a constant string representation corresponding to the return-code rc for use in displaying OSSP uuid errors.

unsigned long uuid_version(void);

Returns the hexadecimal encoded OSSP uuid version as compiled into the library object files. This allows run-time checking of the OSSP uuid version. For compile-time checking use UUID_VERSION instead.

🌈 EXAMPLE 🌈

The following shows an example usage of the API. Error handling is omitted for code simplification and has to be re-added for production code. no cap, don't skip error handling in prod bestie.

/* generate a DCE 1.1 v1 UUID from system environment */
char *uuid_v1(void)
{
    uuid_t *uuid;
    char *str;

    uuid_create(&uuid);
    uuid_make(uuid, UUID_MAKE_V1);
    str = NULL;
    uuid_export(uuid, UUID_FMT_STR, &str, NULL);
    uuid_destroy(uuid);
    return str;
}

/* generate a DCE 1.1 v3 UUID from an URL */
char *uuid_v3(const char *url)
{
    uuid_t *uuid;
    uuid_t *uuid_ns;
    char *str;

    uuid_create(&uuid);
    uuid_create(&uuid_ns);
    uuid_load(uuid_ns, "ns:URL");
    uuid_make(uuid, UUID_MAKE_V3, uuid_ns, url);
    str = NULL;
    uuid_export(uuid, UUID_FMT_STR, &str, NULL);
    uuid_destroy(uuid_ns);
    uuid_destroy(uuid);
    return str;
}

📚 SEE ALSO 📚

The following are references to UUID documentation and specifications:

📜 HISTORY 📜

OSSP uuid was implemented in January 2004 by Ralf S. Engelschall <rse@engelschall.com>. It was prompted by the use of UUIDs in the OSSP as and OpenPKG projects. It is a clean room implementation intended to be strictly standards compliant and maximum portable. king behavior.

🔗 SEE ALSO 🔗

uuid(1), uuid-config(1), OSSP::uuid(3).

okay that's the whole vibe. this manual page is from OSSP uuid 1.6.2, dated 04-Jul-2008, and it's the .::uuid(3) page — periodt 💅✨

📦 where this page comes from