What is an UUID / GUID

An answer to "What is an UUID?" would be "A GUID" this answer wouldn't help most of us any further though.
UUID stands for Universally Unique IDentifier, GUID for Globally Unique IDentifier. The correct way to construct these identifiers is described in RFC 4122, ITU-T Rec. X.667 and ISO/IEC 11578:1996.

The main function of an UUID is being unique.

What is it used for:

UUIDs are applied for identification purposes in a number of fields in the computer industry.

Possible uses are (but are not limited to):
  • The identifiers in the windows registry.
  • Identifiers used in databases.
  • Identifiers used in RPC (COM, CORBA) (remote procedure calls)
To ensure nobody else would - by accident - provide something conflicting.

What does it look like:

UUIDs are basically 128 bit numbers, normally presented in the following hexadecimal - grouped form:

The nil UUID:

A special type of UUID is guaranteed to not be unique, and easily recognised. This is the nil UUID: 00000000-0000-0000-0000-000000000000. It can serve to clear UUIDs and as a template while cunstructing new ones.

How is an UUID made

I need an UUID

I want to know when an UUID was generated

Only for version 1 UUIDs, third group must start with a 1.

If you have improvements, contact information on the homepage of this host.
An agent adding logging to your java programs at runtime
The uptime of home.famkruithof.net
The exercises of the Enterprise Javabeans 3.0 book performed on the Sun Application Server instead of JBoss