Identifier

/ˈjuː aɪ diː/

noun — "universally unique identifier for storage or objects."

UUID, short for Universally Unique Identifier, is a standardized 128-bit identifier used in computing to uniquely identify objects, filesystems, devices, or records without requiring a central registration authority. UUIDs are designed to be unique across both space and time, ensuring that identifiers generated independently will not collide.

Technically, a UUID consists of 128 bits, typically represented in 32 hexadecimal digits, displayed in five groups separated by hyphens, for example: 550e8400-e29b-41d4-a716-446655440000. The specification defines multiple versions, including version 1 (time-based, using MAC address and timestamp), version 3 (name-based using MD5 hashing), version 4 (randomly generated), and version 5 (name-based using SHA-1 hashing). Each version provides trade-offs between predictability, randomness, and uniqueness.

Operationally, UUIDs are used in a wide range of contexts. In filesystems such as EXT4 or NTFS, partitions are assigned UUIDs to ensure consistent mounting regardless of device path changes. In databases, UUIDs serve as primary keys for distributed systems to avoid conflicts when merging data from multiple nodes. In software systems, they identify sessions, transactions, devices, and components uniquely. Generating a UUID typically involves using standard libraries in programming languages or operating system utilities like uuidgen on Linux or New-Guid in PowerShell.

Example of generating a version 4 UUID in Python:

import uuid
unique_id = uuid.uuid4()
print(unique_id)

In practice, UUIDs provide reliable uniqueness across distributed systems, avoiding collisions even when objects are created in different machines, datacenters, or at different times. They are integral to filesystems, databases, application sessions, networked services, and configuration management. Their standardized format ensures interoperability and long-term consistency.

Conceptually, a UUID is like a digital fingerprint stamped on an object: it is effectively impossible for two objects, even created independently anywhere in the world, to have the same mark, making identification unambiguous.

See FileSystem, NTFS, EXT4, Partition Table, LBA.