Glossary

builder program

The program run in a derivation. Sometimes shortened to “builder”.

derivation

A build step. A description of a program to run — called a builder program — to produce files. Derivations can depend on the results of other derivations. Derivations are created with the derivation() built-in function. See the Derivation Specification for a full reference.

store directory

A collection of build artifacts and source files, each of which is called a store object.

The conventional store directory is:

  • /opt/zb/store on Linux and macOS

  • C:\zb\store on Windows

store object

A file, directory, or symbolic link that is an immediate child of the store directory.

store path

An absolute filesystem path of a store object. See the page on Store Paths for a full reference.

realization

A mapping from derivation output to a store path. See the Realizations Binary Cache Specification for the details of the data model.

Realization can also refer to the process of producing store objects for a set of derivation outputs — the process started by a zb build command. While this is sometimes called “building”, realization may not involve running builder programs: in the case of a fully cached realization, realization would only obtain store objects from the local store and remote stores based on previous known realizations (mappings).

system value
system triple

The system value of a derivation is used to specify a class of machines that can execute the derivation’s builder. The format is intentionally compatible with LLVM target triples (which are, in turn, similar to GCC target triples). system values are a hyphen-separated collection of architecture, vendor, operating system, and environment components. Common values include:

  • x86_64-unknown-linux for Linux running on a 64-bit Intel CPU

  • aarch64-apple-macos for macOS running on a 64-bit ARM processor (Apple Silicon)

  • x86_64-pc-windows for Windows running on a 64-bit Intel CPU

The full syntax of a system value is defined in system values specification.

Nix Archive
NAR

The Nix Archive (NAR) format is a binary format for serializing files, directories, and symbolic links. The format has a single, canonical representation of file contents: it excludes file times, excludes permission bits other than executable on regular files, and has a well-defined directory listing order.

Nix Base-32

Nix uses a base-32 binary-to-text encoding for hashes and store paths. This encoding uses a custom alphabet and is not compliant with RFC 4648. The exact algorithm is specified in The Purely Functional Software Deployment Model Page 97. For compatibility, zb also uses this encoding.