nix3-flake-metadata(1) General Commands Manual nix3-flake-metadata(1)

Warning: This program is experimental and its interface is subject to change.

nix flake metadata - show flake metadata

nix flake metadata [option…] flake-url

Show what nixpkgs resolves to:
# nix flake metadata nixpkgs
Resolved URL:  github:edolstra/dwarffs
Locked URL:    github:edolstra/dwarffs/f691e2c991e75edb22836f1dbe632c40324215c5
Description:   A filesystem that fetches DWARF debug info from the Internet on demand
Path:          /nix/store/769s05vjydmc2lcf6b02az28wsa9ixh1-source
Revision:      f691e2c991e75edb22836f1dbe632c40324215c5
Last modified: 2021-01-21 15:41:26
├───nix: github:NixOS/nix/6254b1f5d298ff73127d7b0f0da48f142bdc753c
│   ├───lowdown-src: github:kristapsdz/lowdown/1705b4a26fbf065d9574dce47a94e8c7c79e052f
│   └───nixpkgs: github:NixOS/nixpkgs/ad0d20345219790533ebe06571f82ed6b034db31
└───nixpkgs follows input 'nix/nixpkgs'
Show information about dwarffs in JSON format:
# nix flake metadata dwarffs --json | jq .
"description": "A filesystem that fetches DWARF debug info from the Internet on demand",
"lastModified": 1597153508,
"locked": {

"lastModified": 1597153508,
"narHash": "sha256-VHg3MYVgQ12LeRSU2PSoDeKlSPD8PYYEFxxwkVVDRd0=",
"owner": "edolstra",
"repo": "dwarffs",
"rev": "d181d714fd36eb06f4992a1997cd5601e26db8f5",
"type": "github" }, "locks": { ... }, "original": {
"id": "dwarffs",
"type": "indirect" }, "originalUrl": "flake:dwarffs", "path": "/nix/store/hang3792qwdmm2n0d9nsrs5n6bsws6kv-source", "resolved": {
"owner": "edolstra",
"repo": "dwarffs",
"type": "github" }, "resolvedUrl": "github:edolstra/dwarffs", "revision": "d181d714fd36eb06f4992a1997cd5601e26db8f5", "url": "github:edolstra/dwarffs/d181d714fd36eb06f4992a1997cd5601e26db8f5" }

This command shows information about the flake specified by the flake reference flake-url. It resolves the flake reference using the flake registry <./>, fetches it, and prints some meta data. This includes:

  • Resolved URL: If flake-url is a flake identifier, then this is the flake reference that specifies its actual location, looked up in the flake registry.
  • Locked URL: A flake reference that contains a commit or content hash and thus uniquely identifies a specific flake version.
  • Description: A one-line description of the flake, taken from the description field in flake.nix.
  • Path: The store path containing the source code of the flake.
  • Revision: The Git or Mercurial commit hash of the locked flake.
  • Revisions: The number of ancestors of the Git or Mercurial commit of the locked flake. Note that this is not available for github flakes.
  • Last modified: For Git or Mercurial flakes, this is the commit time of the commit of the locked flake; for tarball flakes, it’s the most recent timestamp of any file inside the tarball.
  • Inputs: The flake inputs with their corresponding lock file entries.

With --json, the output is a JSON object with the following fields:

  • original and originalUrl: The flake reference specified by the user (flake-url) in attribute set and URL representation.
  • resolved and resolvedUrl: The resolved flake reference (see above) in attribute set and URL representation.
  • locked and lockedUrl: The locked flake reference (see above) in attribute set and URL representation.
  • description: See Description above.
  • path: See Path above.
  • revision: See Revision above.
  • revCount: See Revisions above.
  • lastModified: See Last modified above.
  • locks: The contents of flake.lock.

Produce output in JSON format, suitable for consumption by another program.

Common evaluation options:

  • --arg name expr
    Pass the value expr as the argument name to Nix functions.
  • --argstr name string
    Pass the string string as the argument name to Nix functions.
  • --eval-store store-url
    The Nix store to use for evaluations.
  • --impure
    Allow access to mutable paths and repositories.
  • --include / -I path
    Add path to the list of locations used to look up <...> file names.
  • --override-flake original-ref resolved-ref
    Override the flake registries, redirecting original-ref to resolved-ref.

Common flake-related options:

  • --commit-lock-file
    Commit changes to the flake’s lock file.
  • --inputs-from flake-url
    Use the inputs of the specified flake as registry entries.
  • --no-registries
    Don’t allow lookups in the flake registries. This option is deprecated; use --no-use-registries.
  • --no-update-lock-file
    Do not allow any updates to the flake’s lock file.
  • --no-write-lock-file
    Do not write the flake’s newly generated lock file.
  • --override-input input-path flake-url
    Override a specific flake input (e.g. dwarffs/nixpkgs). This implies --no-write-lock-file.
  • --recreate-lock-file
    Recreate the flake’s lock file from scratch.
  • --update-input input-path
    Update a specific flake input (ignoring its previous entry in the lock file).