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


nix flake info - show flake metadata


nix flake info [option...] flake-url


  • Show what dwarffs resolves to:

    # nix flake metadata dwarffs
    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.


  • --json

    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.

  • --arg-from-file name path

    Pass the contents of file path as the argument name to Nix functions.

  • --arg-from-stdin name

    Pass the contents of stdin as the argument name to Nix functions.

  • --argstr name string

    Pass the string string as the argument name to Nix functions.

  • --debugger

    Start an interactive environment if evaluation fails.

  • --eval-store store-url

    The URL of the Nix store to use for evaluation, i.e. to store derivations (.drv files) and inputs referenced by them.

  • --impure

    Allow access to mutable paths and repositories.

  • --include / -I path

    Add path to the Nix search path. The Nix search path is initialized from the colon-separated NIX_PATH environment variable, and is used to look up the location of Nix expressions using paths enclosed in angle brackets (i.e., <nixpkgs>).

    For instance, passing

    -I /home/eelco/Dev
    -I /etc/nixos

    will cause Nix to look for paths relative to /home/eelco/Dev and /etc/nixos, in that order. This is equivalent to setting the NIX_PATH environment variable to


    It is also possible to match paths against a prefix. For example, passing

    -I nixpkgs=/home/eelco/Dev/nixpkgs-branch
    -I /etc/nixos

    will cause Nix to search for <nixpkgs/path> in /home/eelco/Dev/nixpkgs-branch/path and /etc/nixos/nixpkgs/path.

    If a path in the Nix search path starts with http:// or https://, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must consist of a single top-level directory. For example, passing

    -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/master.tar.gz

    tells Nix to download and use the current contents of the master branch in the nixpkgs repository.

    The URLs of the tarballs from the official nixos.org channels (see the manual page for nix-channel) can be abbreviated as channel:<channel-name>. For instance, the following two flags are equivalent:

    -I nixpkgs=channel:nixos-21.05
    -I nixpkgs=https://nixos.org/channels/nixos-21.05/nixexprs.tar.xz

    You can also fetch source trees using flake URLs and add them to the search path. For instance,

    -I nixpkgs=flake:nixpkgs

    specifies that the prefix nixpkgs shall refer to the source tree downloaded from the nixpkgs entry in the flake registry. Similarly,

    -I nixpkgs=flake:github:NixOS/nixpkgs/nixos-22.05

    makes <nixpkgs> refer to a particular branch of the NixOS/nixpkgs repository on GitHub.

  • --override-flake original-ref resolved-ref

    Override the flake registries, redirecting original-ref to resolved-ref.

  • --debug

    Set the logging verbosity level to 'debug'.

  • --log-format format

    Set the format of log output; one of raw, internal-json, bar or bar-with-logs.

  • --print-build-logs / -L

    Print full build logs on standard error.

  • --quiet

    Decrease the logging verbosity level.

  • --verbose / -v

    Increase the logging verbosity level.

Miscellaneous global options

  • --help

    Show usage information.

  • --offline

    Disable substituters and consider all previously downloaded files up-to-date.

  • --option name value

    Set the Nix configuration setting name to value (overriding nix.conf).

  • --refresh

    Consider all previously downloaded files out-of-date.

  • --repair

    During evaluation, rewrite missing or corrupted files in the Nix store. During building, rebuild missing or corrupted store paths.

  • --version

    Show version information.


See man nix.conf for overriding configuration settings with command line flags.