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

Name

nix flake check - check whether the flake evaluates and run its tests

Synopsis

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

Examples

Evaluate the flake in the current directory, and build its checks:
```
# nix flake check
```
Verify that the patchelf flake evaluates, but don't build its checks:
```
# nix flake check --no-build github:NixOS/patchelf
```

Description

This command verifies that the flake specified by flake reference flake-url can be evaluated successfully (as detailed below), and that the derivations specified by the flake's checks output can be built successfully.

If the keep-going option is set to true, Lix will keep evaluating as much as it can and report the errors as it encounters them. Otherwise it will stop at the first error.

Evaluation checks

The following flake output attributes must be derivations:

checks.system.name
defaultPackage.system
devShell.system
devShells.system.name
nixosConfigurations.name.config.system.build.toplevel
packages.system.name

The following flake output attributes must be app definitions:

apps.system.name
defaultApp.system

The following flake output attributes must be template definitions:

defaultTemplate
templates.name

The following flake output attributes must be Nixpkgs overlays:

overlay
overlays.name

The following flake output attributes must be NixOS modules:

nixosModule
nixosModules.name

The following flake output attributes must be bundlers:

bundlers.name
defaultBundler

In addition, the hydraJobs output is evaluated in the same way as Hydra's hydra-eval-jobs (i.e. as a arbitrarily deeply nested attribute set of derivations). Similarly, the legacyPackages.system output is evaluated like nix-env --query --available .

Options

--all-systems Check the outputs for all systems.
--no-build Do not build checks.

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.
--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 Lix 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
```
/home/eelco/Dev:/etc/nixos
```
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 Lix 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 Lix 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.

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.
--output-lock-file flake-lock-path Write the given lock file instead of flake.lock within the top-level flake.
--override-input input-path flake-url Override a specific flake input (e.g. dwarffs/nixpkgs). This implies --no-write-lock-file.
--reference-lock-file flake-lock-path Read the given lock file instead of flake.lock within the top-level flake.

Logging-related options:

--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 Lix 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.

Note

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