FreeBSD Manual Pages
nix3-flake(1) General Commands Manual nix3-flake(1) Warning This program is experimental and its interface is subject to change. Name nix flake - manage Nix flakes Synopsis nix flake [option...] subcommand where subcommand is one of the following: * nix flake archive - copy a flake and all its inputs to a store * nix flake check - check whether the flake evaluates and run its tests * nix flake clone - clone flake repository * nix flake info - show flake metadata * nix flake init - create a flake in the current directory from a template * nix flake lock - create missing lock file entries * nix flake metadata - show flake metadata * nix flake new - create a flake in the specified directory from a tem- plate * nix flake prefetch - download the source tree denoted by a flake refer- ence into the Nix store * nix flake prefetch-inputs - fetch the inputs of a flake * nix flake show - show the outputs provided by a flake * nix flake update - update flake lock file Description nix flake provides subcommands for creating, modifying and querying Nix flakes. Flakes are the unit for packaging Nix code in a reproducible and discoverable way. They can have dependencies on other flakes, making it possible to have multi-repository Nix projects. A flake is a filesystem tree (typically fetched from a Git repository or a tarball) that contains a file named flake.nix in the root directory. flake.nix specifies some metadata about the flake such as dependencies (called inputs), as well as its outputs (the Nix values such as packages or NixOS modules provided by the flake). Flake references Flake references (flakerefs) are a way to specify the location of a flake. These have two different forms: Attribute set representation Example: { type = "github"; owner = "NixOS"; repo = "nixpkgs"; } The only required attribute is type. The supported types are listed below. URL-like syntax Example: github:NixOS/nixpkgs These are used on the command line as a more convenient alternative to the attribute set representation. For instance, in the command # nix build github:NixOS/nixpkgs#hello github:NixOS/nixpkgs is a flake reference (while hello is an output at- tribute). They are also allowed in the inputs attribute of a flake, e.g. inputs.nixpkgs.url = "github:NixOS/nixpkgs"; is equivalent to inputs.nixpkgs = { type = "github"; owner = "NixOS"; repo = "nixpkgs"; }; Following RFC 3986, characters outside of the allowed range (i.e. neither reserved characters nor unreserved characters) must be percent-encoded. Examples Here are some examples of flake references in their URL-like representa- tion: * nixpkgs: The nixpkgs entry in the flake registry. * nixpkgs/a3a3dda3bacf61e8a39258a0ed9c924eeca8e293: The nixpkgs entry in the flake registry, with its Git revision overridden to a specific value. * github:NixOS/nixpkgs: The master branch of the NixOS/nixpkgs repository on GitHub. * github:NixOS/nixpkgs/nixos-20.09: The nixos-20.09 branch of the nixpkgs repository. * github:NixOS/nixpkgs/pull/357207/head: The 357207 pull request of the nixpkgs repository. * github:NixOS/nixpkgs/a3a3dda3bacf61e8a39258a0ed9c924eeca8e293: A spe- cific revision of the nixpkgs repository. * github:edolstra/nix-warez?dir=blender: A flake in a subdirectory of a GitHub repository. * git+https://github.com/NixOS/patchelf: A Git repository. * git+https://github.com/NixOS/patchelf?ref=master: A specific branch of a Git repository. * git+https://github.com/NixOS/patchelf?ref=mas- ter&rev=f34751b88bd07d7f44f5cd3200fb4122bf916c7e: A specific branch and revision of a Git repository. * https://github.com/NixOS/patchelf/archive/master.tar.gz: A tarball flake. Path-like syntax Flakes corresponding to a local path can also be referred to by a direct path reference, either /absolute/path/to/the/flake or./rela- tive/path/to/the/flake. Note that the leading ./ is mandatory for relative paths. If it is omitted, the path will be interpreted as URL-like syntax, which will cause error messages like this: error: cannot find flake 'flake:relative/path/to/the/flake' in the flake registries The semantic of such a path is as follows: * If the directory is part of a Git repository, then the input will be treated as a git+file: URL, otherwise it will be treated as a path: url; * If the directory doesn't contain a flake.nix file, then Nix will search for such a file upwards in the file system hierarchy until it finds any of: 1. The Git repository root, or 2. The filesystem root (/), or 3. A folder on a different mount point. Contrary to URL-like references, path-like flake references can contain ar- bitrary unicode characters (except # and ?). Examples * .: The flake to which the current directory belongs. * /home/alice/src/patchelf: A flake in some other directory. * ./../sub directory/with AA+/-A(R)A(C)A'I'a~: A flake in another relative directory that has Unicode characters in its name. Flake reference attributes The following generic flake reference attributes are supported: * dir: The subdirectory of the flake in which flake.nix is located. This parameter enables having multiple flakes in a repository or tarball. The default is the root directory of the flake. * narHash: The hash of the Nix Archive (NAR) serialisation (in SRI format) of the contents of the flake. This is useful for flake types such as tarballs that lack a unique content identifier such as a Git commit hash. In addition, the following attributes are common to several flake reference types: * rev: A Git or Mercurial commit hash. * ref: A Git or Mercurial branch or tag name. Finally, some attributes are typically not specified by the user, but can occur in locked flake references and are available to Nix code: * revCount: The number of ancestors of the commit rev. * lastModified: The timestamp (in seconds since the Unix epoch) of the last modification of this version of the flake. For Git/Mercurial flakes, this is the commit time of commit rev, while for tarball flakes, it's the most recent timestamp of any file inside the tarball. Types Currently the type attribute can be one of the following: * indirect: The default. These are symbolic references to flakes that are looked up in the flake registries. These have the form [flake:]<flake-id>(/<rev-or-ref>(/rev)?)? These perform a lookup of <flake-id> in the flake registry. For ex- ample, nixpkgs and nixpkgs/release-20.09 are indirect flake refer- ences. The specified rev and/or ref are merged with the entry in the registry; see nix registry for details. For example, these are valid indirect flake references: * nixpkgs * nixpkgs/nixos-unstable * nixpkgs/a3a3dda3bacf61e8a39258a0ed9c924eeca8e293 * nixpkgs/nixos-unstable/a3a3dda3bacf61e8a39258a0ed9c924eeca8e293 * sub/dir (if a flake named sub is in the registry) * path: arbitrary local directories. The required attribute path specifies the path of the flake. The URL form is path:<path>(\?<params>)? where path is an absolute path to a directory in the file system containing a file named flake.nix. If the flake at path is not inside a git repository, the path: pre- fix is implied and can be omitted. If path is a relative path (i.e. if it does not start with /), it is interpreted as follows: * If path is a command line argument, it is interpreted relative to the current directory. * If path is used in a flake.nix, it is interpreted relative to the directory containing that flake.nix. However, the resolved path must be in the same tree. For instance, a flake.nix in the root of a tree can use path:./foo to access the flake in subdirectory foo, but path:../bar is illegal. On the other hand, a flake in the /foo directory of a tree can use path:../bar to refer to the flake in /bar. Path inputs can be specified with path values in flake.nix. Path values are a syntax for path inputs, and they are converted by 1. resolving them into relative paths, relative to the base directory of flake.nix 2. escaping URL characters (refer to IETF RFC?) 3. prepending path: Note that the allowed syntax for path values in flake inputs may be more restrictive than general Nix, so you may need to use path: if your path contains certain special characters. See Path literals Note that if you omit path:, relative paths must start with . to avoid ambiguity with registry lookups (e.g. nixpkgs is a registry lookup; ./nixpkgs is a relative path). For example, these are valid path flake references: * path:/home/user/sub/dir * /home/user/sub/dir (if dir/flake.nix is not in a git repository) * path:sub/dir * ./sub/dir * path:../parent * git: Git repositories. The location of the repository is specified by the attribute url. They have the URL form git(+http|+https|+ssh|+git|+file):(//<server>)?<path>(\?<params>)? If path starts with / (or ./ when used as an argument on the command line) and is a local path to a git repository, the leading git: or +file prefixes are implied and can be omitted. The ref attribute defaults to resolving the HEAD reference. The rev attribute must denote a commit that exists in the branch or tag specified by the ref attribute, since Nix doesn't do a full clone of the remote repository by default (and the Git protocol doesn't allow fetching a rev without a known ref). The default is the commit currently pointed to by ref. When git+file is used without specifying ref or rev, files are fetched directly from the local path as long as they have been added to the Git repository. If there are uncommitted changes, the refer- ence is treated as dirty and a warning is printed. For example, the following are valid Git flake references: * git:/home/user/sub/dir * /home/user/sub/dir (if dir/flake.nix is in a git repository) * ./sub/dir (when used on the command line and dir/flake.nix is in a git repository) * git+https://example.org/my/repo * git+https://example.org/my/repo?dir=flake1 * git+https://example.org/my/repo?shallow=1 A shallow clone of the repository. For large repositories, the shallow clone option can significantly speed up fresh clones compared to non-shallow clones, while still providing faster updates than other fetch methods such as tarball: or github:. * git+ssh://git@github.com/NixOS/nix?ref=v1.2.3 * git://github.com/edolstra/dwarffs?ref=unsta- ble&rev=e486d8d40e626a20e06d792db8cc5ac5aba9a5b4 * git+file:///home/my-user/some-repo/some-repo * mercurial: Mercurial repositories. The URL form is similar to the git type, except that the URL schema must be one of hg+http, hg+https, hg+ssh or hg+file. * tarball: Tarballs. The location of the tarball is specified by the at- tribute url. In URL form, the schema must be tarball+http://, tarball+https:// or tarball+file://. If the extension corresponds to a known archive format (.zip, .tar, .tgz, .tar.gz, .tar.xz, .tar.bz2 or .tar.zst), then the tarball+ can be dropped. This can also be used to set the location of gitea/forgejo branches. See here * file: Plain files or directory tarballs, either over http(s) or from the local disk. In URL form, the schema must be file+http://, file+https:// or file+file://. If the extension doesnat correspond to a known archive format (as defined by the tarball fetcher), then the file+ prefix can be dropped. * github: A more efficient way to fetch repositories from GitHub. The fol- lowing attributes are required: * owner: The owner of the repository. * repo: The name of the repository. These are downloaded as tarball archives, rather than through Git. This is often much faster and uses less disk space since it doesn't require fetching the entire history of the repository. On the other hand, it doesn't allow incremental fetching (but full downloads are often faster than incremental fetches!). The URL syntax for github flakes is: github:<owner>/<repo>(/<rev-or-ref>)?(\?<params>)? <rev-or-ref> specifies the name of a branch or tag (ref), or a com- mit hash (rev). Note that unlike Git, GitHub allows fetching by com- mit hash without specifying a branch or tag. You can also specify host as a parameter, to point to a custom GitHub Enterprise server. Some examples: * github:edolstra/dwarffs * github:edolstra/dwarffs/unstable * github:edolstra/dwarffs/d3f2baba8f425779026c6ec04021b2e927f61e31 * github:internal/project?host=company-github.example.org * gitlab: Similar to github, is a more efficient way to fetch GitLab repositories. The following attributes are required: * owner: The owner of the repository. * repo: The name of the repository. Like github, these are downloaded as tarball archives. The URL syntax for gitlab flakes is: gitlab:<owner>/<repo>(/<rev-or-ref>)?(\?<params>)? <rev-or-ref> works the same as github. Either a branch or tag name (ref), or a commit hash (rev) can be specified. Since GitLab allows for self-hosting, you can specify host as a parame- ter, to point to any instances other than gitlab.com. Some examples: * gitlab:veloren/veloren * gitlab:veloren/veloren/master * gitlab:veloren/veloren/80a4d7f13492d916e47d6195be23acae8001985a * gitlab:openldap/openldap?host=git.openldap.org When accessing a project in a (nested) subgroup, make sure to URL-encode any slashes, i.e. replace / with %2F: * gitlab:veloren%2Fdev/rfcs * sourcehut: Similar to github, is a more efficient way to fetch SourceHut repositories. The following attributes are required: * owner: The owner of the repository (including leading ~). * repo: The name of the repository. Like github, these are downloaded as tarball archives. The URL syntax for sourcehut flakes is: sourcehut:<owner>/<repo>(/<rev-or-ref>)?(\?<params>)? <rev-or-ref> works the same as github. Either a branch or tag name (ref), or a commit hash (rev) can be specified. Since SourceHut allows for self-hosting, you can specify host as a para- meter, to point to any instances other than git.sr.ht. Currently, ref name resolution only works for Git repositories. You can refer to Mercurial repositories by simply changing host to hg.sr.ht (or any other Mercurial instance). With the caveat that you must explicitly specify a commit hash (rev). Some examples: * sourcehut:~misterio/nix-colors * sourcehut:~misterio/nix-colors/main * sourcehut:~misterio/nix-colors?host=git.example.org * sourcehut:~misterio/nix-col- ors/182b4b8709b8ffe4e9774a4c5d6877bf6bb9a21c * sourcehut:~misterio/nix-col- ors/21c1a380a6915d890d408e9f22203436a35bb2de?host=hg.sr.ht Flake format As an example, here is a simple flake.nix that depends on the Nixpkgs flake and provides a single package (i.e. an installable derivation): { description = "A flake for building Hello World"; inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-20.03"; outputs = { self, nixpkgs }: { packages.x86_64-linux.default = # Notice the reference to nixpkgs here. with import nixpkgs { system = "x86_64-linux"; }; stdenv.mkDerivation { name = "hello"; src = self; buildPhase = "gcc -o hello ./hello.c"; installPhase = "mkdir -p $out/bin; install -t $out/bin hello"; }; }; } The following attributes are supported in flake.nix: * description: A short, one-line description of the flake. * inputs: An attrset specifying the dependencies of the flake (described below). * outputs: A function that, given an attribute set containing the outputs of each of the input flakes keyed by their identifier, yields the Nix values provided by this flake. Thus, in the example above, inputs.nixp- kgs contains the result of the call to the outputs function of the nixp- kgs flake. In addition to the outputs of each input, each input in inputs also con- tains some metadata about the inputs. These are: * outPath: The path in the Nix store of the flake's source tree. This way, the attribute set can be passed to import as if it was a path, as in the example above (import nixpkgs). * rev: The commit hash of the flake's repository, if applicable. * revCount: The number of ancestors of the revision rev. This is not available for github repositories, since they're fetched as tarballs rather than as Git repositories. * lastModifiedDate: The commit time of the revision rev, in the format %Y%m%d%H%M%S (e.g. 20181231100934). Unlike revCount, this is avail- able for both Git and GitHub repositories, so it's useful for gener- ating (hopefully) monotonically increasing version strings. * lastModified: The commit time of the revision rev as an integer de- noting the number of seconds since 1970. * narHash: The SHA-256 (in SRI format) of the Nix Archive (NAR) serial- isation NAR serialization of the flake's source tree. The value returned by the outputs function must be an attribute set. The attributes can have arbitrary values; however, various nix subcommands require specific attributes to have a specific value (e.g. pack- ages.x86_64-linux must be an attribute set of derivations built for the x86_64-linux platform). * nixConfig: a set of nix.conf options to be set when evaluating any part of a flake. In the interests of security, only a small set of set of op- tions is allowed to be set without confirmation so long as accept-flake- config is not enabled in the global configuration: * bash-prompt * bash-prompt-prefix * bash-prompt-suffix * flake-registry * commit-lock-file-summary Flake inputs The attribute inputs specifies the dependencies of a flake, as an attrset mapping input names to flake references. For example, the following speci- fies a dependency on the nixpkgs and import-cargo repositories: # A GitHub repository. inputs.import-cargo = { type = "github"; owner = "edolstra"; repo = "import-cargo"; }; # An indirection through the flake registry. inputs.nixpkgs = { type = "indirect"; id = "nixpkgs"; }; Alternatively, you can use the URL-like syntax: inputs.import-cargo.url = "github:edolstra/import-cargo"; inputs.nixpkgs.url = "nixpkgs"; Each input is fetched, evaluated and passed to the outputs function as a set of attributes with the same name as the corresponding input. The spe- cial input named self refers to the outputs and source tree of this flake. Thus, a typical outputs function looks like this: outputs = { self, nixpkgs, import-cargo }: { ... outputs ... }; It is also possible to omit an input entirely and only list it as expected function argument to outputs. Thus, outputs = { self, nixpkgs }: ...; without an inputs.nixpkgs attribute is equivalent to inputs.nixpkgs = { type = "indirect"; id = "nixpkgs"; }; Repositories that don't contain a flake.nix can also be used as inputs, by setting the input's flake attribute to false: inputs.grcov = { type = "github"; owner = "mozilla"; repo = "grcov"; flake = false; }; outputs = { self, nixpkgs, grcov }: { packages.x86_64-linux.grcov = stdenv.mkDerivation { src = grcov; ... }; }; Transitive inputs can be overridden from a flake.nix file. For example, the following overrides the nixpkgs input of the nixops input: inputs.nixops.inputs.nixpkgs = { type = "github"; owner = "my-org"; repo = "nixpkgs"; }; It is also possible to "inherit" an input from another input. This is use- ful to minimize flake dependencies. For example, the following sets the nixpkgs input of the top-level flake to be equal to the nixpkgs input of the dwarffs input of the top-level flake: inputs.nixpkgs.follows = "dwarffs/nixpkgs"; The value of the follows attribute is a /-separated sequence of input names denoting the path of inputs to be followed from the root flake. Self-attributes Flakes can declare attributes about themselves that affect how they are fetched. These attributes are specified using the special self input and are retroactively applied to it: { inputs.self.submodules = true; inputs.self.lfs = true; } The following self-attributes are supported: * submodules: A Boolean denoting whether Git submodules should be fetched when this flake is used as an input. When set to true, Git submodules will be automatically fetched without requiring callers to specify sub- modules=1 in the flake reference URL. Defaults to false. * lfs: A Boolean denoting whether Git LFS (Large File Storage) files should be fetched when this flake is used as an input. When set to true, Git LFS files will be automatically fetched. Defaults to false. These self-attributes eliminate the need for consumers of your flake to manually specify fetching options in their flake references. Overrides and follows can be combined, e.g. inputs.nixops.inputs.nixpkgs.follows = "dwarffs/nixpkgs"; sets the nixpkgs input of nixops to be the same as the nixpkgs input of dwarffs. It is worth noting, however, that it is generally not useful to eliminate transitive nixpkgs flake inputs in this way. Most flakes provide their functionality through Nixpkgs overlays or NixOS modules, which are composed into the top-level flake's nixpkgs input; so their own nixpkgs in- put is usually irrelevant. Lock files Inputs specified in flake.nix are typically "unlocked" in the sense that they don't specify an exact revision. To ensure reproducibility, Nix will automatically generate and use a lock file called flake.lock in the flake's directory. The lock file is a UTF-8 JSON file. It contains a graph struc- ture isomorphic to the graph of dependencies of the root flake. Each node in the graph (except the root node) maps the (usually) unlocked input spec- ifications in flake.nix to locked input specifications. Each node also con- tains some metadata, such as the dependencies (outgoing edges) of the node. For example, if flake.nix has the inputs in the example above, then the re- sulting lock file might be: { "version": 7, "root": "n1", "nodes": { "n1": { "inputs": { "nixpkgs": "n2", "import-cargo": "n3", "grcov": "n4" } }, "n2": { "inputs": {}, "locked": { "owner": "edolstra", "repo": "nixpkgs", "rev": "7f8d4b088e2df7fdb6b513bc2d6941f1d422a013", "type": "github", "lastModified": 1580555482, "narHash": "sha256-OnpEWzNxF/AU4KlqBXM2s5PWvfI5/BS6xQrPvkF5tO8=" }, "original": { "id": "nixpkgs", "type": "indirect" } }, "n3": { "inputs": {}, "locked": { "owner": "edolstra", "repo": "import-cargo", "rev": "8abf7b3a8cbe1c8a885391f826357a74d382a422", "type": "github", "lastModified": 1567183309, "narHash": "sha256-wIXWOpX9rRjK5NDsL6WzuuBJl2R0kUCnlpZUrASykSc=" }, "original": { "owner": "edolstra", "repo": "import-cargo", "type": "github" } }, "n4": { "inputs": {}, "locked": { "owner": "mozilla", "repo": "grcov", "rev": "989a84bb29e95e392589c4e73c29189fd69a1d4e", "type": "github", "lastModified": 1580729070, "narHash": "sha256-235uMxYlHxJ5y92EXZWAYEsEb6mm+b069GAd+BOIOxI=" }, "original": { "owner": "mozilla", "repo": "grcov", "type": "github" }, "flake": false } } } This graph has 4 nodes: the root flake, and its 3 dependencies. The nodes have arbitrary labels (e.g. n1). The label of the root node of the graph is specified by the root attribute. Nodes contain the following fields: * inputs: The dependencies of this node, as a mapping from input names (e.g. nixpkgs) to node labels (e.g. n2). * original: The original input specification from flake.nix, as a set of builtins.fetchTree arguments. * locked: The locked input specification, as a set of builtins.fetchTree arguments. Thus, in the example above, when we build this flake, the in- put nixpkgs is mapped to revision 7f8d4b088e2df7fdb6b513bc2d6941f1d422a013 of the edolstra/nixpkgs reposi- tory on GitHub. It also includes the attribute narHash, specifying the expected contents of the tree in the Nix store (as computed by nix hash-path), and may in- clude input-type-specific attributes such as the lastModified or revCount. The main reason for these attributes is to allow flake inputs to be substituted from a binary cache: narHash allows the store path to be computed, while the other attributes are necessary because they pro- vide information not stored in the store path. The attributes in locked are considered "final", meaning that they are the only ones that are passed via the arguments of the outputs function of a flake. For instance, if locked contains a lastModified attribute while the fetcher does not return a lastModified attribute, then the lastModified attribute will be passed to the outputs function. Con- versely, if locked does not contain a lastModified attribute while the fetcher does return a lastModified attribute, then no lastModified at- tribute will be passed. If locked contains a lastModified attribute and the fetcher returns a lastModified attribute, then they must have the same value. * flake: A Boolean denoting whether this is a flake or non-flake depen- dency. Corresponds to the flake attribute in the inputs attribute in flake.nix. The original and locked attributes are omitted for the root node. This is because we cannot record the commit hash or content hash of the root flake, since modifying flake.lock will invalidate these. The graph representation of lock files allows circular dependencies between flakes. For example, here are two flakes that reference each other: { inputs.b = ... location of flake B ...; # Tell the 'b' flake not to fetch 'a' again, to ensure its 'a' is # *this* 'a'. inputs.b.inputs.a.follows = ""; outputs = { self, b }: { foo = 123 + b.bar; xyzzy = 1000; }; } and { inputs.a = ... location of flake A ...; inputs.a.inputs.b.follows = ""; outputs = { self, a }: { bar = 456 + a.xyzzy; }; } Lock files transitively lock direct as well as indirect dependencies. That is, if a lock file exists and is up to date, Nix will not look at the lock files of dependencies. However, lock file generation itself does use the lock files of dependencies by default. Options 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 Nix configuration setting name to value (overriding nix.conf). * --refresh Consider all previously downloaded files out-of-date. * --version Show version information. Note See man nix.conf for overriding configuration settings with command line flags. nix3-flake(1)
Name | Synopsis | Description | Flake references | Flake format | Lock files | Options
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=nix3-flake&sektion=1&manpath=FreeBSD+Ports+15.1.quarterly>