Attribute Set `lib.platforms` defines [various common lists](https://github.com/NixOS/nixpkgs/blob/master/lib/systems/doubles.nix) of platforms types.

### `badPlatforms` {#var-meta-badPlatforms}

The list of Nix [platform types](https://github.com/NixOS/nixpkgs/blob/b03ac42b0734da3e7be9bf8d94433a5195734b19/lib/meta.nix#L75-L81) on which the package is known not to be buildable.
Hydra will never create prebuilt binaries for these platform types, even if they are in [`meta.platforms`](#var-meta-platforms).
In general it is preferable to set `meta.platforms = lib.platforms.all` and then exclude any platforms on which the package is known not to build.
For example, a package which requires dynamic linking and cannot be linked statically could use this:

```nix
{
  meta.platforms = lib.platforms.all;
  meta.badPlatforms = [ lib.systems.inspect.platformPatterns.isStatic ];
}
```

The [`lib.meta.availableOn`](https://github.com/NixOS/nixpkgs/blob/b03ac42b0734da3e7be9bf8d94433a5195734b19/lib/meta.nix#L95-L106) function can be used to test whether or not a package is available (i.e. buildable) on a given platform.
Some packages use this to automatically detect the maximum set of features with which they can be built.
For example, `systemd` [requires dynamic linking](https://github.com/systemd/systemd/issues/20600#issuecomment-912338965), and [has a `meta.badPlatforms` setting](https://github.com/NixOS/nixpkgs/blob/b03ac42b0734da3e7be9bf8d94433a5195734b19/pkgs/os-specific/linux/systemd/default.nix#L752) similar to the one above.
Packages which can be built with or without `systemd` support will use `lib.meta.availableOn` to detect whether or not `systemd` is available on the [`hostPlatform`](#ssec-cross-platform-parameters) for which they are being built; if it is not available (e.g. due to a statically-linked host platform like `pkgsStatic`) this support will be disabled by default.

### `timeout` {#var-meta-timeout}

A timeout (in seconds) for building the derivation. If the derivation takes longer than this time to build, Hydra will fail it due to breaking the timeout. However, all computers do not have the same computing power, hence some builders may decide to apply a multiplicative factor to this value. When filling this value in, try to keep it approximately consistent with other values already present in `nixpkgs`.

`meta` attributes are not stored in the instantiated derivation.
Therefore, this setting may be lost when the package is used as a dependency.
To be effective, it must be presented directly to an evaluation process that handles the `meta.timeout` attribute.

### `hydraPlatforms` {#var-meta-hydraPlatforms}

The list of Nix platform types for which the [Hydra](https://github.com/nixos/hydra) [instance at `hydra.nixos.org`](https://nixos.org/hydra) will build the package. (Hydra is the Nix-based continuous build system.) It defaults to the value of `meta.platforms`. Thus, the only reason to set `meta.hydraPlatforms` is if you want `hydra.nixos.org` to build the package on a subset of `meta.platforms`, or not at all, e.g.

```nix
{
  meta.platforms = lib.platforms.linux;
  meta.hydraPlatforms = [ ];
}
```

### `broken` {#var-meta-broken}

If set to `true`, the package is marked as "broken", meaning that it won’t show up in [search.nixos.org](https://search.nixos.org/packages), and cannot be built or installed unless the environment variable [`NIXPKGS_ALLOW_BROKEN`](#opt-allowBroken) is set.
Such unconditionally-broken packages should be removed from Nixpkgs eventually unless they are fixed.

The value of this attribute can depend on a package's arguments, including `stdenv`.
This means that `broken` can be used to express constraints, for example:

- Does not cross compile

  ```nix
  { meta.broken = !(stdenv.buildPlatform.canExecute stdenv.hostPlatform); }
  ```

- Broken if all of a certain set of its dependencies are broken

  ```nix
  {
    meta.broken = lib.all (
      map (p: p.meta.broken) [
        glibc
        musl