# Common Environment Variables

Most Nix commands interpret the following environment variables:

- <span id="env-IN_NIX_SHELL">[`IN_NIX_SHELL`](#env-IN_NIX_SHELL)</span>

  Indicator that tells if the current environment was set up by
  `nix-shell`. It can have the values `pure` or `impure`.

- <span id="env-NIX_PATH">[`NIX_PATH`](#env-NIX_PATH)</span>

  A colon-separated list of search path entries used to resolve [lookup paths](@docroot@/language/constructs/lookup-path.md).

  This environment variable overrides the value of the [`nix-path` configuration setting](@docroot@/command-ref/conf-file.md#conf-nix-path).

  It can be extended using the [`-I` option](@docroot@/command-ref/opt-common.md#opt-I).

  > **Example**
  >
  > ```bash
  > $ export NIX_PATH=`/home/eelco/Dev:nixos-config=/etc/nixos
  > ```

  If `NIX_PATH` is set to an empty string, resolving search paths will always fail.

  > **Example**
  >
  > ```bash
  > $ NIX_PATH= nix-instantiate --eval '<nixpkgs>'
  > error: file 'nixpkgs' was not found in the Nix search path (add it using $NIX_PATH or -I)
  > ```

- <span id="env-NIX_IGNORE_SYMLINK_STORE">[`NIX_IGNORE_SYMLINK_STORE`](#env-NIX_IGNORE_SYMLINK_STORE)</span>

  Normally, the Nix store directory (typically `/nix/store`) is not
  allowed to contain any symlink components. This is to prevent
  “impure” builds. Builders sometimes “canonicalise” paths by
  resolving all symlink components. Thus, builds on different machines
  (with `/nix/store` resolving to different locations) could yield
  different results. This is generally not a problem, except when
  builds are deployed to machines where `/nix/store` resolves
  differently. If you are sure that you’re not going to do that, you
  can set `NIX_IGNORE_SYMLINK_STORE` to `1`.

  Note that if you’re symlinking the Nix store so that you can put it
  on another file system than the root file system, on Linux you’re
  better off using `bind` mount points, e.g.,

  ```console
  $ mkdir /nix
  $ mount -o bind /mnt/otherdisk/nix /nix
  ```

  Consult the mount 8 manual page for details.

- <span id="env-NIX_STORE_DIR">[`NIX_STORE_DIR`](#env-NIX_STORE_DIR)</span>

  Overrides the location of the Nix store (default `prefix/store`).

- <span id="env-NIX_DATA_DIR">[`NIX_DATA_DIR`](#env-NIX_DATA_DIR)</span>

  Overrides the location of the Nix static data directory (default
  `prefix/share`).

- <span id="env-NIX_LOG_DIR">[`NIX_LOG_DIR`](#env-NIX_LOG_DIR)</span>

  Overrides the location of the Nix log directory (default
  `prefix/var/log/nix`).

- <span id="env-NIX_STATE_DIR">[`NIX_STATE_DIR`](#env-NIX_STATE_DIR)</span>

  Overrides the location of the Nix state directory (default
  `prefix/var/nix`).

- <span id="env-NIX_CONF_DIR">[`NIX_CONF_DIR`](#env-NIX_CONF_DIR)</span>

  Overrides the location of the system Nix configuration directory
  (default `prefix/etc/nix`).

- <span id="env-NIX_CONFIG">[`NIX_CONFIG`](#env-NIX_CONFIG)</span>

  Applies settings from Nix configuration from the environment.
  The content is treated as if it was read from a Nix configuration file.
  Settings are separated by the newline character.