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Common Environment Variables

Most commands in Lix interpret the following environment variables:

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

  • NIX_PATH A colon-separated list of directories used to look up the location of Nix expressions using paths enclosed in angle brackets (i.e., <path>), e.g. /home/eelco/Dev:/etc/nixos. It can be extended using the -I option.

    If NIX_PATH is not set at all, Lix will fall back to the following list in impure and unrestricted evaluation mode:

    1. $HOME/.nix-defexpr/channels
    2. nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixpkgs
    3. /nix/var/nix/profiles/per-user/root/channels

    If NIX_PATH is set to an empty string, resolving search paths will always fail. For example, attempting to use <nixpkgs> will produce:

    error: file 'nixpkgs' was not found in the Nix search path

  • NIX_IGNORE_SYMLINK_STORE 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.,

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

    Consult the mount 8 manual page for details.

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

  • NIX_DATA_DIR Overrides the location of the Lix static data directory (default prefix/share).

  • NIX_LOG_DIR Overrides the location of the Lix log directory (default prefix/var/log/nix).

  • NIX_STATE_DIR Overrides the location of the Lix state directory (default prefix/var/nix).

  • NIX_CONF_DIR Overrides the location of the system Lix configuration directory (default prefix/etc/nix).

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

  • NIX_USER_CONF_FILES Overrides the location of the Lix user configuration files to load from.

    The default are the locations according to the XDG Base Directory Specification. See the XDG Base Directories sub-section for details.

    The variable is treated as a list separated by the : token.

  • TMPDIR Use the specified directory to store temporary files. In particular, this includes temporary build directories; these can take up substantial amounts of disk space. The default is /tmp.

  • NIX_REMOTE This variable should be set to daemon if you want to use the Lix daemon to execute Nix operations. This is necessary in multi-user Nix installations. If the Lix daemon's Unix socket is at some non-standard path, this variable should be set to unix://path/to/socket. Otherwise, it should be left unset.

  • NIX_SHOW_STATS If set to 1, Lix will print some evaluation statistics, such as the number of values allocated.

  • NIX_COUNT_CALLS If set to 1, Lix will print how often functions were called during Nix expression evaluation. This is useful for profiling your Nix expressions.

  • GC_INITIAL_HEAP_SIZE If Nix has been configured to use the Boehm garbage collector, this variable sets the initial size of the heap in bytes. It defaults to 384 MiB. Setting it to a low value reduces memory consumption, but will increase runtime due to the overhead of garbage collection.

XDG Base Directories

Lix follows the XDG Base Directory Specification.

For backwards compatibility, commands in Lix will follow the standard only when [use-xdg-base-directories] is enabled. New Nix commands (experimental) conform to the standard by default.

The following environment variables are used to determine locations of various state and configuration files:

  • XDG_CONFIG_HOME (default ~/.config)
  • XDG_STATE_HOME (default ~/.local/state)
  • XDG_CACHE_HOME (default ~/.cache)