More Nix Environment Variables and XDG Base Directories

- [`NIX_USER_CONF_FILES`](#env-NIX_USER_CONF_FILES) Overrides the location of the Nix user configuration files to load from. The default are the locations according to the [XDG Base Directory Specification]. See the [XDG Base Directories](#xdg-base-directories) sub-section for details. The variable is treated as a list separated by the `:` token. - [`TMPDIR`](#env-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`](#env-NIX_REMOTE) This variable should be set to `daemon` if you want to use the Nix daemon to execute Nix operations. This is necessary in [multi-user Nix installations](@docroot@/installation/multi-user.md). If the Nix 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`](#env-NIX_SHOW_STATS) If set to `1`, Nix will print some evaluation statistics, such as the number of values allocated. - [`NIX_COUNT_CALLS`](#env-NIX_COUNT_CALLS) If set to `1`, Nix will print how often functions were called during Nix expression evaluation. This is useful for profiling your Nix expressions. - [`GC_INITIAL_HEAP_SIZE`](#env-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 Nix follows the [XDG Base Directory Specification]. For backwards compatibility, Nix commands will follow the standard only when [`use-xdg-base-directories`] is enabled. [New Nix commands](@docroot@/command-ref/new-cli/nix.md) (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`]{#env-XDG_CONFIG_HOME} (default `~/.config`) - [`XDG_STATE_HOME`]{#env-XDG_STATE_HOME} (default `~/.local/state`) - [`XDG_CACHE_HOME`]{#env-XDG_CACHE_HOME} (default `~/.cache`) In addition, setting the following environment variables overrides the XDG base directories: - [`NIX_CONFIG_HOME`]{#env-NIX_CONFIG_HOME} (default `$XDG_CONFIG_HOME/nix`) - [`NIX_STATE_HOME`]{#env-NIX_STATE_HOME} (default `$XDG_STATE_HOME/nix`) - [`NIX_CACHE_HOME`]{#env-NIX_CACHE_HOME} (default `$XDG_CACHE_HOME/nix`) When [`use-xdg-base-directories`] is enabled, the configuration directory is: 1. `$NIX_CONFIG_HOME`, if it is defined 2. Otherwise, `$XDG_CONFIG_HOME/nix`, if `XDG_CONFIG_HOME` is defined 3. Otherwise, `~/.config/nix`. Likewise for the state and cache directories.

This section describes additional Nix environment variables, including `NIX_USER_CONF_FILES` (location of user configuration files), `TMPDIR` (directory for temporary files), `NIX_REMOTE` (use of the Nix daemon), `NIX_SHOW_STATS` (prints evaluation statistics), `NIX_COUNT_CALLS` (counts function calls during evaluation), and `GC_INITIAL_HEAP_SIZE` (initial heap size for the Boehm garbage collector). It also explains Nix's adherence to the XDG Base Directory Specification for locating configuration, state, and cache files, detailing how environment variables like `XDG_CONFIG_HOME`, `XDG_STATE_HOME`, `XDG_CACHE_HOME`, `NIX_CONFIG_HOME`, `NIX_STATE_HOME`, and `NIX_CACHE_HOME` influence these locations.