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157 lines
6.3 KiB
Markdown
157 lines
6.3 KiB
Markdown
# Common Environment Variables
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Most Nix commands interpret the following environment variables:
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- <span id="env-IN_NIX_SHELL">[`IN_NIX_SHELL`](#env-IN_NIX_SHELL)</span>
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Indicator that tells if the current environment was set up by
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`nix-shell`. It can have the values `pure` or `impure`.
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- <span id="env-NIX_PATH">[`NIX_PATH`](#env-NIX_PATH)</span>
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A colon-separated list of search path entries used to resolve [lookup paths](@docroot@/language/constructs/lookup-path.md).
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This environment variable overrides the value of the [`nix-path` configuration setting](@docroot@/command-ref/conf-file.md#conf-nix-path).
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It can be extended using the [`-I` option](@docroot@/command-ref/opt-common.md#opt-I).
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> **Example**
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>
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> ```bash
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> $ export NIX_PATH=`/home/eelco/Dev:nixos-config=/etc/nixos
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> ```
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If `NIX_PATH` is set to an empty string, resolving search paths will always fail.
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> **Example**
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>
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> ```bash
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> $ NIX_PATH= nix-instantiate --eval '<nixpkgs>'
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> error: file 'nixpkgs' was not found in the Nix search path (add it using $NIX_PATH or -I)
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> ```
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- <span id="env-NIX_IGNORE_SYMLINK_STORE">[`NIX_IGNORE_SYMLINK_STORE`](#env-NIX_IGNORE_SYMLINK_STORE)</span>
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Normally, the Nix store directory (typically `/nix/store`) is not
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allowed to contain any symlink components. This is to prevent
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“impure” builds. Builders sometimes “canonicalise” paths by
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resolving all symlink components. Thus, builds on different machines
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(with `/nix/store` resolving to different locations) could yield
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different results. This is generally not a problem, except when
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builds are deployed to machines where `/nix/store` resolves
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differently. If you are sure that you’re not going to do that, you
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can set `NIX_IGNORE_SYMLINK_STORE` to `1`.
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Note that if you’re symlinking the Nix store so that you can put it
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on another file system than the root file system, on Linux you’re
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better off using `bind` mount points, e.g.,
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```console
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$ mkdir /nix
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$ mount -o bind /mnt/otherdisk/nix /nix
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```
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Consult the mount 8 manual page for details.
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- <span id="env-NIX_STORE_DIR">[`NIX_STORE_DIR`](#env-NIX_STORE_DIR)</span>
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Overrides the location of the Nix store (default `prefix/store`).
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- <span id="env-NIX_DATA_DIR">[`NIX_DATA_DIR`](#env-NIX_DATA_DIR)</span>
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Overrides the location of the Nix static data directory (default
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`prefix/share`).
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- <span id="env-NIX_LOG_DIR">[`NIX_LOG_DIR`](#env-NIX_LOG_DIR)</span>
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Overrides the location of the Nix log directory (default
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`prefix/var/log/nix`).
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- <span id="env-NIX_STATE_DIR">[`NIX_STATE_DIR`](#env-NIX_STATE_DIR)</span>
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Overrides the location of the Nix state directory (default
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`prefix/var/nix`).
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- <span id="env-NIX_CONF_DIR">[`NIX_CONF_DIR`](#env-NIX_CONF_DIR)</span>
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Overrides the location of the system Nix configuration directory
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(default `prefix/etc/nix`).
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- <span id="env-NIX_CONFIG">[`NIX_CONFIG`](#env-NIX_CONFIG)</span>
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Applies settings from Nix configuration from the environment.
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The content is treated as if it was read from a Nix configuration file.
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Settings are separated by the newline character.
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- <span id="env-NIX_USER_CONF_FILES">[`NIX_USER_CONF_FILES`](#env-NIX_USER_CONF_FILES)</span>
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Overrides the location of the Nix user configuration files to load from.
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The default are the locations according to the [XDG Base Directory Specification].
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See the [XDG Base Directories](#xdg-base-directories) sub-section for details.
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The variable is treated as a list separated by the `:` token.
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- <span id="env-TMPDIR">[`TMPDIR`](#env-TMPDIR)</span>
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Use the specified directory to store temporary files. In particular,
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this includes temporary build directories; these can take up
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substantial amounts of disk space. The default is `/tmp`.
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- <span id="env-NIX_REMOTE">[`NIX_REMOTE`](#env-NIX_REMOTE)</span>
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This variable should be set to `daemon` if you want to use the Nix
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daemon to execute Nix operations. This is necessary in [multi-user
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Nix installations](@docroot@/installation/multi-user.md). If the Nix
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daemon's Unix socket is at some non-standard path, this variable
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should be set to `unix://path/to/socket`. Otherwise, it should be
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left unset.
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- <span id="env-NIX_SHOW_STATS">[`NIX_SHOW_STATS`](#env-NIX_SHOW_STATS)</span>
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If set to `1`, Nix will print some evaluation statistics, such as
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the number of values allocated.
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- <span id="env-NIX_COUNT_CALLS">[`NIX_COUNT_CALLS`](#env-NIX_COUNT_CALLS)</span>
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If set to `1`, Nix will print how often functions were called during
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Nix expression evaluation. This is useful for profiling your Nix
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expressions.
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- <span id="env-GC_INITIAL_HEAP_SIZE">[`GC_INITIAL_HEAP_SIZE`](#env-GC_INITIAL_HEAP_SIZE)</span>
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If Nix has been configured to use the Boehm garbage collector, this
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variable sets the initial size of the heap in bytes. It defaults to
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384 MiB. Setting it to a low value reduces memory consumption, but
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will increase runtime due to the overhead of garbage collection.
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## XDG Base Directories
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Nix follows the [XDG Base Directory Specification].
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For backwards compatibility, Nix commands will follow the standard only when [`use-xdg-base-directories`] is enabled.
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[New Nix commands](@docroot@/command-ref/new-cli/nix.md) (experimental) conform to the standard by default.
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The following environment variables are used to determine locations of various state and configuration files:
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- [`XDG_CONFIG_HOME`]{#env-XDG_CONFIG_HOME} (default `~/.config`)
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- [`XDG_STATE_HOME`]{#env-XDG_STATE_HOME} (default `~/.local/state`)
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- [`XDG_CACHE_HOME`]{#env-XDG_CACHE_HOME} (default `~/.cache`)
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[XDG Base Directory Specification]: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
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[`use-xdg-base-directories`]: @docroot@/command-ref/conf-file.md#conf-use-xdg-base-directories
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In addition, setting the following environment variables overrides the XDG base directories:
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- [`NIX_CONFIG_HOME`]{#env-NIX_CONFIG_HOME} (default `$XDG_CONFIG_HOME/nix`)
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- [`NIX_STATE_HOME`]{#env-NIX_STATE_HOME} (default `$XDG_STATE_HOME/nix`)
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- [`NIX_CACHE_HOME`]{#env-NIX_CACHE_HOME} (default `$XDG_CACHE_HOME/nix`)
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When [`use-xdg-base-directories`] is enabled, the configuration directory is:
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1. `$NIX_CONFIG_HOME`, if it is defined
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2. Otherwise, `$XDG_CONFIG_HOME/nix`, if `XDG_CONFIG_HOME` is defined
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3. Otherwise, `~/.config/nix`.
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Likewise for the state and cache directories.
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