106 lines
4.7 KiB
Markdown
106 lines
4.7 KiB
Markdown
# Common Environment Variables
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Most Nix commands interpret the following environment variables:
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- [`IN_NIX_SHELL`]{#env-IN_NIX_SHELL}\
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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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- [`NIX_PATH`]{#env-NIX_PATH}\
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A colon-separated list of directories used to look up the location of Nix
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expressions using [paths](../language/values.md#type-path)
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enclosed in angle brackets (i.e., `<path>`),
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e.g. `/home/eelco/Dev:/etc/nixos`. It can be extended using the
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[`-I` option](./opt-common.md#opt-I).
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- [`NIX_IGNORE_SYMLINK_STORE`]{#env-NIX_IGNORE_SYMLINK_STORE}\
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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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- [`NIX_STORE_DIR`]{#env-NIX_STORE_DIR}\
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Overrides the location of the Nix store (default `prefix/store`).
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- [`NIX_DATA_DIR`]{#env-NIX_DATA_DIR}\
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Overrides the location of the Nix static data directory (default
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`prefix/share`).
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- [`NIX_LOG_DIR`]{#env-NIX_LOG_DIR}\
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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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- [`NIX_STATE_DIR`]{#env-NIX_STATE_DIR}\
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Overrides the location of the Nix state directory (default
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`prefix/var/nix`).
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- [`NIX_CONF_DIR`]{#env-NIX_CONF_DIR}\
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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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- [`NIX_CONFIG`]{#env-NIX_CONFIG}\
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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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- [`NIX_USER_CONF_FILES`]{#env-NIX_USER_CONF_FILES}\
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Overrides the location of the user Nix configuration files to load
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from (defaults to the XDG spec locations). The variable is treated
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as a list separated by the `:` token.
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- [`TMPDIR`]{#env-TMPDIR}\
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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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- [`NIX_REMOTE`]{#env-NIX_REMOTE}\
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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](../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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- [`NIX_SHOW_STATS`]{#env-NIX_SHOW_STATS}\
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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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- [`NIX_COUNT_CALLS`]{#env-NIX_COUNT_CALLS}\
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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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- [`GC_INITIAL_HEAP_SIZE`]{#env-GC_INITIAL_HEAP_SIZE}\
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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 Directory
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New Nix commands conform to the [XDG Base Directory Specification], and use the following environment variables 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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Classic Nix commands can also be made to follow this standard using the [`use-xdg-base-directories`] configuration option.
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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`]: ../command-ref/conf-file.md#conf-use-xdg-base-directories |