2020-07-23 08:44:54 +00:00
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# Common Environment Variables
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Most Nix commands interpret the following environment variables:
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- `IN_NIX_SHELL`
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Indicator that tells if the current environment was set up by
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`nix-shell`. Since Nix 2.0 the values are `"pure"` and `"impure"`
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- `NIX_PATH`
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A colon-separated list of directories used to look up Nix
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expressions enclosed in angle brackets (i.e., `<path>`). For
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instance, the value
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/home/eelco/Dev:/etc/nixos
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will cause Nix to look for paths relative to `/home/eelco/Dev` and
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`/etc/nixos`, in this order. It is also possible to match paths
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against a prefix. For example, the value
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nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos
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will cause Nix to search for `<nixpkgs/path>` in
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`/home/eelco/Dev/nixpkgs-branch/path` and `/etc/nixos/nixpkgs/path`.
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If a path in the Nix search path starts with `http://` or
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`https://`, it is interpreted as the URL of a tarball that will be
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downloaded and unpacked to a temporary location. The tarball must
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consist of a single top-level directory. For example, setting
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`NIX_PATH` to
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nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-15.09.tar.gz
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tells Nix to download the latest revision in the Nixpkgs/NixOS 15.09
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channel.
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A following shorthand can be used to refer to the official channels:
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nixpkgs=channel:nixos-15.09
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The search path can be extended using the `-I` option, which takes
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precedence over `NIX_PATH`.
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- `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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2020-07-31 13:43:25 +00:00
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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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2020-07-23 08:44:54 +00:00
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Consult the mount 8 manual page for details.
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- `NIX_STORE_DIR`
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Overrides the location of the Nix store (default `prefix/store`).
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- `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`
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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`
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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`
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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_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`
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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`
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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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2020-07-24 13:46:16 +00:00
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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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2020-07-23 08:44:54 +00:00
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- `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`
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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`
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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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