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diff --git a/doc/manual/src/command-ref/env-common.md b/doc/manual/src/command-ref/env-common.md new file mode 100644 index 000000000..03016dba7 --- /dev/null +++ b/doc/manual/src/command-ref/env-common.md @@ -0,0 +1,115 @@ +# Common Environment Variables + +Most Nix commands interpret the following environment variables: + + - `IN_NIX_SHELL` + Indicator that tells if the current environment was set up by + `nix-shell`. Since Nix 2.0 the values are `"pure"` and `"impure"` + + - `NIX_PATH` + A colon-separated list of directories used to look up Nix + expressions enclosed in angle brackets (i.e., `<path>`). For + instance, the value + + /home/eelco/Dev:/etc/nixos + + will cause Nix to look for paths relative to `/home/eelco/Dev` and + `/etc/nixos`, in this order. It is also possible to match paths + against a prefix. For example, the value + + nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos + + will cause Nix to search for `<nixpkgs/path>` in + `/home/eelco/Dev/nixpkgs-branch/path` and `/etc/nixos/nixpkgs/path`. + + If a path in the Nix search path starts with `http://` or + `https://`, it is interpreted as the URL of a tarball that will be + downloaded and unpacked to a temporary location. The tarball must + consist of a single top-level directory. For example, setting + `NIX_PATH` to + + nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-15.09.tar.gz + + tells Nix to download the latest revision in the Nixpkgs/NixOS 15.09 + channel. + + A following shorthand can be used to refer to the official channels: + + nixpkgs=channel:nixos-15.09 + + The search path can be extended using the `-I` option, which takes + precedence over `NIX_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., + + ```console + $ 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 Nix static data directory (default + `prefix/share`). + + - `NIX_LOG_DIR` + Overrides the location of the Nix log directory (default + `prefix/var/log/nix`). + + - `NIX_STATE_DIR` + Overrides the location of the Nix state directory (default + `prefix/var/nix`). + + - `NIX_CONF_DIR` + Overrides the location of the system Nix configuration directory + (default `prefix/etc/nix`). + + - `NIX_USER_CONF_FILES` + Overrides the location of the user Nix configuration files to load + from (defaults to the XDG spec locations). 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 Nix + daemon to execute Nix operations. This is necessary in [multi-user + Nix installations](../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` + If set to `1`, Nix will print some evaluation statistics, such as + the number of values allocated. + + - `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` + 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. |