Most Nix commands interpret the following environment variables: 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 that 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. 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., $ 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/log/nix). NIX_STATE_DIR Overrides the location of the Nix state directory (default prefix/var/nix). NIX_DB_DIR Overrides the location of the Nix database (default $NIX_STATE_DIR/db, i.e., prefix/var/nix/db). NIX_CONF_DIR Overrides the location of the Nix configuration directory (default prefix/etc/nix). 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_BUILD_HOOK Specifies the location of the build hook, which is a program (typically some script) that Nix will call whenever it wants to build a derivation. This is used to implement distributed builds (see ). 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. Otherwise, it should be left unset. NIX_OTHER_STORES This variable contains the paths of remote Nix installations from which packages can be copied, separated by colons. See for details. Each path should be the /nix directory of a remote Nix installation (i.e., not the /nix/store directory). The paths are subject to globbing, so you can set it so something like /var/run/nix/remote-stores/*/nix and mount multiple remote filesystems in /var/run/nix/remote-stores. Note that if you’re building through the Nix daemon, the only setting for this variable that matters is the one that the nix-daemon process uses. So if you want to change it, you have to restart the daemon. 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.