If you are using Linux or macOS versions up to 10.14 (Mojave), the easiest way to install Nix is to run the following command: $ sh <(curl https://nixos.org/nix/install) If you're using macOS 10.15 (Catalina) or newer, consult the macOS installation instructions before installing. As of Nix 2.1.0, the Nix installer will always default to creating a single-user installation, however opting in to the multi-user installation is highly recommended.

To explicitly select a single-user installation on your system: sh <(curl https://nixos.org/nix/install) --no-daemon This will perform a single-user installation of Nix, meaning that /nix is owned by the invoking user. You should run this under your usual user account, not as root. The script will invoke sudo to create /nix if it doesn’t already exist. If you don’t have sudo, you should manually create /nix first as root, e.g.: $ mkdir /nix $ chown alice /nix The install script will modify the first writable file from amongst .bash_profile, .bash_login and .profile to source ~/.nix-profile/etc/profile.d/nix.sh. You can set the NIX_INSTALLER_NO_MODIFY_PROFILE environment variable before executing the install script to disable this behaviour. You can uninstall Nix simply by running: $ rm -rf /nix

The multi-user Nix installation creates system users, and a system service for the Nix daemon. Linux running systemd, with SELinux disabled macOS You can instruct the installer to perform a multi-user installation on your system: sh <(curl https://nixos.org/nix/install) --daemon The multi-user installation of Nix will create build users between the user IDs 30001 and 30032, and a group with the group ID 30000. You should run this under your usual user account, not as root. The script will invoke sudo as needed. If you need Nix to use a different group ID or user ID set, you will have to download the tarball manually and edit the install script. The installer will modify /etc/bashrc, and /etc/zshrc if they exist. The installer will first back up these files with a .backup-before-nix extension. The installer will also create /etc/profile.d/nix.sh. You can uninstall Nix with the following commands: sudo rm -rf /etc/profile/nix.sh /etc/nix /nix ~root/.nix-profile ~root/.nix-defexpr ~root/.nix-channels ~/.nix-profile ~/.nix-defexpr ~/.nix-channels # If you are on Linux with systemd, you will need to run: sudo systemctl stop nix-daemon.socket sudo systemctl stop nix-daemon.service sudo systemctl disable nix-daemon.socket sudo systemctl disable nix-daemon.service sudo systemctl daemon-reload # If you are on macOS, you will need to run: sudo launchctl unload /Library/LaunchDaemons/org.nixos.nix-daemon.plist sudo rm /Library/LaunchDaemons/org.nixos.nix-daemon.plist There may also be references to Nix in /etc/profile, /etc/bashrc, and /etc/zshrc which you may remove.

Starting with macOS 10.15 (Catalina), the root filesystem is read-only. This means /nix can no longer live on your system volume, and that you'll need a workaround to install Nix. The recommended approach, which creates an unencrypted APFS volume for your Nix store and a "synthetic" empty directory to mount it over at /nix, is least likely to impair Nix or your system. With all separate-volume approaches, it's possible something on your system (particularly daemons/services and restored apps) may need access to your Nix store before the volume is mounted. Adding additional encryption makes this more likely. If you're using a recent Mac with a T2 chip, your drive will still be encrypted at rest (in which case "unencrypted" is a bit of a misnomer). To use this approach, just install Nix with: $ sh <(curl https://nixos.org/nix/install) --darwin-use-unencrypted-nix-store-volume If you don't like the sound of this, you'll want to weigh the other approaches and tradeoffs detailed in this section. All of the known workarounds have drawbacks, but we hope better solutions will be available in the future. Some that we have our eye on are: A true firmlink would enable the Nix store to live on the primary data volume without the build problems caused by the symlink approach. End users cannot currently create true firmlinks. If the Nix store volume shared FileVault encryption with the primary data volume (probably by using the same volume group and role), FileVault encryption could be easily supported by the installer without requiring manual setup by each user.

Changing the default prefix for the Nix store is a simple approach which enables you to leave it on your root volume, where it can take full advantage of FileVault encryption if enabled. Unfortunately, this approach also opts your device out of some benefits that are enabled by using the same prefix across systems: Your system won't be able to take advantage of the binary cache (unless someone is able to stand up and support duplicate caching infrastructure), which means you'll spend more time waiting for builds. It's harder to build and deploy packages to Linux systems. It would also possible (and often requested) to just apply this change ecosystem-wide, but it's an intrusive process that has side effects we want to avoid for now.

If you like, you can also add encryption to the recommended approach taken by the installer. You can do this by pre-creating an encrypted volume before you run the installer--or you can run the installer and encrypt the volume it creates later. In either case, adding encryption to a second volume isn't quite as simple as enabling FileVault for your boot volume. Before you dive in, there are a few things to weigh: The additional volume won't be encrypted with your existing FileVault key, so you'll need another mechanism to decrypt the volume. You can store the password in Keychain to automatically decrypt the volume on boot--but it'll have to wait on Keychain and may not mount before your GUI apps restore. If any of your launchd agents or apps depend on Nix-installed software (for example, if you use a Nix-installed login shell), the restore may fail or break. On a case-by-case basis, you may be able to work around this problem by using wait4path to block execution until your executable is available. It's also possible to decrypt and mount the volume earlier with a login hook--but this mechanism appears to be deprecated and its future is unclear. You can hard-code the password in the clear, so that your store volume can be decrypted before Keychain is available. If you are comfortable navigating these tradeoffs, you can encrypt the volume with something along the lines of: alice$ diskutil apfs enableFileVault /nix -user disk

Another simple approach is using /etc/synthetic.conf to symlink the Nix store to the data volume. This option also enables your store to share any configured FileVault encryption. Unfortunately, builds that resolve the symlink may leak the canonical path or even fail. Because of these downsides, we can't recommend this approach.

This section goes into a little more detail on the recommended approach. You don't need to understand it to run the installer, but it can serve as a helpful reference if you run into trouble. In order to compose user-writable locations into the new read-only system root, Apple introduced a new concept called firmlinks, which it describes as a "bi-directional wormhole" between two filesystems. You can see the current firmlinks in /usr/share/firmlinks. Unfortunately, firmlinks aren't (currently?) user-configurable. For special cases like NFS mount points or package manager roots, synthetic.conf(5) supports limited user-controlled file-creation (of symlinks, and synthetic empty directories) at /. To create a synthetic empty directory for mounting at /nix, add the following line to /etc/synthetic.conf (create it if necessary): nix This configuration is applied at boot time, but you can use apfs.util to trigger creation (not deletion) of new entries without a reboot: alice$ /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs.util -B Create the new APFS volume with diskutil: alice$ sudo diskutil apfs addVolume diskX APFS 'Nix Store' -mountpoint /nix Using vifs, add the new mount to /etc/fstab. If it doesn't already have other entries, it should look something like: # # Warning - this file should only be modified with vifs(8) # # Failure to do so is unsupported and may be destructive. # LABEL=Nix\040Store /nix apfs rw,nobrowse The nobrowse setting will keep Spotlight from indexing this volume, and keep it from showing up on your desktop.

NixOS.org hosts version-specific installation URLs for all Nix versions since 1.11.16, at https://releases.nixos.org/nix/nix-version/install. These install scripts can be used the same as the main NixOS.org installation script: sh <(curl https://nixos.org/nix/install) In the same directory of the install script are sha256 sums, and gpg signature files.

You can also download a binary tarball that contains Nix and all its dependencies. (This is what the install script at https://nixos.org/nix/install does automatically.) You should unpack it somewhere (e.g. in /tmp), and then run the script named install inside the binary tarball: alice$ cd /tmp alice$ tar xfj nix-1.8-x86_64-darwin.tar.bz2 alice$ cd nix-1.8-x86_64-darwin alice$ ./install If you need to edit the multi-user installation script to use different group ID or a different user ID range, modify the variables set in the file named install-multi-user.