# Installing a Binary Distribution

The easiest way to install Nix is to run the following command:

```console
$ sh <(curl -L https://nixos.org/nix/install)
```

This will run the installer interactively (causing it to explain what
it is doing more explicitly), and perform the default "type" of install
for your platform:
- single-user on Linux
- multi-user on macOS

  > **Notes on read-only filesystem root in macOS 10.15 Catalina +**
  >
  > - It took some time to support this cleanly. You may see posts,
  >   examples, and tutorials using obsolete workarounds.
  > - Supporting it cleanly made macOS installs too complex to qualify
  >   as single-user, so this type is no longer supported on macOS.

We recommend the multi-user install if it supports your platform and
you can authenticate with `sudo`.

# Single User Installation

To explicitly select a single-user installation on your system:

```console
$ sh <(curl -L 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 can run this under your usual user
account or 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.:

```console
$ 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:

```console
$ rm -rf /nix
```

# Multi User Installation

The multi-user Nix installation creates system users, and a system
service for the Nix daemon.

**Supported Systems**
- Linux running systemd, with SELinux disabled
- macOS

You can instruct the installer to perform a multi-user installation on
your system:

```console
$ sh <(curl -L 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
can run this under your usual user account or root. The script
will invoke `sudo` as needed.

> **Note**
>
> 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](#installing-from-a-binary-tarball).

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`.

## Uninstalling

### Linux

If you are on Linux with systemd:

1. Remove the Nix daemon service:

   ```console
   sudo systemctl stop nix-daemon.service
   sudo systemctl disable nix-daemon.socket nix-daemon.service
   sudo systemctl daemon-reload
   ```

1. Remove systemd service files:

   ```console
   sudo rm /etc/systemd/system/nix-daemon.service /etc/systemd/system/nix-daemon.socket
   ```

1. The installer script uses systemd-tmpfiles to create the socket directory.
    You may also want to remove the configuration for that:

   ```console
   sudo rm /etc/tmpfiles.d/nix-daemon.conf
   ```

Remove files created by Nix:

```console
sudo rm -rf /nix /etc/nix /etc/profile/nix.sh ~root/.nix-profile ~root/.nix-defexpr ~root/.nix-channels ~/.nix-profile ~/.nix-defexpr ~/.nix-channels
```

Remove build users and their group:

```console
for i in $(seq 1 32); do
  sudo userdel nixbld$i
done
sudo groupdel nixbld
```

There may also be references to Nix in

- `/etc/profile`
- `/etc/bashrc`
- `/etc/zshrc`

which you may remove.

### macOS

1. Edit `/etc/zshrc` and `/etc/bashrc` to remove the lines sourcing
   `nix-daemon.sh`, which should look like this:

   ```bash
   # Nix
   if [ -e '/nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh' ]; then
     . '/nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh'
   fi
   # End Nix
   ```

   If these files haven't been altered since installing Nix you can simply put
   the backups back in place:

   ```console
   sudo mv /etc/zshrc.backup-before-nix /etc/zshrc
   sudo mv /etc/bashrc.backup-before-nix /etc/bashrc
   ```

   This will stop shells from sourcing the file and bringing everything you
   installed using Nix in scope.

2. Stop and remove the Nix daemon services:

   ```console
   sudo launchctl unload /Library/LaunchDaemons/org.nixos.nix-daemon.plist
   sudo rm /Library/LaunchDaemons/org.nixos.nix-daemon.plist
   sudo launchctl unload /Library/LaunchDaemons/org.nixos.darwin-store.plist
   sudo rm /Library/LaunchDaemons/org.nixos.darwin-store.plist
   ```

   This stops the Nix daemon and prevents it from being started next time you
   boot the system.

3. Remove the `nixbld` group and the `_nixbuildN` users:

   ```console
   sudo dscl . -delete /Groups/nixbld
   for u in $(sudo dscl . -list /Users | grep _nixbld); do sudo dscl . -delete /Users/$u; done
   ```

   This will remove all the build users that no longer serve a purpose.

4. Edit fstab using `sudo vifs` to remove the line mounting the Nix Store
   volume on `/nix`, which looks like
   `UUID=<uuid> /nix apfs rw,noauto,nobrowse,suid,owners` or
   `LABEL=Nix\040Store /nix apfs rw,nobrowse`. This will prevent automatic
   mounting of the Nix Store volume.

5. Edit `/etc/synthetic.conf` to remove the `nix` line. If this is the only
   line in the file you can remove it entirely, `sudo rm /etc/synthetic.conf`.
   This will prevent the creation of the empty `/nix` directory to provide a
   mountpoint for the Nix Store volume.

6. Remove the files Nix added to your system:

   ```console
   sudo rm -rf /etc/nix /var/root/.nix-profile /var/root/.nix-defexpr /var/root/.nix-channels ~/.nix-profile ~/.nix-defexpr ~/.nix-channels
   ```

   This gets rid of any data Nix may have created except for the store which is
   removed next.

7. Remove the Nix Store volume:

   ```console
   sudo diskutil apfs deleteVolume /nix
   ```

   This will remove the Nix Store volume and everything that was added to the
   store.

   If the output indicates that the command couldn't remove the volume, you should
   make sure you don't have an _unmounted_ Nix Store volume. Look for a
   "Nix Store" volume in the output of the following command:

   ```console
   diskutil list
   ```

   If you _do_ see a "Nix Store" volume, delete it by re-running the diskutil
   deleteVolume command, but replace `/nix` with the store volume's `diskXsY`
   identifier.

> **Note**
>
> After you complete the steps here, you will still have an empty `/nix`
> directory. This is an expected sign of a successful uninstall. The empty
> `/nix` directory will disappear the next time you reboot.
>
> You do not have to reboot to finish uninstalling Nix. The uninstall is
> complete. macOS (Catalina+) directly controls root directories and its
> read-only root will prevent you from manually deleting the empty `/nix`
> mountpoint.

# macOS Installation
[]{#sect-macos-installation-change-store-prefix}[]{#sect-macos-installation-encrypted-volume}[]{#sect-macos-installation-symlink}[]{#sect-macos-installation-recommended-notes}
<!-- Note: anchors above to catch permalinks to old explanations -->

We believe we have ironed out how to cleanly support the read-only root
on modern macOS. New installs will do this automatically.

This section previously detailed the situation, options, and trade-offs,
but it now only outlines what the installer does. You don't need to know
this to run the installer, but it may help if you run into trouble:

- create a new APFS volume for your Nix store
- update `/etc/synthetic.conf` to direct macOS to create a "synthetic"
  empty root directory to mount your volume
- specify mount options for the volume in `/etc/fstab`
  - `rw`: read-write
  - `noauto`: prevent the system from auto-mounting the volume (so the
    LaunchDaemon mentioned below can control mounting it, and to avoid
    masking problems with that mounting service).
  - `nobrowse`: prevent the Nix Store volume from showing up on your
    desktop; also keeps Spotlight from spending resources to index
    this volume
  <!-- TODO:
  - `suid`: honor setuid? surely not? ...
  - `owners`: honor file ownership on the volume

    For now I'll avoid pretending to understand suid/owners more
    than I do. There've been some vague reports of file-ownership
    and permission issues, particularly in cloud/VM/headless setups.
    My pet theory is that this has something to do with these setups
    not having a token that gets delegated to initial/admin accounts
    on macOS. See scripts/create-darwin-volume.sh for a little more.

    In any case, by Dec 4 2021, it _seems_ like some combination of
    suid, owners, and calling diskutil enableOwnership have stopped
    new reports from coming in. But I hesitate to celebrate because we
    haven't really named and catalogued the behavior, understood what
    we're fixing, and validated that all 3 components are essential.
  -->
- if you have FileVault enabled
    - generate an encryption password
    - put it in your system Keychain
    - use it to encrypt the volume
- create a system LaunchDaemon to mount this volume early enough in the
  boot process to avoid problems loading or restoring any programs that
  need access to your Nix store

# Installing a pinned Nix version from a URL

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:

```console
$ sh <(curl -L https://nixos.org/nix/install)
```

In the same directory of the install script are sha256 sums, and gpg
signature files.

# Installing from a binary tarball

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:

```console
$ cd /tmp
$ tar xfj nix-1.8-x86_64-darwin.tar.bz2
$ cd nix-1.8-x86_64-darwin
$ ./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`.
