Nixsa - A Nix Standalone Environment

Nixsa lets you use Nix without any installation. Just extract the tarball and you're ready to go! All state and configuration remain within the nixsa folder.

# Download the Nixsa tarball
wget https://github.com/noamraph/nixsa/releases/download/v0.2.0/nixsa-0.2.0-x86_64-linux.tar.xz

# Extract
tar -xf nixsa-0.2.0-x86_64-linux.tar.xz

# Install a package
nixsa/bin/nix profile install nixpkgs#ponysay

# Use it
nixsa/bin/ponysay 'Hi Nixsa!'

One more feature: run nixsa/bin/nixsa to start a shell where /nix is binded to nixsa/nix, and where all the commands in the Nix profile (in nixsa/state/profile) are in the PATH.

Tip: You can add the nixsa/bin folder to your $PATH, to have the installed Nix packages readily available.

How does it work?

Nixsa uses Bubblewrap, a sandboxing tool, to run the commands in an environment where /nix is binded to the nix subfolder of the nixsa folder.

All commands in nixsa/bin are symlinks to the nixsa executable, a statically-linked executable written in Rust. If the nixsa executable is called as a symlink, it uses the symlink name as the command to run. So running nixsa/bin/ponysay hello does the same thing as running nixsa/bin/nixsa ponysay hello.

We can add -v to see the command being run. If we run nixsa-dir/bin/nixsa -v ponysay hello, we see that Nixsa runs something like this:

NIX_USER_CONF_FILES=/home/noamraph/nixsa-dir/config/nix.conf \
NIX_CACHE_HOME=/home/noamraph/nixsa-dir/cache \
NIX_CONFIG_HOME=/home/noamraph/nixsa-dir/config \
NIX_DATA_HOME=/home/noamraph/nixsa-dir/share \
NIX_STATE_HOME=/home/noamraph/nixsa-dir/state \
bwrap \
  --bind /home/noamraph/nixsa-dir/nix /nix \
  --proc /proc \
  --dev /dev \
  --bind /home /home \
  ...
  bash -c 'source /home/noamraph/nixsa-dir/state/profile/etc/profile.d/nix.sh &&
           exec ponysay "$@"' \
  -- hello

This command:

1. Sets environment variables so Nix will use configuration and state files from the nixsa-dir folder.
2. Asks Bubblewrap to bind /nix in the environment to nixsa-dir/nix, and bind all other folders under / to the actual folders.
3. Runs a bash command which sources the nix.sh file in the active profile, and then executes the ponysay command with the argument hello.

In addition, after the command finishes, the nixsa executable looks at the current Nix profile, and updates the symlinks in the nixsa-dir/bin folder accordingly. For example, after running nixsa-dir/bin/nix install nixpkgs#ponysay, the symlink nixsa-dir/bin/ponysay will be created, linking to nixsa-dir/bin/nixsa.

In order to allow upgrades of the nixsa executable itself, nixsa-dir/bin/nixsa is a symlink to ../nix/store/HASH-nixsa-bin-VERSION/bin/nixsa. If you update the nixsa-bin package in the profile, Nixsa will update the nixsa-dir/bin/nixsa symlink accordingly.

Comparison to other tools

Nixsa is very similar in its purpose to nix-portable. The main differences that I see are:

• nix-portable doesn't support managing Nix profiles via nix-env or nix-profile, and doesn't support managing Nix channels via nix-channel. Nixsa does support those.
• nix-portable stores state and configuration in per-user directories, such as ~/.nix-portable. Nixsa keeps all state and configuration in the extracted directory, so you can have multiple Nixsa environments at once.
• Nixsa uses Bubblewrap to virtualize the /nix directory. nix-portable has multiple available runtimes to do this, Bubblewrap being one of them. It is probably possible to add more runtimes alternatives to Nixsa, if the need arises.

Another tool which allows using Nix without root is nix-user-chroot. It is a lower-level tool, which just runs a subprocess in an environment in which /nix is binded to another directory. So, in order to run a command installed by Nix, you either have to enter a shell by running nix-user-chroot ~/.nix bash -l, or create a script which calls nix-user-chroot in order to run the command.