Testing and Entering NixOS Installations

1st chunk of `nixos/doc/manual/development/testing-installer.chapter.md`

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# Testing the Installer {#ch-testing-installer}

Building, burning, and booting from an installation CD is rather
tedious, so here is a quick way to see if the installer works properly:

```ShellSession
# mount -t tmpfs none /mnt
# nixos-generate-config --root /mnt
$ nix-build '<nixpkgs>' -A nixos-install
# ./result/bin/nixos-install
```

To start a login shell in the new NixOS installation in `/mnt`:

```ShellSession
$ nix-build '<nixpkgs>' -A nixos-enter
# ./result/bin/nixos-enter
```

Title: Testing and Entering NixOS Installations

Summary

This section provides a quick method to test the NixOS installer without the need for burning and booting from a CD. It outlines the shell commands required to mount a `tmpfs`, generate a configuration, build `nixos-install`, and execute it. Additionally, it details how to enter a login shell within a new NixOS installation by building and running `nixos-enter`.