Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/Mic92/nixos-shell

Spawns lightweight nixos vms in a shell
https://github.com/Mic92/nixos-shell

managed-by-renovate

Last synced: about 2 months ago
JSON representation

Spawns lightweight nixos vms in a shell

Awesome Lists containing this project

README 

        
# nixos-shell



* Spawns a headless qemu virtual machines based on a `vm.nix` nixos module in the current working directory.

* Mounts `$HOME` and the user's nix profile into the virtual machine

* Provides console access in the same terminal window



Example `vm.nix`:



```nix

{ pkgs, ... }: {

  boot.kernelPackages = pkgs.linuxPackages_latest;

}

```



## How to install



`nixos-shell` is available in nixpkgs.



## Start a virtual machine



To start a vm use:



```console

$ nixos-shell

```



In this case `nixos-shell` will read `vm.nix` in the current directory.

Instead of `vm.nix`, `nixos-shell` also accepts other modules on the command line.



```console

$ nixos-shell some-nix-module.nix

```



You can also start a vm from a flake's `nixosConfigurations` or `nixosModules` output using the `--flake` flag.



```console

$ nixos-shell --flake github:Mic92/nixos-shell#vm-forward

```



This will run the `vm-forward` example.



> Note: `nixos-shell` must be able to extend the specified system configuration with [certain modules](share/modules).

>

> If your version of `nixpkgs` provides the `extendModules` function on system configurations, `nixos-shell` will use it to inject the required modules; no additional work on your part is needed.

>

> If your version of `nixpkgs` **does not** provide `extendModules`, you must make your system configurations overridable with `lib.makeOverridable` to use them with `nixos-shell`:

>```nix

>{

>  nixosConfigurations = let

>    lib = nixpkgs.lib;

>  in {

>    vm = lib.makeOverridable lib.nixosSystem {

>      # ...

>    };

>  };

>}

>```

> Specifying a non-overridable system configuration will cause `nixos-shell` to abort with a non-zero exit status.



When using the `--flake` flag, if no attribute is given, `nixos-shell` tries the following flake output attributes:

- `packages..nixosConfigurations.`

- `nixosConfigurations.`

- `nixosModules.`



If an attribute _name_ is given, `nixos-shell` tries the following flake output attributes:

- `packages..nixosConfigurations.`

- `nixosConfigurations.`

- `nixosModules.`



## Terminating the virtual machine



Type `Ctrl-a x` to exit the virtual machine.



You can also run the `poweroff` command in the virtual machine console:



```console

$vm> poweroff

```



Or switch to qemu console with `Ctrl-a c` and type:



```console

(qemu) quit

```



## Port forwarding



To forward ports from the virtual machine to the host, use the

`virtualisation.forwardPorts` NixOS option.

See `examples/vm-forward.nix` where the ssh server running on port 22 in the

virtual machine is made accessible through port 2222 on the host.



The same can be also achieved by using the `QEMU_NET_OPTS` environment variable.



```console

$ QEMU_NET_OPTS="hostfwd=tcp::2222-:22" nixos-shell

```



### SSH login



Your keys are used to enable passwordless login for the root user.

At the moment only `~/.ssh/id_rsa.pub`, `~/.ssh/id_ecdsa.pub` and `~/.ssh/id_ed25519.pub` are

added automatically. Use `users.users.root.openssh.authorizedKeys.keyFiles` to add more.



*Note: sshd is not started by default. It can be enabled by setting

`services.openssh.enable = true`.*



## Bridge Network



QEMU is started with user mode network by default. To use bridge network instead, 

set `virtualisation.qemu.networkingOptions` to something like

`[ "-nic bridge,br=br0,model=virtio-net-pci,mac=11:11:11:11:11:11,helper=/run/wrappers/bin/qemu-bridge-helper" ]`. `/run/wrappers/bin/qemu-bridge-helper` is a NixOS specific

path for qemu-bridge-helper on other Linux distributions it will be different.

QEMU needs to be installed on the host to get `qemu-bridge-helper` with setuid bit 

set - otherwise you will need to start VM as root. On NixOS this can be achieved using

`virtualisation.libvirtd.enable = true;`



## RAM



By default qemu will allow at most 500MB of RAM, this can be increased using `virtualisation.memorySize` (size in megabyte).



```nix

{ virtualisation.memorySize = 1024; }

```



## CPUs



To increase the CPU count use `virtualisation.cores` (defaults to 1):



```nix

{ virtualisation.cores = 2; }

```



## Hard drive



To increase the size of the virtual hard drive, i. e. to 20 GB (see [virtualisation] options at bottom, defaults to 512M):



```nix

{ virtualisation.diskSize = 20 * 1024; }

```



Notice that for this option to become effective you may also need to delete previous block device files created by qemu (`nixos.qcow2`).



Notice that changes in the nix store are written to an overlayfs backed by tmpfs rather than the block device

that is configured by `virtualisation.diskSize`. This tmpfs can be disabled however by using:



```nix

{ virtualisation.writableStoreUseTmpfs = false; }

```



This option is recommend if you plan to use nixos-shell as a remote builder.



## Graphics/Xserver



To use graphical applications, add the `virtualisation.graphics` NixOS option (see `examples/vm-graphics.nix`).



## Firewall



By default for user's convenience `nixos-shell` does not enable a firewall.

This can be overridden by:



```nix

{ networking.firewall.enable = true; }

```



## Mounting physical disks



There does not exists any explicit options right now but 

one can use either the `$QEMU_OPTS` environment variable

or set `virtualisation.qemu.options` to pass the right qemu

command line flags:



```nix

{

  # /dev/sdc also needs to be read-writable by the user executing nixos-shell

  virtualisation.qemu.options = [ "-hdc" "/dev/sdc" ];

}

```



## Boot with efi



``` nix

{ virtualisation.qemu.options = [ "-bios" "${pkgs.OVMF.fd}/FV/OVMF.fd" ]; }

```



## Shared folders



To mount anywhere inside the virtual machine, use the `nixos-shell.mounts.extraMounts` option.



```nix

{

  nixos-shell.mounts.extraMounts = {

    # simple USB stick sharing

    "/media" = /media;



    # override options for each mount

    "/var/www" = {

      target = ./src;

      cache = "none";

    };

  };

}

```



You can further configure the default mount settings:



```nix

{

  nixos-shell.mounts = {

    mountHome = false;

    mountNixProfile = false;

    cache = "none"; # default is "loose"

  };

}

```



Available cache modes are documented in the [9p kernel module].



## Disable KVM



In many cloud environments KVM is not available and therefore nixos-shell will fail with:  

`CPU model 'host' requires KVM`.  

In newer versions of nixpkgs this has been fixed by falling back to [emulation](https://github.com/NixOS/nixpkgs/pull/95956).

In older version one can set the `virtualisation.qemu.options` or set the environment variable `QEMU_OPTS`:



```bash

export QEMU_OPTS="-cpu max"

nixos-shell

```



A full list of supported qemu cpus can be obtained by running `qemu-kvm -cpu help`.



## Channels/NIX_PATH



By default VMs will have a NIX_PATH configured for nix channels but no channel are downloaded yet.

To avoid having to download a nix-channel every time the VM is reset, you can use the following nixos configuration:



```nix

{...}: {

  nix.nixPath = [

    "nixpkgs=${pkgs.path}"

  ];

}

```



This will add the nixpkgs that is used for the VM in the NIX_PATH of login shell.



## Embedding nixos-shell in your own nixos-configuration



Instead of using the cli, it's also possible to include the `nixos-shell` NixOS module in your own NixOS configuration.



Add this to your `flake.nix`:



```nix

{

  inputs.nixos-shell.url = "github:Mic92/nixos-shell";

}

```



And this to your nixos configuration defined in your flake:



```nix

{

  imports = [ inputs.nixos-shell.nixosModules.nixos-shell ];

}

```



Afterwards you can start your nixos configuration with nixos-shell with one of the two following variants:



For the pure version (doesn't set SHELL or mount /home):



```

nix run .#nixosConfigurations..config.system.build.nixos-shell

```



Or for a version closer to `nixos-shell`:



```

nix run .#nixosConfigurations..config.system.build.nixos-shell

```



## More configuration



Have a look at the [virtualisation] options NixOS provides.



[virtualisation]: https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/qemu-vm.nix

[9p kernel module]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Documentation/filesystems/9p.rst