Mic92 / Nixos Shell
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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
:
{ pkgs, ... }: {
boot.kernelPackages = pkgs.linuxPackages_latest;
}
How to install
nixos-shell
is available in nixpkgs unstable or in
NUR under
nur.repos.mic92.nixos-shell
.
Start a virtual machine
To start a vm use:
$ 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.
$ nixos-shell some-nix-module.nix
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:
$vm> poweroff
Or switch to qemu console with Ctrl-a c
and type:
(qemu) quit
Port forwarding
To forward ports from the virtual machine to the host, override the
virtualisation.qemu.networkingOptions
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.
If virtualisation.qemu.networkingOptions
is not overridden the same can be
also achieved by using the QEMU_NET_OPTS
environment variable.
$ 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
.
{ virtualisation.memorySize = "1024M"; }
CPUs
To increase the CPU count use virtualisation.cores
(defaults to 1):
{ virtualisation.cores = 2; }
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:
{ networking.firewall.enable = true; }
Mounting physical disks
There does not exists any explicit options right now but
one can use either the $QEMU_OPTS
environment variable
or set virtualisation.qemu.options
to pass the right qemu
command line flags:
{
# /dev/sdc also needs to be read-writable by the user executing nixos-shell
virtualisation.qemu.options = [ "-hdc" "/dev/sdc" ];
}
Boot with efi
{ virtualisation.qemu.options = [ "-bios" "${pkgs.OVMF.fd}/FV/OVMF.fd" ]; }
Shared folders
To mount anywhere inside the virtual machine, use the nixos-shell.mounts.extraMounts
option.
{
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:
{
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.
In older version one can set the virtualisation.qemu.options
or set the environment variable QEMU_OPTS
:
export QEMU_OPTS="-cpu max"
nixos-shell
A full list of supported qemu cpus can be obtained by running qemu-kvm -cpu help
.
More configuration
Have a look at the virtualisation options NixOS provides.