Install NixOS on OVH VPS

Backup your data.
Reboot into rescue mode with the control panel.
Connect to KVM with the control panel.

You can also SSH into the host with login credentials from KVM.

Download NixOS image.

Likely you won’t have enough disk space in rescue mode so use ramfs.

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mkdir /mnt/ramdisk
mount -t ramfs ramfs /mnt/ramdisk
cd /mnt/ramdisk
wget https://channels.nixos.org/nixos-21.11/latest-nixos-minimal-x86_64-linux.iso

Load image with qemu.

https://community.ovh.com/en/t/installing-operating-system-from-custom-image-on-ovh-vps-centos-8-tutorial/3561

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apt install qemu-kvm
qemu-system-x86_64 -netdev type=user,id=mynet0 -device virtio-net-pci,netdev=mynet0 -m 2048 -enable-kvm -drive index=0,media=disk,if=virtio,file=/dev/sdb -cdrom latest-nixos-minimal-x86_64-linux.iso -boot d

Connect to the installer inside QEMU guest.

On your local machine, forward the VNC port locally.
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ssh -o "UserKnownHostsFile=/dev/null" -NL 5900:localhost:5900 root@${YOUR_HOST}
Then connect to vnc://localhost with your VNC client. “Screen Sharing.app” on macOS somehow didn’t work for me.

Install as usual inside VNC.

Follow instructions in https://nixos.org/manual/nixos/stable/index.html#sec-installation. Use vda whenever sda is referenced.

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sudo -i
parted /dev/vda -- mklabel msdos
parted /dev/vda -- mkpart primary 1MiB -8GiB
parted /dev/vda -- mkpart primary linux-swap -8GiB 100%
mkfs.ext4 -L nixos /dev/sda1
mkswap -L swap /dev/sda2
mount /dev/disk/by-label/nixos /mnt
swapon /dev/vda2
nixos-generate-config --root /mnt
vi /mnt/etc/nixos/configuration.nix
# uncomment boot.loader.grub.device and set it to "/dev/vda"
nixos-install

Shutdown the qemu guest.
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shutdown -h now
Reboot with the control panel into non-rescue mode.
Now that we are no longer in rescue mode, change /dev/vda back to /dev/sda.
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vi /etc/nixos/configuration.nix
Done.

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