146 lines
6.3 KiB
Markdown
146 lines
6.3 KiB
Markdown
# nixos
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## Installation
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Follow the [NixOS manual](https://nixos.org/manual/nixos/stable/index.html#ch-installation) to obtain and boot
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the installation medium. Use the graphical ISO image since it ships with useful programs such as `nmtui`; the
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installation can still be done through the terminal.
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### Disk Partitioning
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For [impermanence](https://nixos.wiki/wiki/Impermanence), partitioning should be done as outlined in the [tmpfs
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as root](https://elis.nu/blog/2020/05/nixos-tmpfs-as-root/) blogpost, but with `/nix` as a [LUKS-encrypted file
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system](https://nixos.org/manual/nixos/stable/index.html#sec-luks-file-systems). The boot partition will not be
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encrypted, since that is poorly supported by systemd-boot. Persistent files will be saved under `/nix/persist`. To
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find out which of our darlings will be erased on reboot do `tree -x /` or `ncdu -x /`.
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The following is based on the [tmpfs as root](https://elis.nu/blog/2020/05/nixos-tmpfs-as-root/) blogpost, the NixOS
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manual's [partitioning](https://nixos.org/manual/nixos/stable/index.html#sec-installation-manual-partitioning),
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[formatting](https://nixos.orgmanual/nixos/stable/index.html#sec-installation-manual-partitioning-formatting) and
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[LUKS-Encrypted File Systems](https://nixos.org/manual/nixos/stable/index.html#sec-luks-file-systems) sections,
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ArchWiki's [LVM on LUKS](https://wiki.archlinux.org/title/Dm-crypt/Encrypting_an_entire_system#LVM_on_LUKS),
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the unofficial NixOS wiki [Full Disk Encryption](https://nixos.wiki/wiki/Full_Disk_Encryption), and [this GitHub
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gist](https://gist.github.com/martijnvermaat/76f2e24d0239470dd71050358b4d5134).
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We create a 1GiB EFI boot partition (`/dev/sda1`) and the rest will be our LUKS-encrypted volume:
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```fish
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# Create partition table
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parted /dev/sda -- mklabel gpt
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# Create /boot partition
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parted /dev/sda -- mkpart ESP fat32 1MiB 1024MiB
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parted /dev/sda -- set 1 esp on
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# Create /nix partition
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parted /dev/sda -- mkpart primary 1024MiB 100%
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# Create and open LUKS-encrypted container
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cryptsetup --type=luks2 luksFormat --label=crypted /dev/sda2
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cryptsetup open /dev/sda2 crypted
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# Create LVM volume group
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pvcreate /dev/mapper/crypted
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vgcreate vg /dev/mapper/crypted
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# Create root logical volume
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lvcreate -l 100%FREE vg -n root
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# Format partitions
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mkfs.fat -F32 -n BOOT /dev/sda1
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mkfs.ext4 -L nix /dev/vg/root
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```
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The result should be the following (`lsblk -f`):
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```text
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NAME FSTYPE FSVER LABEL
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sda
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├─sda1 vfat FAT32 BOOT
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└─sda2 crypto_LUKS 2 crypted
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└─crypted LVM2_member LVM2 001
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└─vg-root ext4 1.0 nix
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```
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Whereas the [NixOS manual](https://nixos.org/manual/nixos/stable/index.html#sec-installation-manual-installing) mounts
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the newly-created `nixos` partition to `/mnt`, we will follow the _tmpfs as root_ blogpost and mount `/mnt` as `tmpfs`:
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```fish
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mount -t tmpfs none /mnt
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mount --mkdir /dev/disk/by-label/BOOT /mnt/boot
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mount --mkdir /dev/disk/by-label/nix /mnt/nix
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mkdir -p /mnt/nix/persist/
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```
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### Secrets
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All files in the Nix store are world-readable, so it is not a suitable place for including cleartext secrets,
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even if we had a scheme to securely transfer them to each system. [Agenix](https://github.com/ryantm/agenix)
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solves this issue by encrypting the secrets using [age](https://github.com/FiloSottile/age), and then decrypting
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and symlinking them using the system's SSH host key during system activation.
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All secrets, and other private configuration such as DNS zonefiles, are stored
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in a separate, private [repo](https://git.caspervk.net/caspervk/nixos-secrets).
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To bootstrap a new system, we must first generate a host key manually using
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`ssh-keygen -A -f /mnt/nix/persist` during installation. Then, on an existing
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system, add the new host's public key to `secrets.nix` in the `nixos-secrets`
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repo and rekey all secrets using `agenix --rekey`. Commit and transfer the
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repository to the new system.
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When managing secrets, the Keepass recovery key is used like so:
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```fish
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set AGE_KEY_FILE (mktemp); read -s > $AGE_KEY_FILE
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agenix -i $AGE_KEY_FILE -e foo.age
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```
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### Installation
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The remaining installation can be done (more or less) according to the [NixOS
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manual](https://nixos.org/manual/nixos/stable/index.html#sec-installation-manual-installing).
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```fish
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cd /mnt/nix
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git clone https://git.caspervk.net/caspervk/nixos.git tmp
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cd tmp/
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nixos-generate-config --root /mnt --show-hardware-config
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vim hosts/omega/hardware.nix
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git add . # nix sometimes ignores files outside version control
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nixos-install --no-root-passwd --flake .#omega --override-input secrets ./../nixos-secrets/
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```
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### Hardware Configuration
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`hosts/*/hardware.nix`, while initially generated by `nixos-generate-config --show-hardware-config`, _is_ manually
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modified.
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### State Version
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Nixpkgs uses `stateVersion` so sparingly that auditing the entire nixpkgs repo is [easy
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enough](https://sourcegraph.com/search?q=context%3Aglobal+repo%3A%5Egithub%5C.com%3FNixOS%2Fnixpkgs%24++lang%3ANix+stateVersion+AND+23.11).
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## Useful Commands
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```fish
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# development
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sudo nixos-rebuild switch --flake . --override-input secrets ./../nixos-secrets/
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# start build environment with user's default shell instead of bash
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nix develop --command $SHELL
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# nix shell with python packages
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# https://discourse.nixos.org/t/nix-shell-for-python-packages/16575
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# https://github.com/NixOS/nix/issues/5567
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nix shell --impure --expr 'with builtins.getFlake "nixpkgs"; with legacyPackages.${builtins.currentSystem}; python3.withPackages (ps: with ps; [ numpy ])'
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```
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### Debugging
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```nix
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# load flake into repl
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nix repl . --override-input secrets ./../nixos-secrets/
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# print a configuration option
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:p nixosConfigurations.omega.options.services.openssh.ports.declarationPositions # declaration
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:p nixosConfigurations.omega.options.services.openssh.ports.default # declaration default
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:p nixosConfigurations.omega.options.services.openssh.ports.definitionsWithLocations # overwrites
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:p nixosConfigurations.omega.options.services.openssh.ports.value # current value
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# print derivation package names
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:p builtins.map (d: d.name) outputs.nixosConfigurations.omega.options.environment.systemPackages.value
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# print version of package in nixpkgs
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:p inputs.nixpkgs.outputs.legacyPackages.${builtins.currentSystem}.openssh.version
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```
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## References
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- https://github.com/nix-community/srvos/tree/29a48ae201fbd69b6b71acdae5e19fa2ceaa8181
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