guide about installing a Debian remotely with full disk encryption
This commit is contained in:
LUXEY Adrien
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README.md
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README.md
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Go to [deployer](deployer/), where the fun is at.
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## Structure
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* [`/deployer`](deployer/) contains deployment Ansible code for Serenity. **Being outdated** by migration to new server (HammerHead).
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* [`/bootstrapper`](bootstrapper/) contains Ansible configuration code for new servers (notably HammerHead). Will only take interest in the bootstrapping phase of the host. Service deployment will be handled by Nomad et al.
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## TODO
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* dockerise nextcloud, synapse, gitea
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* backup db
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* send backups to a remote
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* Host bootstrap Ansible code to [`/bootstrapper`](bootstrapper/)
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# Random notes
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# Bootstrap cluster hosts
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* `os_install/` contains documentation about OS installation for remote nodes
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* The rest is Ansible configuration
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## Configuration goals
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* Configure access rights
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User creation, upload their ssh keys, set passwordless sudo...
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* Installation of base toolset through package manager
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* Installation of complex tooling (e.g. Docker, Nomad, Vault, Consul) through other means (custom APT repo?)
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* Basic configuration of the server
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* Docker log rotation
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# Installing a cloud server with full disk encryption
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For hosting purposes, I am installing a new server on [Kimsufi](kimsufi.com/). This is a French public cloud provider (property of [OVH](ovh.com/)).
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It is well known that, at [Deuxfleurs](https://deuxfleurs.fr), we do not fancy hosting in datacenters: because of the lack on control on our machines, and potential privacy threats. In essence, people at Kimsufi could easily -- and without me knowing -- read my hard drive, and thus any sensitive user data stored inside.
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For that reason, I want to make it harder for their staff to access my data. A good first line of defense for that purpose is to encrypt the whole disk (*aka* Full Disk Encryption). Note that motivated attackers with physical access to my server would easily overcome the encryption. **If you really care about who accesses your data, keep your hard drives closest to you, e.g. at your home.**
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---
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Long story short: this guide presents a step-by-step installation of Debian buster on Kimsufi, using the [`dm-crypt`](https://wiki.archlinux.org/index.php/Dm-crypt) Linux kernel subsystem to encrypt the `/` and the `swap` partitions.
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Because I don't have physical access to the server, I need a way to *remotely enter the disk decryption password*, that is `dropbear` (a lightweight SSH server) inside `initramfs` (a minimal operating system that runs from RAM, before Linux boots).
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If you plan on doing the same without Kimsufi, know that it makes no difference: I am basically using a "rescue" console on another computer to configure `/dev/sda` (my server's system drive) for booting Linux with encrypted partitions.
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I must credit several useful guides that helped me succeed:
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* [OpsBlog guide on installing Linux with full-disk encryption and DropBear SSH on Kimsufi](https://opsblog.net/posts/full-disk-encrypted-ubuntu-kimsufi-sever/)
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DropBear allows SSH connection before boot, to remotely decrypt the main partition.
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* [Debian guide on installing Debian from a Linux system](https://www.debian.org/releases/wheezy/mipsel/apds03.html.en)
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## Overview of steps
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* Boot the Kimsufi server in rescue mode (gives you a remote shell with access to your system's hard drive).
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* Wipe filesystem, format partitions. I basically want:
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* A "cleartext" `/boot` partition
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* An encrypted `/` partition
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* An encrypted swap partition
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Docs on the encrypted swap:
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* [ArchLinux wiki: dm-crypt - Swap encryption](https://wiki.archlinux.org/index.php/Dm-crypt/Swap_encryption)
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* [cryptsetup FAQ](https://gitlab.com/cryptsetup/cryptsetup/-/wikis/FrequentlyAskedQuestions#2-setup): see "2.3 How do I set up encrypted swap?"
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* Install and configure Debian (including disk cryptography and decryption through SSH).
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* Boot and log into the server.
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* Setup automated decryption from a remote (in case of reboot).
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## Detailed process
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### Boot the server in rescue mode
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* Go to the Kimsufi admin panel, click "NetBoot", select "Rescue", pick "rescue64-pro", clock "Next", "Confirm", and then click the "Reboot" button on the admin panel.
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* Kimsufi will mail you the root password for you to log into the server in rescue mode.
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* Will likely cause an error from your SSH client, since the fingerprint of the server differs from the usual one.
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You should end up with a shell that has access to `/dev/sda`, your server's drive.
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### Wipe filesystem & format partitions
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Target partition table:
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```
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+-----------+--------------------+-----------+--------------------+
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Name: | /dev/sda1 | /dev/sda2 | /dev/sda3 | /dev/sda4 |
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| | | | |
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| | | | |
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| | +------------------+ | +------------------+
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| | | /dev/mapper/swap | | | /dev/mapper/main |
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Format: | none | | swap | ext4 | | ext4 |
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Size: | 1MiB | | 8GiB | 512MiB | | remaining space |
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Flags: | bios_grub | | | | | |
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Mount: | | | swap | /boot | | / |
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+-----------+-+------------------+-----------+-+------------------+
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```
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We use GPT partition table layout (without UEFI), which demands a small `bios_grub` partition at the beginning of the drive (stores GRUB's `core.img`). Hence `/dev/sda1`. See:
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* [Wikipedia: BIOS boot partition](https://en.wikipedia.org/wiki/BIOS_boot_partition)
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* [GNU: BIOS installation](https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html#BIOS-installation)
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* [ArchLinux wiki: Partitioning](https://wiki.archlinux.org/index.php/partitioning#Partition_table)
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* [Gentoo wiki: Installation - Disks](https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Disks#Partition_tables)
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* Wipe all information about previous filesystem:
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DANGER!!! DANGER!!! WIPES EVERYTHING FROM YOUR DISK!!!
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```bash
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wipefs -a /dev/sda
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```
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* Create GPT disk layout
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```bash
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# Create GPT layout
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parted -a optimal /dev/sda mklabel gpt
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# Create first 1MiB bios_grub partition
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parted /dev/sda -a optimal mkpart bios_grub 0% 1MiB
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parted /dev/sda set 1 bios_grub on
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# Create third 8GiB swap partition
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parted /dev/sda -a optimal mkpart swap 1MiB 8001MiB
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# Create second 512MiB /boot partition
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parted /dev/sda -a optimal mkpart boot 8001MiB 8513MiB
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# Create last / partition using all remaining space
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parted /dev/sda -a optimal mkpart main 8513MiB 100%
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# Set first partition as bootable
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```
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* Format partitions
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* The ext4 boot partition
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Format it like so:
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```bash
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mkfs.ext4 /dev/sda3
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```
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* The encrypted swap partition
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All configuration of the encrypted swap partition comes after the OS installation.
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* The encrypted main partition
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```bash
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# Set it up using cryptsetup (I searched for good parameters):
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cryptsetup --type luks2 --cipher aes-xts-plain64 --hash sha256 --iter-time 2000 --key-size 512 luksFormat /dev/sda4
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# Get the UUID, save it for later:
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cryptsetup luksDump /dev/sda4 | grep UUID | awk '{print $2}'
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# Example output: 09762476-ba7c-4732-8856-44a716c23339
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# Decrypt the partition:
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cryptsetup open /dev/sda4 main
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# Format it to ext4:
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mkfs.ext4 /dev/mapper/main
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```
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### Install and configure Debian
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* Mount the partitions
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```bash
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# Decrypt the main partition (if not already done):
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cryptsetup open /dev/sda4 main
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# mount it:
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mount /dev/mapper/main /mnt
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# Mount the boot partition:
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mkdir /mnt/boot
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mount /dev/sda3 /mnt/boot
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```
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* Bootstrap latest stable Debian into mounted partitions
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```bash
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debootstrap --arch amd64 stable /mnt http://ftp.fr.debian.org/debian/
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```
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* Mount system partitions
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```bash
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mount -o bind /dev /mnt/dev
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mount -t proc proc /mnt/proc
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mount -t sysfs sys /mnt/sys
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mount -t devpts devpts /mnt/dev/pts
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```
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* Chroot
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chroot /mnt /bin/bash
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* Fill out `crypttab` and `fstab` (`UUID` is the output of above `cryptsetup luksDump`)
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`/etc/crypttab`
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```bash
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cat << EOF > /etc/crypttab
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# <name> <device> <password> <options>
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main UUID=09762476-ba7c-4732-8856-44a716c23339 none luks
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swap /dev/sda2 /dev/urandom swap,noearly,cipher=aes-xts-plain64,size=512
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EOF
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```
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`/etc/fstab`
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```bash
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cat << EOF > /etc/fstab
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# <filesystem> <dir> <type> <options> <dump> <pass>
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/dev/mapper/main / ext4 errors=remount-ro 0 1
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/dev/sda3 /boot ext4 defaults 0 2
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/dev/mapper/swap none swap sw 0 0
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EOF
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```
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* Do the `/proc/mounts` -> `/etc/mtab` symlink
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```bash
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ln -s /proc/mounts /etc/mtab
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```
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Why? [Linux From Stratch](http://archive.linuxfromscratch.org/lfs-museum/3.3/LFS-BOOK-3.3-HTML/chapter06/mtablink.html) and [our guide on OpsBlog](https://opsblog.net/posts/full-disk-encrypted-ubuntu-kimsufi-sever/) both say it's needed.
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* Choose a hostname & DNS domain
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hammerhead & hammerhead.luxeylab.net
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* Fill in network-related files
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Beware of your ethernet interface name! It's only after failing with `eth0` that the boot logs informed me that the iface name was `eno1`.
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`/etc/network/interfaces`
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```bash
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cat << EOF > /etc/network/interfaces
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######################################################################
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# /etc/network/interfaces -- configuration file for ifup(8), ifdown(8)
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# See the interfaces(5) manpage for information on what options are
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# available.
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######################################################################
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# loopback interface
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auto lo
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iface lo inet loopback
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# eno1 through DHCP
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auto eno1
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iface eno1 inet dhcp
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EOF
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```
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`/etc/resolv.conf`
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```bash
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cat << EOF > /etc/resolv.conf
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# OVH public DNS
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nameserver 213.186.33.99
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# https://servers.opennicproject.org/edit.php?srv=ns2.he.de.dns.opennic.glue
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nameserver 172.104.136.243
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EOF
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```
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`/etc/hosts`
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```bash
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cat << EOF > /etc/hosts
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127.0.0.1 localhost
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127.0.1.1 hammerhead hammerhead.luxeylab.net
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# The following lines are desirable for IPv6 capable hosts
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::1 localhost ip6-localhost ip6-loopback
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fe00::0 ip6-localnet
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ff00::0 ip6-mcastprefix
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ff02::1 ip6-allnodes
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ff02::2 ip6-allrouters
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ff02::3 ip6-allhosts
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213.186.33.116 ws.ovh.com
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198.245.48.4 ws.ovh.ca
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5.135.179.11 hammerhead hammerhead.luxeylab.net
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EOF
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```
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`/etc/hostname`
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```bash
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echo "hammerhead" > /etc/hostname
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```
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`/etc/timezone`
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```bash
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dpkg-reconfigure tzdata
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```
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* Update APT repositories in `/etc/apt/sources.list`
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```bash
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cat << EOF > /etc/apt/sources.list
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deb http://ftp.fr.debian.org/debian buster main
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deb-src http://ftp.fr.debian.org/debian buster main
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deb http://ftp.fr.debian.org/debian-security/ buster/updates main
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deb-src http://ftp.fr.debian.org/debian-security/ buster/updates main
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deb http://ftp.fr.debian.org/debian buster-updates main
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deb-src http://ftp.fr.debian.org/debian buster-updates main
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EOF
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```
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* Configure locales & keyboard
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```bash
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# Refresh packages list
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apt update
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# Install & configure locales
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apt install locales && dpkg-reconfigure locales
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# Install & configure keyboard
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apt install console-setup console-data && dpkg-reconfigure keyboard-configuration
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```
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* Pick up a kernel & install it
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```bash
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apt-cache search linux-image
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# I selected the meta-package `linux-image-amd64` which is the latest
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apt install linux-image-amd64 linux-headers-amd64
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```
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* Install additional necessary software
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```bash
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apt install cryptsetup dropbear grub-pc man-db ssh
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```
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Because we use a GPT table layout but no UEFI, we install `grub-pc` and not `grub-efi-amd64`.
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Do think about installing `bash-completion` and `ufw` someday.
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* Set up SSH keys and the rest (where `<PUBLIC_SSH_KEY>` is your client SSH public key)
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```bash
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mkdir /root/.ssh && chmod 600 /root/.ssh
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echo "<PUBLIC_SSH_KEY>" > /root/.ssh/authorized_keys
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echo "<PUBLIC_SSH_KEY>" > /etc/dropbear-initramfs/authorized_keys
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```
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* Configure dropbear-initramfs (SSH on boot)
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```bash
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sed -i 's/#DROPBEAR_OPTIONS=/DROPBEAR_OPTIONS=\"-p 2222 -c \/bin\/cryptroot-unlock\"/' /etc/dropbear-initramfs/config
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```
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This changes the SSH listen post to 2222, and enforces that the only command run from `dropbear-initramfs` is `cryptroot-unlock`.
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* Configure sshd custom listen port (SSH after boot)
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```bash
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sed -i 's/#Port 22/Port 2223/' /etc/ssh/sshd_config
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```
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* [Optional] Authorize root password login
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```bash
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# Remove -s (disable password login) from dropbear-initramfs
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sed -i 's/local flags=\"Fs\"/local flags=\"F\"/' /usr/share/initramfs-tools/scripts/init-premount/dropbear
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```
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* Update GRUB and initramfs
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```bash
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update-grub && update-initramfs -u
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```
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* Clean up before leaving
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```bash
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exit
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umount /mnt/{boot,dev/pts,dev,proc,sys}
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umount /mnt
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cryptsetup luksClose main
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```
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### Boot and log into the server
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* I configured my laptop's `~/.ssh/config` like so:
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```
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Host hammerhead-decrypt
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User root
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Hostname <SERVER_URL_OR_IP>
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Port 2222
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IdentityFile <PRIVATE_SSH_KEY_PATH>
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# Prevents signatures mismatch
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UserKnownHostsFile ~/.ssh/known_hosts_hammerhead-decrypt
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Host hammerhead
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User root
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Hostname <SERVER_URL_OR_IP>
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Port 2223
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IdentityFile <PRIVATE_SSH_KEY_PATH>
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```
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* And here is how I connect to the server:
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```bash
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laptop$ ssh hammerhead-decrypt
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Please unlock disk main: <PASSWORD>
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# [...]
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Connection to <SERVER_URL_OR_IP> closed.
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laptop$ ssh hammerhead
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# [...]
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root@hamerhead:~# echo A winner is you!
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A winner is you!
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```
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### Setup automated decryption from a remote
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It is desirable to have a daemon running on a remote server, to automatically decrypt the drive when the encrypted server reboots without warning.
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The remote server is called a *key escrow*. One must be particularly careful about the escrow's security, since it holds the decryption keys for our server.
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Trinity recommends [Tang](https://github.com/latchset/tang) and [Clevis](https://github.com/latchset/clevis).
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