Arch Linux with LUKS and btrfs on a Hetzner server

Software

This guide shows how to set up the following software composition:

• Arch Linux
• btrfs
• LUKS

Requirements

Written for a Dedicated Hetzner server with the following hardware specifications:

CPU1: Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz (Cores 8)
Memory:  15973 MB
Disk /dev/sda: 3000 GB (=> 2794 GiB)
Disk /dev/sdb: 3000 GB (=> 2794 GiB)
Total capacity 5589 GiB with 2 Disks

Legend

The following symbols show in which environment the code is executed:

• 💻 Client
• 🚑 Hetzner Rescue System
• 👻 Chroot from Rescue System into Arch
• 💽 Arch OS

CLI helper (hal)

This repo ships a small Python CLI (hal) that wraps the recurring SSH / LUKS / chroot dances. Install it once on your client:

pip install --user -e .

After that, hal is on your $PATH. Subcommands used throughout the guide:

Command	What it does
hal status <host>	Probe reachability (ping, ports 22/222, SSH banner). No login.
hal connect rescue <host>	Wait for rescue, drop known_hosts entry, SSH in as root.
hal connect chroot <host>	Prompt LUKS passphrase first (hidden), then via rescue: assemble RAID → unlock LUKS → mount → drop into chroot /mnt /bin/bash.
hal diagnose <host>	Same setup as connect chroot, then runs a fixed diagnostic script inside the chroot and prints the report to stdout.

The passphrase prompt happens before the SSH connection is established, so you can type it once, walk away, and the rest runs unattended.

Guide

1. Configure and Install Image

1.1 Login to Hetzner Rescue System

💻 :

hal connect rescue your_server_ip

1.2 Create the /autosetup

🚑 :

nano /autosetup

Save the following content into this file:

##  Hetzner Online GmbH - installimage - config

DRIVE1 /dev/sda
DRIVE2 /dev/sdb

##  SOFTWARE RAID:
## activate software RAID?  < 0 | 1 >
SWRAID 1

## Choose the level for the software RAID < 0 | 1 | 10 >
SWRAIDLEVEL 1

##  BOOTLOADER:
BOOTLOADER grub

##  HOSTNAME:
HOSTNAME hetzner-arch-luks
#Adapt the hostname to your needs

##  PARTITIONS / FILESYSTEMS:
PART /boot  btrfs     512M
PART lvm    vg0       all
LV vg0   swap   swap     swap         8G
LV vg0   root   /        btrfs        10G

##  OPERATING SYSTEM IMAGE:
IMAGE /root/.oldroot/nfs/install/../images/archlinux-latest-64-minimal.tar.gz

1.3 Install Image

🚑 :

installimage

1.4 Restart

🚑 :

reboot

2. Setup System

2.1 Login to server

💻 :

ssh-keygen -f "$HOME/.ssh/known_hosts" -R your_server_ip
ssh root@your_server_ip

2.2 Update the system

💽 :

pacman -Syyu

2.3 Install administration tools:

💽 :

pacman -S nano

3. Prepare System for Unlocking via SSH

3.1 Install software

💽 :

pacman -S busybox mkinitcpio-dropbear mkinitcpio-utils mkinitcpio-netconf

3.2 Copy authorized keys to dropbear

💽 :

cp -v ~/.ssh/authorized_keys /etc/dropbear/root_key

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
systemctl enable sshd

3.3 Regenerate OpenSSH keys

💽 :

rm /etc/ssh/ssh_host_*
ssh-keygen -A -m PEM

3.4 Import SSH-keys to dropbear

💽 :

dropbearconvert openssh dropbear /etc/ssh/ssh_host_rsa_key /etc/dropbear/dropbear_rsa_host_key

3.5 Modify /etc/mkinitcpio.conf

💽 :

nano /etc/mkinitcpio.conf

Replace

Old:

HOOKS=(base udev autodetect modconf block mdadm_udev lvm2 filesystems keyboard fsck)

New:

HOOKS=(base udev autodetect modconf block mdadm_udev lvm2 netconf dropbear encryptssh filesystems keyboard fsck)

4. Activate Encryption

4.1 Activate Rescue System

Activate the rescue system https://robot.your-server.de/server

4.2 Reboot

💽 :

reboot

4.3 Login to the rescue system

💻 :

hal connect rescue your_server_ip

4.4 Mount the "system"

🚑 :

vgscan -v
vgchange -a y
mount /dev/mapper/vg0-root /mnt

4.5 Copy "system"

🚑 :

echo 0 >/proc/sys/dev/raid/speed_limit_max
mkdir /oldroot
cp -va /mnt/. /oldroot/.
echo 200000 >/proc/sys/dev/raid/speed_limit_max

4.6 Unmount the "system"

🚑 :

umount /mnt

4.7 Delete decrypted LVM-Volume-Group

🚑 :

vgremove vg0

4.8 Check drive state

🚑 :

cat /proc/mdstat

4.9 Encrypt MD1 by executing

🚑 :

cryptsetup --cipher aes-xts-plain64 --key-size 256 --hash sha256 --iter-time=10000 luksFormat /dev/md1
cryptsetup luksOpen /dev/md1 cryptroot
pvcreate /dev/mapper/cryptroot
vgcreate vg0 /dev/mapper/cryptroot
lvcreate -n swap -L8G vg0
lvcreate -n root -L10G vg0
mkfs.btrfs /dev/vg0/root
mkswap /dev/vg0/swap

4.10 Mount encrypted

🚑 :

mount /dev/vg0/root /mnt

4.12 Copy "system"

🚑 :

echo 0 >/proc/sys/dev/raid/speed_limit_max
cp -av /oldroot/. /mnt/.
echo 200000 >/proc/sys/dev/raid/speed_limit_max

4.13 Integrate Finale Installation

🚑 :

mount /dev/md0 /mnt/boot
mount --bind /dev /mnt/dev
mount --bind /sys /mnt/sys
mount --bind /proc /mnt/proc
chroot /mnt

4.14

👻 :

echo "cryptroot /dev/md1 none luks" >> /etc/crypttab

4.15 Create an initial ramdisk

👻 :

mkinitcpio -p linux

5 Grub

5.1 Install Grub

👻 :

pacman -S grub

5.2 Configure /etc/default/grub

👻 :

nano /etc/default/grub

Change the following parameters:

GRUB_CMDLINE_LINUX="cryptdevice=/dev/md1:cryptroot ip=dhcp"
GRUB_ENABLE_CRYPTODISK=y

ℹ️ Further information.

5.3 Make and Install on Hard-drives

👻 :

grub-mkconfig -o /boot/grub/grub.cfg
grub-install /dev/sda
grub-install /dev/sdb

5.4 Restart System

👻 🚑 :

exit
umount /mnt/boot /mnt/proc /mnt/sys /mnt/dev
umount /mnt
sync
reboot

6. Encryption Procedure

6.1 Decrypt server

💻 :

ssh  -o UserKnownHostsFile=/dev/null root@your_server_ip
cryptroot-unlock
exit

6.2 Login to server

💻 :

ssh-keygen -f "$HOME/.ssh/known_hosts" -R your_server_ip
ssh root@your_server_ip

7. Expand filesystem

💻 :

lvresize -l +100%FREE /dev/vg0/root
btrfs filesystem resize max /

8. Debugging

8.1 Login to System from Rescue System

With the rescue system already activated and running, drop straight into the chroot from your client:

💻 :

hal connect chroot your_server_ip

You'll be prompted for the LUKS passphrase first (hidden input). The CLI then waits for rescue, assembles the RAID, opens LUKS, activates LVM, mounts /mnt + /mnt/boot + the pseudo-filesystems, and drops you into chroot /mnt /bin/bash. Idempotent — re-running while already mounted just re-enters the chroot.

8.2 Collect diagnostics in one shot

If you want a non-interactive snapshot of the installed system's state (package versions, last-boot journal errors, sshd status, /boot contents, etc.):

💻 :

hal diagnose your_server_ip | tee "diagnose-$(date +%F-%H%M).log"

The CLI runs the same setup as connect chroot and then a fixed inspection script inside the chroot. Output goes to stdout (and the log file via tee).

Manual equivalent of the unlock + mount sequence

🚑 :

cryptsetup luksOpen /dev/md1 cryptroot
mount /dev/vg0/root /mnt
mount /dev/md0 /mnt/boot
mount --bind /dev /mnt/dev
mount --bind /sys /mnt/sys
mount --bind /proc /mnt/proc
chroot /mnt

### 8.3 Logout from chroot environment 👻 🚑 : ```bash exit umount /mnt/boot /mnt/proc /mnt/sys /mnt/dev umount /mnt sync reboot ```

8.4 Regenerate GRUB and Arch

👻 :

mkinitcpio -p linux
grub-mkconfig -o /boot/grub/grub.cfg
grub-install /dev/sda
grub-install /dev/sdb

Sources

The code is adapted from the following guides:

• http://daemons-point.com/blog/2019/10/20/hetzner-verschluesselt/
• https://www.howtoforge.com/using-the-btrfs-filesystem-with-raid1-with-ubuntu-12.10-on-a-hetzner-server
• https://code.trafficking.agency/arch-linux-remote-unlock-root-volume-with-mdraid-and-dmcrypt.html
• https://wiki.archlinux.org/index.php/Dm-crypt/Specialties#Remote_unlocking_(hooks:_netconf,_dropbear,_tinyssh,_ppp)
• https://gist.github.com/pezz/5310082