Installing Arch Linux with Full Disk Encryption

2020-07-29 #privacy #linux

Updates

• 2022-12-17: The official archinstall script greatly simplify the Arch Linux installation, even with full disk encryption. Most steps in this guide (except 18 unlock automatically) are automated by that script. Check it out!

I recently re-installed my Arch Linux with full disk encryption (FDE), as one of the first steps, to bring privacy into my life. This guide documents the installation process in a step-by-step manner. I hope this can help people who also want to practice privacy.

Each step in this guide are linked to the corresponding ArchWiki, precised to section level. You are suggested to read these references and, of course, the official installation guide because

• it is better to understand the process instead of blindly copy-and-pase, and
• I had omitted some uncommon steps that you might need (e.g., non US locale and keyboard layout)

This guide uses modern options like:

In addition, I have verified this guide twice by installing on both hard disk and virtual machine respectively. I think it is reproducible.

Let’s start!

1. Verify the boot mode (ref)

This guide assumes we use UEFI. You must ensure that the system is booted in UEFI mode. To verify the boot mode, list the efivars directory:

# ls /sys/firmware/efi/efivars

If the command shows the directory without error, then the system is booted in UEFI mode.

2. Update the system clock (ref)

Use timedatectl to ensure the system clock is accurate:

# timedatectl set-ntp true

3. Partition the disks (ref, GPT fdisk)

The final disk layout from this guide contains two partitions,

Traditionally, it is suggested to create an extra swap partition. I don’t because there are more flexible alternatives over allocating a fixed partition for swap. For example, uses swap file, or systemd-swap to automate the swap file on demand.

Use gdisk to partition the disk. See this video.

When completed, gdisk -l /dev/sda should print the disk partitions like these:

GPT fdisk (gdisk) version 1.0.5

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 41943040 sectors, 20.0 GiB
Model: VBOX HARDDISK
Sector size (logical/physical): 512/512 bytes
Disk identifier (GUID): 8EFD04A2-473C-4FCA-9C89-459EEB658DB0
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 41943006
Partitions will be aligned on 2048-sector boundaries
Total free space is 2014 sectors (1007.0 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048         1050623   512.0 MiB   EF00  EFI system partition
   2         1050624        41943006    19.5 GiB   8300  Linux filesystem

4. Prepare the encrypted root partition (ref)

Create and mount the encrypted root partition. You will need to choose the passphrase for the encryption!

# cryptsetup luksFormat /dev/sda2
# cryptsetup open /dev/sda2 cryptroot
# mkfs.ext4 /dev/mapper/cryptroot
# mount /dev/mapper/cryptroot /mnt

5. Prepare the boot partition (ref)

Create and mount the non-encrypted boot partition.

# mkfs.fat -F32 /dev/sda1
# mkdir /mnt/boot
# mount /dev/sda1 /mnt/boot

6. Generate an fstab file (ref)

Run:

# genfstab -U /mnt >> /mnt/etc/fstab

7. Install essential packages (ref)

Use the pacstrap script to install these packages. I added vim for editing config files and dhcpcd for connecting to the Internet after reboot.

# pacstrap /mnt base linux linux-firmware vim dhcpcd

8. Chroot (ref)

# arch-chroot /mnt

9. Time zone (ref)

# ln -sf /usr/share/zoneinfo/America/Los_Angeles /etc/localtime
# hwclock --systohc

10. Localization (ref)

Edit /etc/locale.gen and uncomment en_US.UTF-8 UTF-8 and other needed locales. Generate the locales by running:

# locale-gen
# localectl set-locale LANG=en_US.UTF-8

11. Network configuration (ref)

Add the /etc/hosts:

127.0.0.1  localhost
::1        localhost

12. Configuring mkinitcpio (ref)

Edit /etc/mkinitcpio.conf, - add the encrypt hooks - move the keyboard hooks before encrypt ( so that you can type the passphrase :p )

For example, after this step, HOOKS should look like:

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

13. Generate the initramfs (ref)

Since we have changed to /etc/mkinitcpio.conf manually, we have to re-generates the boot images (e.g., /boot/initramfs-linux.img). Run this command:

# mkinitcpio -P

14. Set the root password (ref)

# passwd

15. Patch the CPU’s microcode (ref)

• For AMD processors, install the amd-ucode package.
• For Intel processors, install the intel-ucode package.

For exmaple, run

# pacman -S intel-ucode

16. Configure the Boot Loader with systemd-boot (ref, systemd-boot)

16.1. Install the EFI boot manager

# bootctl install

16.2. Create /boot/loader/entries/arch.conf

• Replace intel-ucode.img with amd-ucode.img if you have an AMD CPU
• Replace the UUID (not PARTUUID) to the one mapping to /dev/sda2 (Run blkid to find out)

title   Arch Linux
linux   /vmlinuz-linux
initrd  /intel-ucode.img
initrd  /initramfs-linux.img
options cryptdevice=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX:cryptroot root=/dev/mapper/cryptroot rw

16.3. Replace /boot/loader/loader.conf to

default      arch.conf
timeout      5
console-mode max
editor       no

16.4. Review the configuration

# bootctl list
Boot Loader Entries:
        title: Arch Linux (default)
           id: arch.conf
       source: /boot/loader/entries/arch.conf
        linux: /vmlinuz-linux
       initrd: /intel-ucode.img
               /initramfs-linux.img
      options: cryptdevice=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX:cryptroot root=/dev/mapper/cryptroot rw

17. Reboot (ref)

Exit the chroot environment by typing exit or pressing Ctrl+d. Then run reboot.

If everything works, it should ask for a password to access the cryptroot, like this screenshot below:

One last thing, if you computer, like mine, is sitting behind a DHCP (e.g., a typical router), you will need to enable dhcpcd to access the Internet. Run,

# systemctl enable dhcpcd

Congratulations! You have installed Arch Linux with Full Disk Encryption!

18. (Optional) Unlocking the Root Partition at boot (ref)

The above setup requires manual interruption on each reboot by entering the password to unlock the disk. There are ways to avoid at the expense of reducing the security level because the decryption key is exposed.

The one I use is to include the decryption key to the _{initram-fs.img} so that the systemd module encrypt can use it to decrypt the root partition automatically.

Steps:

1. adds a key file to /crypto_keyfile.bin, the default location read by the encrypt module used above.
2. adds the /crypto_keyfile.bin to FILES=() array in /etc/mkinitcpio.conf, so that this file is copied to the image (e.g., _{initram-fs.img}).
3. regenerates the images with mkinitcpio -P.