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Installing Arch Linux with Btrfs, systemd-boot and LUKS

My preferred Arch Linux setup is with Btrfs, systemd-boot (which requires UEFI) and - at least when installing a laptop - LUKS. Not least to make the next installation easier for myself, I thought it would be a good idea to document the steps.

Note

This post describes the creation and usage of a swap file, but that's optional.

Using SSH

If you have another PC, it's convenient to do the installation from this PC via SSH because then you can have browser windows with installation guides open in parallel and easily copy and paste commands. To do so, boot the PC that you want to install from the Arch Linux ISO. The SSH daemon is already running on the ISO.

Set a password for root:

passwd

Look up the IP address of the PC:

ip addr

Now, on the second PC, connect to the first PC via SSH:

ssh root@<IP-OF-THE-FIRST-PC>

and continue with the installation.

Partitioning

Note

For the rest of this post, we assume that we install Arch Linux on an SSD with the device path /dev/nvme0n1.

Adjust the steps for your setup if necessary.

gdisk /dev/nvme0n1

Create a new partition table:

Command (? for help): o

Create an EFI partition (choose size 1G and hex code EF00):

Command (? for help): n

Create a root partition (accept the default values):

Command (? for help): n

Write the new partitions to disk:

Command (? for help): w

Encryption

Create an encrypted container for the root file system (you need to define a passphrase):

cryptsetup luksFormat /dev/nvme0n1p2

Open the container ("root" is just a placeholder; you can use a name of your choice, but remember to adapt the subsequent steps of the guide accordingly):

cryptsetup open /dev/nvme0n1p2 root

Create file systems

Format the EFI partition with FAT32 and give it the label EFI - you can choose any other label name:

mkfs.vfat -F32 -n EFI /dev/nvme0n1p1

Format the root partition with Btrfs and give it the label SYSTEM - you can choose any other label name. If you didn't open the LUKS container under the name "root", you must adjust the command accordingly:

mkfs.btrfs -L SYSTEM /dev/mapper/root

Create and mount subvolumes

Note

If you don't want to use a swap file, it is not required to create and mount the subvolume @swap.

Create subvolumes for root, home, cache, log, tmp, and snapshots (cache, log and tmp get separate subvolumes since I want to be able to create snapshots of root without all the temporary and cached data of /var/cache, /var/log and /var/tmp):

mount /dev/mapper/root /mnt
btrfs sub create /mnt/@
btrfs sub create /mnt/@home
btrfs sub create /mnt/@cache
btrfs sub create /mnt/@log
btrfs sub create /mnt/@tmp
btrfs sub create /mnt/@snapshots
btrfs sub create /mnt/@swap
umount /mnt

Mount the subvolumes:

mount --mkdir -o noatime,compress=zstd,subvol=@ /dev/mapper/root /mnt
mount --mkdir -o noatime,compress=zstd,subvol=@home /dev/mapper/root /mnt/home
mount --mkdir -o noatime,compress=zstd,subvol=@cache /dev/mapper/root /mnt/var/cache
mount --mkdir -o noatime,compress=zstd,subvol=@log /dev/mapper/root /mnt/var/log
mount --mkdir -o noatime,compress=zstd,subvol=@tmp /dev/mapper/root /mnt/var/tmp
mount --mkdir -o noatime,compress=zstd,subvol=@snapshots /dev/mapper/root /mnt/.snapshots
mount --mkdir -o noatime,compress=zstd,subvol=@swap /dev/mapper/root /mnt/swap

Note

  • Most Btrfs mount options apply to the whole file system, not to individual subvolumes. That's why all subvolumes are mounted with the same options.
  • Other options that used to be set explicitly are default nowadays: space_cache=v2 (since btrfs-progs 5.15), ssd (detected automatically) and discard=async (since Linux 6.2, for devices that support it).

Mount the EFI partition:

mount --mkdir /dev/nvme0n1p1 /mnt/boot

Create a swap file (see Btrfs - Swap file). btrfs filesystem mkswapfile takes care of the Btrfs specifics, such as disabling copy-on-write and compression for the file:

btrfs filesystem mkswapfile --size <FILE-SIZE-IN-GiB>g --uuid clear /mnt/swap/swapfile
swapon /mnt/swap/swapfile

Base system and /etc/fstab

Install Arch Linux (adjust this list to your needs):

pacstrap -K /mnt linux linux-firmware base intel-ucode btrfs-progs efibootmgr gptfdisk dosfstools nano

Note

  • On a system with an AMD CPU, install amd-ucode instead of intel-ucode.
  • Don't forget to install network management software (e.g., networkmanager) and to enable its systemd unit. Otherwise, the new system has no network connection after the reboot.

Generate /etc/fstab:

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

Enable periodic trim

To enable periodic trim, execute

systemctl --root=/mnt enable fstrim.timer

Note

If your disk is not an SSD, you do not need this.

System configuration

Since I want a German system, the following steps are set up accordingly. Adjust them to your needs.

chroot into the new system:

arch-chroot /mnt/

Set host name:

echo <YOUR-HOSTNAME> > /etc/hostname

Set locale:

echo LANG=de_DE.UTF-8 > /etc/locale.conf

Uncomment the following lines of /etc/locale.gen:

#de_DE.UTF-8 UTF-8
#de_DE ISO-8859-1
#de_DE@euro ISO-8859-15

Generate locale:

locale-gen

Set keyboard layout and font:

echo KEYMAP=de-latin1 > /etc/vconsole.conf
echo FONT=lat9w-16 >> /etc/vconsole.conf

Set time zone:

ln -sf /usr/share/zoneinfo/Europe/Berlin /etc/localtime

Set the hardware clock and generate /etc/adjtime:

hwclock --systohc

Define hosts in /etc/hosts:

127.0.0.1   localhost
::1         localhost
127.0.1.1   <YOUR-HOSTNAME>.localdomain   <YOUR-HOSTNAME>

Set root password:

passwd

Initramfs

Configure the creation of initramfs by editing /etc/mkinitcpio.conf. Change the line HOOKS=... to:

HOOKS=(base systemd autodetect microcode modconf kms keyboard sd-vconsole block sd-encrypt filesystems fsck)

Note

  • Here, we are using a systemd-based RAM disk. It already contains everything required to resume from hibernation, so no resume hook is needed.
  • The btrfs hook is only required for Btrfs file systems that span multiple devices.

Recreate initramfs:

mkinitcpio -P

Boot manager

Install systemd-boot:

bootctl install

Since the ESP is mounted at /boot, bootctl finds it automatically. systemd-boot is updated automatically whenever the systemd package is upgraded.

Create the file /boot/loader/entries/archlinux.conf and fill it with:

title Arch Linux
linux /vmlinuz-linux
initrd /initramfs-linux.img
options rd.luks.name=<UUID-OF-SYSTEM-PARTITION>=root root=/dev/mapper/root rootflags=subvol=@ rd.luks.options=discard rw resume=/dev/mapper/root resume_offset=<SWAPFILE-OFFSET>

The offset of the swap file can be determined with this command:

btrfs inspect-internal map-swapfile -r /swap/swapfile

Note

  • Do not use filefrag to determine the offset (as recommended for other file systems). On Btrfs, it does not return the real physical offset on the disk.
  • If you don't use a swap file, leave out the options resume and resume_offset.
  • On UEFI systems, systemd stores the location of the hibernation image in an EFI variable when hibernating. Thus, resume and resume_offset are not strictly necessary. Specifying them explicitly is a fallback in case that mechanism does not work.

The UUID of the system partition (i.e., the LUKS container) can be determined via:

blkid -s UUID -o value /dev/nvme0n1p2

Edit the file /boot/loader/loader.conf and fill it with:

default  archlinux.conf
timeout  4
console-mode max
editor   no

Final steps

Exit chroot, unmount partitions and reboot:

exit
umount -R /mnt
reboot

Have fun with your system!

References

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