This guide was written specifically on Ubuntu, but it should work similarly on most modern Linux distributions.

Let's assume we have an existing device, formatted using LUKS and containing an ext4 filesystem. We want to automount it at boot, at a specific mount point location.

Find the name and uuid of the LUKS device

List all the LUKS devices in the system:

% lsblk --fs --json | jq '.blockdevices | .. | select(type == "object" and .fstype == "crypto_LUKS") | [.name,.fstype,.uuid] | @tsv' -r
sdx crypto_LUKS da2b593e-8c74-445e-aef6-f0b7f656d8c3

You can also use the "Disks" application, if you prefer using a GUI.

Enable key-based encryption

We need a way to unlock the device without typing in a passphrase. The solution is to use an encryption key stored in a file:

sudo mkdir /etc/luks-keys/
sudo chmod 700 /etc/luks-keys
sudo openssl genrsa -out /etc/luks-keys/default 2048

Add the key to the LUKS device:

sudo cryptsetup luksAddKey /dev/disk/by-uuid/da2b593e-8c74-445e-aef6-f0b7f656d8c3 /etc/luks-keys/default

Add an entry to /etc/crypttab

This allows the device to be unlocked automatically

echo "mydata UUID=da2b593e-8c74-445e-aef6-f0b7f656d8c3 /etc/luks-keys/default luks" | sudo tee -a /etc/crypttab

Open the newly added device

sudo cryptdisks_start mydata

Create a mount point

sudo mkdir /mnt/mydata

Add an entry to /etc/fstab

echo /dev/mapper/mydata /mnt/mydata auto defaults 0 0 | sudo tee -a /etc/fstab

Reload systemd

This will update systemd's internal fstab definition:

systemctl daemon-reload

Mount the filesystem

mount /mnt/mydata