17.4. Encrypting existing data on a block device using LUKS2

Procedure

1. Unmount all file systems on the device that you plan to encrypt, for example:

   # umount /dev/mapper/vg00-lv00

2. Make free space for storing a LUKS header. Use one of the following options that suits your scenario:

   • In the case of encrypting a logical volume, you can extend the logical volume without resizing the file system. For example:

     # lvextend -L+32M /dev/mapper/vg00-lv00

   • Extend the partition by using partition management tools, such as parted.
   • Shrink the file system on the device. You can use the resize2fs utility for the ext2, ext3, or ext4 file systems. Note that you cannot shrink the XFS file system.

3. Initialize the encryption:

   # cryptsetup reencrypt --encrypt --init-only --reduce-device-size 32M /dev/mapper/vg00-lv00 lv00_encrypted
   
   /dev/mapper/lv00_encrypted is now active and ready for online encryption.

4. Mount the device:

   # mount /dev/mapper/lv00_encrypted /mnt/lv00_encrypted

5. Add an entry for a persistent mapping to the /etc/crypttab file:

   1. Find the luksUUID:

      # cryptsetup luksUUID /dev/mapper/vg00-lv00
      
      a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325

   2. Open /etc/crypttab in a text editor of your choice and add a device in this file:

      $ vi /etc/crypttab
      
      lv00_encrypted UUID=a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325 none

      Replace a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325 with your device’s luksUUID.

   3. Refresh initramfs with dracut:

      $ dracut -f --regenerate-all

6. Ensure that if an entry for this device exists in the /etc/fstab file, it is using the filesystem UUID and not the device name.

7. Resume the online encryption:

   # cryptsetup reencrypt --resume-only /dev/mapper/vg00-lv00
   
   Enter passphrase for /dev/mapper/vg00-lv00:
   Auto-detected active dm device 'lv00_encrypted' for data device /dev/mapper/vg00-lv00.
   Finished, time 00:31.130, 10272 MiB written, speed 330.0 MiB/s

Verification

1. Verify if the existing data was encrypted:

   # cryptsetup luksDump /dev/mapper/vg00-lv00
   
   LUKS header information
   Version: 2
   Epoch: 4
   Metadata area: 16384 [bytes]
   Keyslots area: 16744448 [bytes]
   UUID: a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325
   Label: (no label)
   Subsystem: (no subsystem)
   Flags: (no flags)
   
   Data segments:
     0: crypt
   	offset: 33554432 [bytes]
   	length: (whole device)
   	cipher: aes-xts-plain64
   [...]

2. View the status of the encrypted blank block device:

   # cryptsetup status lv00_encrypted
   
   /dev/mapper/lv00_encrypted is active and is in use.
     type:    LUKS2
     cipher:  aes-xts-plain64
     keysize: 512 bits
     key location: keyring
     device:  /dev/mapper/vg00-lv00