Removing system encryption with dm-crypt and LUKS.
Removing LUKS Encryption in-place
Although not as safe as backing up your data and restoring it on to a reformatted device, cryptsetup does allow the user to permanently remove the LUKS encryption from a device in-place. For example, if you have an ext4 filesystem living inside a LUKS-encrypted partition, performing in-place decryption will remove the LUKS signature, and place the ext4 filesystem directly on the partition, so that you can mount it directly. Unless something goes wrong, the files in the filesystem will remain intact. The terms used by cryptsetup's documentation for this is "decryption."
Support for non-destructive offline decryption of LUKS1 devices has been available starting with
cryptsetup version 1.5.0, which was released in 2012. LUKS1 decryption is only supported for offline mode decryption.
For LUKS2 devices, both offline and online (i.e. unmount not required) decryption are supported.
Decrypting LUKS1 devices in-place
The decryption of a LUKS1 device is done in offline mode, i.e. it must not opened and mounted. If you want to decrypt the system drive, reboot into a USB live environment. Otherwise, use
unmount followed by
cryptsetup close dm-name.
To start, identify the device_path using
Next, the following command performs the decryption:
# cryptsetup reencrypt --decrypt device_path Enter any existing passphrase: Finished, time 02m05s, 19 GiB written, speed 162,6 MiB/s
It will automatically identify the LUKS1 header version and not proceed for an opened device. The process might take a while, but give a progress meter. If no problems occur, the filesystem on the device can immediately be mounted directly.
Decrypting LUKS2 devices in-place
Decryption can be done in either offline or online mode, using the
cryptsetup command. Since
cryptsetup version 2.5.0 (2022) LUKS2 supports decryption by migrating LUKS2 header in a separate file.
new_file to which the LUKS2 header will be be migrated must not exist in the initialization phase of the decryption.
# cryptsetup reencrypt --decrypt --header new_file device_path
To resume interrupted LUKS2 in-place decryption just issue following command:
# cryptsetup reencrypt --decrypt --resume-only --header migrated_header_file device_path
If the decryption was successfully finished on active device (online decryption), the mapped device will be lazy deactivated so that linear mapping is automatically removed when no longer used. Later the original
device_path can be used without device mapper mapping.
Cleaning up system files
Device names and UUIDs may change due to decryption, and you will likely need to update relevant configuration files. The files most likely to need updating are
/etc/fstab and, if your recently decrypted device appeared on the kernel command line, your bootloader's configuration (e.g,
/etc/default/grub). If you edit the latter, remember to regenerate the grub configuration as described in GRUB.
Removing LUKS via Backup-Format-Restore
- An encrypted root filesystem you wish to decrypt.
- Enough drive space to store a backup.
- An Arch Linux (or other) live CD/USB.
- A few hours.
Boot into a live environment
Download and burn the latest Arch ISO to a CD or USB, reboot the system, and boot to cd.
Note about different setups
An example setup is shown here:
The grey partition is a frame of reference and can be ignored. The yellow partition will be used as storage space and may be changed at will. The green partitions will be modified. Bold text must match your system's setup.
In the example system:
myvg contains lvs called cryptroot and cryptswap. They are located at
/dev/myvg/cryptswap. Upon boot, LUKS is used along with a few crypttab entries to create
Swap will not be unencrypted as part of this guide, as undoing the swap encryption does not require any complex backup or restoration.
The example system is not indicative of all systems. Different filesystems require different tools to effectively backup and restore their data. LVM can be ignored if not used.
Once partitions are located
Load necessary modules. For device mapper/LVM:
# modprobe dm-mod
# modprobe dm-crypt
Scan for physical, volume and logical volumes:
# pvscan; vgscan; lvscan
Activate the LVM volume group:
# lvchange -ay myvg/cryptroot
Open the encrypted filesystem with LUKS so that it can be read:
# cryptsetup luksOpen /dev/myvg/cryptroot root
Mounting backup space
Only if using NTFS to store the backup, install.
The next step is important for backup storage.
# mount -t ntfs-3g -o rw /dev/sdXY /mount/point/
or use netcat to store the backup on a remote system.
# xfs_copy -db /dev/mapper/root /mount/point/backup_root.img
-d flag preserves UUIDs and
-b ensures direct IO is not attempted to any of the target files.
# dd if=/dev/mapper/root of=/mount/point/backup_root.img
This is the point of no return. Make sure that you are ready for this step. If you plan to undo this later, you will have to start almost from scratch.
# cryptsetup luksClose root # lvm lvremove myvg/cryptroot
We have to create a new logical volume to house our root filesystem, then we restore our filesystem.
# lvm lvcreate -l 100%FREE -n root myvg # xfs_copy -db /mount/point/backup_root.img /dev/myvg/root
The second drive name is changed now.
You need to boot into your system and edit
/etc/fstab, and possibly