dm-crypt/System configuration

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Notes: This article is currently under heavy restructuring: for its latest stable revision see Dm-crypt with LUKS (Discuss in Talk:Dm-crypt/System configuration#)

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Reason: Aggregate here all the generic information on system configuration from the other sub-articles of Dm-crypt. (Discuss in Talk:Dm-crypt/System configuration#)

Back to Dm-crypt.


When encrypting a system it is necessary to regenerate the initial ramdisk after properly configuring mkinitcpio. Depending on the particular scenarios, a subset of the following hooks will have to be enabled:

  • encrypt: always needed when encrypting the root partition, or a partition that needs to be mounted before root; it must come before the filesystems hook; it is not needed in all the other cases, as system initialization scripts like /etc/crypttab take care of unencrypting any other partitions.
  • shutdown: highly recommended, ensures controlled unmounting during system shutdown.
  • keymap: provides support for foreign keymaps for typing encryption passwords; it must come before the encrypt hook.
  • keyboard: needed to make USB keyboards work in early userspace.
    • usbinput: deprecated, but can be given a try in case keyboard does not work.

Other hooks needed should be clear from other manual steps followed during the installation of the system.

Boot loader

In order to enable booting an encrypted root partition, the following kernel paramaters need to be set. See kernel parameters for instructions specific to your boot loader.

The main parameter is cryptdevice, with the following syntax:

  • device is the path to the raw encrypted device. Usage of Persistent block device naming is advisable.
  • dmname is the device-mapper name given to the device after decryption, which will be available as /dev/mapper/dmname.

So if the encrypted root device in the example is /dev/sda2 and the decrypted one should be mapped to /dev/mapper/cryptroot, the kernel parameter would be:


This will make the system prompt for the passphrase to unlock the root device on a cold boot.

Depending on the setup other parameters are required as well:

cryptdevice=device:dmname root=device resume=device cryptkey=device:fstype:path
  • root=device is the device file of the actual (decrypted) root file system. If the file system is formatted directly on the decrypted device file this will be /dev/mapper/dmname.
  • resume=device is the device file of the decrypted (swap) filesystem used for suspend2disk. See also Dm-crypt/Swap Encryption.
  • cryptkey=device:fstype:path is required for reading a keyfile from a file system. See also Dm-crypt/Device Encryption#Using Cryptsetup with a Keyfile.
    • device is the raw block device where the key exists.
    • fstype is the filesystem type of device (or auto).
    • path is the absolute path of the keyfile within the device.