29.4.6. Add the mapping information to /etc/crypttab

In order for the system to set up a mapping for the device, an entry must be present in the /etc/crypttab file. If the file doesn't exist, create it and change the owner and group to root (root:root) and change the mode to 0744. Add a line to the file with the following format:
<name>  <device>  none
The <device> field should be given in the form "UUID=<luks_uuid>", where <luks_uuid> is the LUKS uuid as given by the command cryptsetup luksUUID <device>. This ensures the correct device will be identified and used even if the device node (eg: /dev/sda5) changes.

Tip

For details on the format of the /etc/crypttab file, read the crypttab(5) man page.