LUKS related directories in root of a Debian 11

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i am wondering what creates and touches on a Debian 11 system a lot of
empty directories in the /-Directory. The names indicate that they have
something to do with LUKS:

  /1678114330.LUKS1_test_cryptsetup_defaults
  /1678114331.LUKS1_test_with_twofish_cipher
  ...
  /1678114341.LUKS2_test_cryptsetup_defaults
  /1678114342.LUKS2_test_with_twofish_cipher
  ...
  /1680340570.LUKS2_test_with_argon2_pbkdf
  /1680340571.LUKS2_test_with_second_key_slot_and_first_slot_using_different_password

In total there are 115 of these directories. Currently all are empty.
One of them bears the timestamp of today's boot:
   /1678114330.LUKS1_test_cryptsetup_defaults
(Its prefix number as timestamp says "Mon Mar  6 15:52:10 CET 2023")
A few bear the timestamp "Apr  1  2023" and most bear "Mar  6  2023".

One of the partitions on the system is indeed encrypted. But the
root filesystem is not. df says about both:

  /dev/nvme0n1p2     479152840   92955444  361788004  21% /
  ...
  /dev/mapper/daten 3778568692 1538634024 2047923672  43% /daten

So my questions are:
- Where can i learn about those directories ?
- Why are they located in / and not in some sub-directory ?


Have a nice day :)

Thomas