NAME

       systemd-cryptsetup@.service, systemd-cryptsetup - Full disk decryption logic

SYNOPSIS

       systemd-cryptsetup@.service

       system-systemd\x2dcryptsetup.slice

       /lib/systemd/systemd-cryptsetup

DESCRIPTION

       systemd-cryptsetup@.service is a service responsible for setting up encrypted block
       devices. It is instantiated for each device that requires decryption for access.

       systemd-cryptsetup@.service instances are part of the system-systemd\x2dcryptsetup.slice
       slice, which is destroyed only very late in the shutdown procedure. This allows the
       encrypted devices to remain up until filesystems have been unmounted.

       systemd-cryptsetup@.service will ask for hard disk passwords via the password agent
       logic[1], in order to query the user for the password using the right mechanism at boot
       and during runtime.

       At early boot and when the system manager configuration is reloaded, /etc/crypttab is
       translated into systemd-cryptsetup@.service units by systemd-cryptsetup-generator(8).

       In order to unlock a volume a password or binary key is required.
       systemd-cryptsetup@.service tries to acquire a suitable password or binary key via the
       following mechanisms, tried in order:

        1. If a key file is explicitly configured (via the third column in /etc/crypttab), a key
           read from it is used. If a PKCS#11 token, FIDO2 token or TPM2 device is configured
           (using the pkcs11-uri=, fido2-device=, tpm2-device= options) the key is decrypted
           before use.

        2. If no key file is configured explicitly this way, a key file is automatically loaded
           from /etc/cryptsetup-keys.d/volume.key and /run/cryptsetup-keys.d/volume.key, if
           present. Here too, if a PKCS#11/FIDO2/TPM2 token/device is configured, any key found
           this way is decrypted before use.

        3. If the try-empty-password option is specified it is then attempted to unlock the
           volume with an empty password.

        4. The kernel keyring is then checked for a suitable cached password from previous
           attempts.

        5. Finally, the user is queried for a password, possibly multiple times, unless the
           headless option is set.

       If no suitable key may be acquired via any of the mechanisms describes above, volume
       activation fails.

SEE ALSO

       systemd(1), systemd-cryptsetup-generator(8), crypttab(5), systemd-cryptenroll(1),
       cryptsetup(8)

NOTES

        1. password agent logic
           https://systemd.io/PASSWORD_AGENTS/