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systemd-cryptsetup@.service, systemd-cryptsetup − Full disk decryption logic
systemd−cryptsetup@.service
system−systemd\x2dcryptsetup.slice
/usr/lib/systemd/systemd−cryptsetup
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.
systemd(1), systemd-cryptsetup-generator(8), crypttab(5), systemd-cryptenroll(1), cryptsetup(8)
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1. |
password agent logic |
https://systemd.io/PASSWORD_AGENTS/