systemd-cryptsetup

systemd

systemd-cryptsetup

systemd-cryptsetup@.service

Full disk decryption logic

systemd-cryptsetup

OPTIONS

attach

VOLUME

SOURCE-DEVICE

KEY-FILE

CRYPTTAB-OPTIONS

systemd-cryptsetup

OPTIONS

detach

VOLUME

systemd-cryptsetup@.service

system-systemd\x2dcryptsetup.slice

Description

systemd-cryptsetup is used to set up (with attach) and tear down (with detach) access to an encrypted block device. It is primarily used via systemd-cryptsetup@.service during early boot, but may also be called manually. The positional arguments VOLUME, SOURCE-DEVICE, KEY-FILE, and CRYPTTAB-OPTIONS have the same meaning as the fields in crypttab(5).

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

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, 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:

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.
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.
If the try-empty-password option is specified then unlocking the volume with an empty password is attempted.
If the password-cache= option is set to yes or read-only, the kernel keyring is then checked for a suitable cached password from previous attempts.
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.

Credentials

systemd-cryptsetup supports the service credentials logic as implemented by ImportCredential=/LoadCredential=/SetCredential= (see systemd.exec(5) for details). The following credentials are used by systemd-crypsetup@root.service (generated by systemd-gpt-auto-generator) when passed in:

cryptsetup.passphrase
This credential specifies the passphrase of the LUKS volume.

cryptsetup.tpm2-pin
This credential specifies the TPM pin.

cryptsetup.fido2-pin
This credential specifies the FIDO2 token pin.

cryptsetup.pkcs11-pin
This credential specifies the PKCS11 token pin.

cryptsetup.luks2-pin
This credential specifies the pin requested by generic LUKS2 token modules.