systemd-cryptsetup - Man Page

Full disk decryption logic

Examples (TL;DR)

Open a LUKS volume and create a decrypted mapping at /dev/mapper/mapping_name: systemd-cryptsetup attach mapping_name /dev/sdXY
Open a LUKS volume with additional options and create a decrypted mapping at /dev/mapper/mapping_name: systemd-cryptsetup attach mapping_name /dev/sdXY none crypttab_options
Open a LUKS volume with a keyfile and create a decrypted mapping at /dev/mapper/mapping_name: systemd-cryptsetup attach mapping_name /dev/sdXY path/to/keyfile crypttab_options
Remove an existing mapping: systemd-cryptsetup detach mapping_name

tldr.sh

Synopsis

systemd-cryptsetup [OPTIONS...] attach VOLUME SOURCE-DEVICE [KEY-FILE] [CRYPTTAB-OPTIONS]

systemd-cryptsetup [OPTIONS...] detach VOLUME

systemd-cryptsetup@.service

system-systemd\x2dcryptsetup.slice

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^[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:

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.

Added in version 256.

cryptsetup.tpm2-pin

This credential specifies the TPM pin.

Added in version 256.

cryptsetup.fido2-pin

This credential specifies the FIDO2 token pin.

Added in version 256.

cryptsetup.pkcs11-pin

This credential specifies the PKCS11 token pin.

Added in version 256.