# crypttab

## NAME



           crypttab - Configuration for encrypted block devices
    


## SYNOPSIS



           /etc/crypttab
    


## DESCRIPTION



           The /etc/crypttab file describes encrypted block devices that are
           set up during system boot.
    
           Empty lines and lines starting with the "#" character are ignored.
           Each of the remaining lines describes one encrypted block device.
           Fields are delimited by white space.
    
           Each line is in the form
    
               _volume-name encrypted-device key-file options_
    
           The first two fields are mandatory, the remaining two are
           optional.
    
           Setting up encrypted block devices using this file supports four
           encryption modes: LUKS, TrueCrypt, BitLocker and plain. See
           cryptsetup(8) for more information about each mode. When no mode
           is specified in the options field and the block device contains a
           LUKS signature, it is opened as a LUKS device; otherwise, it is
           assumed to be in raw dm-crypt (plain mode) format.
    
           The four fields of /etc/crypttab are defined as follows:
    
            1. The first field contains the name of the resulting volume with
               decrypted data; its block device is set up below /dev/mapper/.
    
            2. The second field contains a path to the underlying block
               device or file, or a specification of a block device via
               "UUID=" followed by the UUID.
    
            3. The third field specifies an absolute path to a file with the
               encryption key. Optionally, the path may be followed by ":"
               and an /etc/fstab style device specification (e.g. starting
               with "LABEL=" or similar); in which case the path is taken
               relative to the specified device's file system root. If the
               field is not present or is "none" or "-", a key file named
               after the volume to unlock (i.e. the first column of the
               line), suffixed with .key is automatically loaded from the
               /etc/cryptsetup-keys.d/ and /run/cryptsetup-keys.d/
               directories, if present. Otherwise, the password has to be
               manually entered during system boot. For swap encryption,
               /dev/urandom may be used as key file, resulting in a
               randomized key.
    
               If the specified key file path refers to an **AF_UNIX** stream
               socket in the file system, the key is acquired by connecting
               to the socket and reading it from the connection. This allows
               the implementation of a service to provide key information
               dynamically, at the moment when it is needed. For details see
               below.
    
            4. The fourth field, if present, is a comma-delimited list of
               options. The supported options are listed below.
    


## KEY ACQUISITION



           Six different mechanisms for acquiring the decryption key or
           passphrase unlocking the encrypted volume are supported.
           Specifically:
    
            1. Most prominently, the user may be queried interactively during
               volume activation (i.e. typically at boot), asking them to
               type in the necessary passphrases.
    
            2. The (unencrypted) key may be read from a file on disk,
               possibly on removable media. The third field of each line
               encodes the location, for details see above.
    
            3. The (unencrypted) key may be requested from another service,
               by specifying an **AF_UNIX** file system socket in place of a key
               file in the third field. For details see above and below.
    
            4. The key may be acquired via a PKCS#11 compatible hardware
               security token or smartcard. In this case, a saved key used in
               unlock process is stored on disk/removable media, acquired via
               **AF_UNIX** , or stored in the LUKS2 JSON token metadata header.
               For RSA, the saved key is an encrypted volume key. The
               encrypted volume key is then decrypted by the PKCS#11 token
               with an RSA private key stored on it, and used to unlock the
               encrypted volume. For elliptic-curve (EC) cryptography, the
               saved key is the public key generated in enrollment process.
               The public key is then used to derive a shared secret with a
               private key stored in the PKCS#11 token. The derived shared
               secret is then used to unlock the volume. Use the **pkcs11-uri=**
               option described below to use this mechanism.
    
            5. Similarly, the key may be acquired via a FIDO2 compatible
               hardware security token (which must implement the
               "hmac-secret" extension). In this case, a key generated
               randomly during enrollment is stored on disk/removable media,
               acquired via **AF_UNIX** , or stored in the LUKS2 JSON token
               metadata header. The random key is hashed via a keyed hash
               function (HMAC) on the FIDO2 token, using a secret key stored
               on the token that never leaves it. The resulting hash value is
               then used as key to unlock the encrypted volume. Use the
               **fido2-device=** option described below to use this mechanism.
    
            6. Similarly, the key may be acquired via a TPM2 security chip.
               In this case, a (during enrollment) randomly generated key —
               encrypted by an asymmetric key derived from the TPM2 chip's
               seed key — is stored on disk/removable media, acquired via
               **AF_UNIX** , or stored in the LUKS2 JSON token metadata header.
               Use the **tpm2-device=** option described below to use this
               mechanism.
    
           For the latter five mechanisms the source for the key material
           used for unlocking the volume is primarily configured in the third
           field of each /etc/crypttab line, but may also be configured in
           /etc/cryptsetup-keys.d/ and /run/cryptsetup-keys.d/ (see above) or
           in the LUKS2 JSON token header (in case of the latter three). Use
           the systemd-cryptenroll(1) tool to enroll PKCS#11, FIDO2 and TPM2
           devices in LUKS2 volumes.
    


## SUPPORTED OPTIONS



           The following options may be used in the fourth field of each
           line:
    
           **cipher=**
               Specifies the cipher to use. See cryptsetup(8) for possible
               values and the default value of this option. A cipher with
               unpredictable IV values, such as "aes-cbc-essiv:sha256", is
               recommended. Embedded commas in the cipher specification need
               to be escaped by preceding them with a backslash, see example
               below.
    
               Added in version 186.
    
           **discard**
               Allow discard requests to be passed through the encrypted
               block device. This improves performance on SSD storage but has
               security implications.
    
               Added in version 207.
    
           **hash=**
               Specifies the hash to use for password hashing. See
               cryptsetup(8) for possible values and the default value of
               this option.
    
               Added in version 186.
    
           **header=**
               Use a detached (separated) metadata device or file where the
               header containing the master key(s) is stored. This option is
               only relevant for LUKS and TrueCrypt/VeraCrypt devices. See
               cryptsetup(8) for possible values and the default value of
               this option.
    
               Optionally, the path may be followed by ":" and an /etc/fstab
               device specification (e.g. starting with "UUID=" or similar);
               in which case, the path is relative to the device file system
               root. The device gets mounted automatically for LUKS device
               activation duration only.
    
               Added in version 219.
    
           **keyfile-offset=**
               Specifies the number of bytes to skip at the start of the key
               file. See cryptsetup(8) for possible values and the default
               value of this option.
    
               Added in version 187.
    
           **keyfile-size=**
               Specifies the maximum number of bytes to read from the key
               file. See cryptsetup(8) for possible values and the default
               value of this option. This option is ignored in plain
               encryption mode, where the key file size is determined by the
               key size. It is also ignored when the key file is used as a
               salt file for a FIDO2 token, as the salt size in that case is
               defined by the FIDO2 specification to be exactly 32 bytes.
    
               Added in version 188.
    
           **keyfile-erase**
               If enabled, the specified key file is erased after the volume
               is activated or when activation fails. This is in particular
               useful when the key file is only acquired transiently before
               activation (e.g. via a file in /run/, generated by a service
               running before activation), and shall be removed after use.
               Defaults to off.
    
               Added in version 246.
    
           **key-slot=**
               Specifies the key slot to compare the passphrase or key
               against. If the key slot does not match the given passphrase
               or key, but another would, the setup of the device will fail
               regardless. This option implies **luks**. See cryptsetup(8) for
               possible values. The default is to try all key slots in
               sequential order.
    
               Added in version 209.
    
           **keyfile-timeout=**
               Specifies the timeout for the device on which the key file
               resides or the device used as the key file, and falls back to
               a password if it could not be accessed. See
               systemd-cryptsetup-generator(8) for key files on external
               devices.
    
               Added in version 243.
    
           **link-volume-key=**
               Specifies the kernel keyring and key description (see
               keyrings(7)) where LUKS2 volume key gets linked during device
               activation. The kernel keyring description and key description
               must be separated by "::".
    
               The kernel keyring part can be a string description or a
               predefined kernel keyring prefixed with "@" (e.g.: to use "@s"
               session or "@u" user keyring directly). The type prefix text
               in the kernel keyring description is not required. The
               specified kernel keyring must already exist at the time of
               device activation.
    
               The key part is a string description optionally prefixed by a
               "%key_type:". If no type is specified, the "user" type key is
               linked by default. See keyctl(1) for more information on key
               descriptions (KEY IDENTIFIERS section).
    
               Note that the linked volume key is not cleaned up
               automatically when the device is detached.
    
               Added in version 256.
    
           **luks**
               Force LUKS mode. When this mode is used, the following options
               are ignored since they are provided by the LUKS header on the
               device: **cipher=** , **hash=** , **size=**.
    
               Added in version 186.
    
           **bitlk**
               Decrypt BitLocker drive. Encryption parameters are deduced by
               cryptsetup from BitLocker header.
    
               Added in version 246.
    
           **_netdev**
               Marks this cryptsetup device as requiring network. It will be
               started after the network is available, similarly to
               systemd.mount(5) units marked with **_netdev**. The service unit
               to set up this device will be ordered between
               remote-fs-pre.target and remote-cryptsetup.target, instead of
               cryptsetup-pre.target and cryptsetup.target.
    
               Hint: if this device is used for a mount point that is
               specified in fstab(5), the **_netdev** option should also be used
               for the mount point. Otherwise, a dependency loop might be
               created where the mount point will be pulled in by
               local-fs.target, while the service to configure the network is
               usually only started _after_ the local file system has been
               mounted.
    
               Added in version 235.
    
           **noauto**
               This device will not be added to cryptsetup.target. This means
               that it will not be automatically unlocked on boot, unless
               something else pulls it in. In particular, if the device is
               used for a mount point, it'll be unlocked automatically during
               boot, unless the mount point itself is also disabled with
               **noauto**.
    
               Added in version 186.
    
           **nofail**
               This device will not be a hard dependency of
               cryptsetup.target. It'll still be pulled in and started, but
               the system will not wait for the device to show up and be
               unlocked, and boot will not fail if this is unsuccessful. Note
               that other units that depend on the unlocked device may still
               fail. In particular, if the device is used for a mount point,
               the mount point itself also needs to have the **nofail** option,
               or the boot will fail if the device is not unlocked
               successfully. If a keyfile and/or a **header** are specified, the
               dependencies on their respective directories will also not be
               fatal, so that umounting said directories will not cause the
               generated cryptset unit to be deactivated.
    
               Added in version 186.
    
           **offset=**
               Start offset in the backend device, in 512-byte sectors. This
               option is only relevant for plain devices.
    
               Added in version 220.
    
           **plain**
               Force plain encryption mode.
    
               Added in version 186.
    
           **read-only** , **readonly**
               Set up the encrypted block device in read-only mode.
    
               Added in version 186.
    
           **same-cpu-crypt**
               Perform encryption using the same CPU that IO was submitted
               on. The default is to use an unbound workqueue so that
               encryption work is automatically balanced between available
               CPUs.
    
               This requires kernel 4.0 or newer.
    
               Added in version 242.
    
           **submit-from-crypt-cpus**
               Disable offloading writes to a separate thread after
               encryption. There are some situations where offloading write
               requests from the encryption threads to a dedicated thread
               degrades performance significantly. The default is to offload
               write requests to a dedicated thread because it benefits the
               CFQ scheduler to have writes submitted using the same context.
    
               This requires kernel 4.0 or newer.
    
               Added in version 242.
    
           **no-read-workqueue**
               Bypass dm-crypt internal workqueue and process read requests
               synchronously. The default is to queue these requests and
               process them asynchronously.
    
               This requires kernel 5.9 or newer.
    
               Added in version 248.
    
           **no-write-workqueue**
               Bypass dm-crypt internal workqueue and process write requests
               synchronously. The default is to queue these requests and
               process them asynchronously.
    
               This requires kernel 5.9 or newer.
    
               Added in version 248.
    
           **skip=**
               How many 512-byte sectors of the encrypted data to skip at the
               beginning. This is different from the **offset=** option with
               respect to the sector numbers used in initialization vector
               (IV) calculation. Using **offset=** will shift the IV calculation
               by the same negative amount. Hence, if **offset=**_n_ is given,
               sector _n_ will get a sector number of 0 for the IV calculation.
               Using **skip=** causes sector _n_ to also be the first sector of the
               mapped device, but with its number for IV generation being _n_.
    
               This option is only relevant for plain devices.
    
               Added in version 220.
    
           **size=**
               Specifies the key size in bits. See cryptsetup(8) for possible
               values and the default value of this option.
    
               Added in version 186.
    
           **sector-size=**
               Specifies the sector size in bytes. See cryptsetup(8) for
               possible values and the default value of this option.
    
               Added in version 240.
    
           **swap**
               The encrypted block device will be used as a swap device, and
               will be formatted accordingly after setting up the encrypted
               block device, with mkswap(8). This option implies **plain**.
    
                   **Warning**
                   Using the **swap** option will destroy the contents of the
                   named partition during every boot, so make sure the
                   underlying block device is specified correctly.
               Added in version 186.
    
           **tcrypt**
               Use TrueCrypt encryption mode. When this mode is used, the
               following options are ignored since they are provided by the
               TrueCrypt header on the device or do not apply: **cipher=** ,
               **hash=** , **keyfile-offset=** , **keyfile-size=** , **size=**.
    
               When this mode is used, the passphrase is read from the key
               file given in the third field. Only the first line of this
               file is read, excluding the new line character.
    
               Note that the TrueCrypt format uses both passphrase and key
               files to derive a password for the volume. Therefore, the
               passphrase and all key files need to be provided. Use
               **tcrypt-keyfile=** to provide the absolute path to all key files.
               When using an empty passphrase in combination with one or more
               key files, use "/dev/null" as the password file in the third
               field.
    
               Added in version 206.
    
           **tcrypt-hidden**
               Use the hidden TrueCrypt volume. This option implies **tcrypt**.
    
               This will map the hidden volume that is inside of the volume
               provided in the second field. Please note that there is no
               protection for the hidden volume if the outer volume is
               mounted instead. See cryptsetup(8) for more information on
               this limitation.
    
               Added in version 206.
    
           **tcrypt-keyfile=**
               Specifies the absolute path to a key file to use for a
               TrueCrypt volume. This implies **tcrypt** and can be used more
               than once to provide several key files.
    
               See the entry for **tcrypt** on the behavior of the passphrase and
               key files when using TrueCrypt encryption mode.
    
               Added in version 206.
    
           **tcrypt-system**
               Use TrueCrypt in system encryption mode. This option implies
               **tcrypt**.
    
               Added in version 206.
    
           **tcrypt-veracrypt**
               Check for a VeraCrypt volume. VeraCrypt is a fork of TrueCrypt
               that is mostly compatible, but uses different, stronger key
               derivation algorithms that cannot be detected without this
               flag. Enabling this option could substantially slow down
               unlocking, because VeraCrypt's key derivation takes much
               longer than TrueCrypt's. This option implies **tcrypt**.
    
               Added in version 232.
    
           **veracrypt-pim=**
               Specifies a custom Personal Iteration Multiplier (PIM) value,
               which can range from 0..2147468 for standard veracrypt volumes
               and 0..65535 for veracrypt system volumes. A value of 0 will
               imply the VeraCrypt default. This option is only effective
               when **tcrypt-veracrypt** is set.
    
               Note that VeraCrypt enforces a minimal allowed PIM value
               depending on the password strength and the hash algorithm used
               for key derivation, however **veracrypt-pim=** is not checked
               against these bounds. See **Veracrypt Personal Iterations**
               **Multiplier******[1] documentation for more information.
    
               Added in version 254.**timeout=**
               Specifies the timeout for querying for a password. If no unit
               is specified, seconds is used. Supported units are s, ms, us,
               min, h, d. A timeout of 0 waits indefinitely (which is the
               default).
    
               Added in version 186.
    
           **tmp=**
               The encrypted block device will be prepared for using it as
               /tmp/; it will be formatted using mkfs(8). Takes a file system
               type as argument, such as "ext4", "xfs" or "btrfs". If no
               argument is specified defaults to "ext4". This option implies
               **plain**.
    
                   **Warning**
                   Using the **tmp** option will destroy the contents of the
                   named partition during every boot, so make sure the
                   underlying block device is specified correctly.
               Added in version 186.
    
           **tries=**
               Specifies the maximum number of times the user is queried for
               a password. The default is 3. If set to 0, the user is queried
               for a password indefinitely.
    
               Added in version 186.
    
           **headless=**
               Takes a boolean argument, defaults to false. If true, never
               query interactively for the password/PIN. Useful for headless
               systems.
    
               Added in version 249.
    
           **verify**
               If the encryption password is read from console, it has to be
               entered twice to prevent typos.
    
               Added in version 186.
    
           **password-echo=yes|no|masked**
               Controls whether to echo passwords or security token PINs that
               are read from console. Takes a boolean or the special string
               "masked". The default is **password-echo=masked**.
    
               If enabled, the typed characters are echoed literally. If
               disabled, the typed characters are not echoed in any form, the
               user will not get feedback on their input. If set to "masked",
               an asterisk ("*") is echoed for each character typed.
               Regardless of which mode is chosen, if the user hits the
               tabulator key ("↹") at any time, or the backspace key ("⌫")
               before any other data has been entered, then echo is turned
               off.
    
               Added in version 249.
    
           **password-cache=yes|no|read-only**
               Controls whether to use cache for passwords or security token
               PINs. Takes a boolean or the special string "read-only".
               Defaults to "yes".
    
               If set to "read-only", the kernel keyring is checked for a
               password/PIN before requesting one interactively. If set to
               "yes", in addition to checking the keyring, any password/PIN
               entered interactively is cached in the keyring with a
               2.5-minute timeout before being purged.
    
               Note that this option is not permitted for PKCS#11 security
               tokens. The reasoning behind this is that PKCS#11 security
               tokens are usually configured to lock after being supplied an
               invalid PIN multiple times, so using the cache might
               inadvertently lock the token.
    
               Added in version 257.
    
           **pkcs11-uri=**
               Takes either the special value "auto" or an **RFC7512 PKCS#11**
               **URI******[2] pointing to a private key which is used to decrypt the
               encrypted key specified in the third column of the line. This
               is useful for unlocking encrypted volumes through PKCS#11
               compatible security tokens or smartcards. See below for an
               example how to set up this mechanism for unlocking a LUKS2
               volume with a YubiKey security token.
    
               If specified as "auto" the volume must be of type LUKS2 and
               must carry PKCS#11 security token metadata in its LUKS2 JSON
               token section. In this mode the URI and the encrypted key are
               automatically read from the LUKS2 JSON token header. Usesystemd-cryptenroll(1) as a simple tool for enrolling PKCS#11
               security tokens or smartcards in a way compatible with "auto".
               In this mode the third column of the line should remain empty
               (that is, specified as "-").
    
               The specified URI can refer directly to a private key stored
               on a token or alternatively just to a slot or token, in which
               case a search for a suitable private key will be performed. In
               this case, if multiple suitable objects are found, the token
               is refused. The keyfile configured in the third column of the
               line is used as is (i.e. in binary form, unprocessed). The
               resulting decrypted key (for RSA) or derived shared secret
               (for ECC) is then Base64 encoded before it is used to unlock
               the LUKS volume.
    
               Use **systemd-cryptenroll --pkcs11-token-uri=list** to list all
               suitable PKCS#11 security tokens currently plugged in, along
               with their URIs.
    
               Note that many newer security tokens that may be used as
               PKCS#11 security token typically also implement the newer and
               simpler FIDO2 standard. Consider using **fido2-device=**
               (described below) to enroll it via FIDO2 instead. Note that a
               security token enrolled via PKCS#11 cannot be used to unlock
               the volume via FIDO2, unless also enrolled via FIDO2, and vice
               versa.
    
               Added in version 245.
    
           **fido2-device=**
               Takes either the special value "auto" or the path to a
               "hidraw" device node (e.g.  /dev/hidraw1) referring to a FIDO2
               security token that implements the "hmac-secret" extension
               (most current hardware security tokens do). See below for an
               example how to set up this mechanism for unlocking an
               encrypted volume with a FIDO2 security token.
    
               If specified as "auto" the FIDO2 token device is automatically
               discovered, as it is plugged in.
    
               FIDO2 volume unlocking requires a client ID hash (CID) to be
               configured via **fido2-cid=**(see below) and a key to pass to the
               security token's HMAC functionality (configured in the line's
               third column) to operate. If not configured and the volume is
               of type LUKS2, the CID and the key are read from LUKS2 JSON
               token metadata instead. Use systemd-cryptenroll(1) as simple
               tool for enrolling FIDO2 security tokens for LUKS2 volumes.
    
               Use **systemd-cryptenroll --fido2-device=list** to list all
               suitable FIDO2 security tokens currently plugged in, along
               with their device nodes.
    
               This option implements the following mechanism: the configured
               key is hashed via they HMAC keyed hash function the FIDO2
               device implements, keyed by a secret key embedded on the
               device. The resulting hash value is Base64 encoded and used to
               unlock the LUKS2 volume. As it should not be possible to
               extract the secret from the hardware token, it should not be
               possible to retrieve the hashed key given the configured key —
               without possessing the hardware token.
    
               Note that many security tokens that implement FIDO2 also
               implement PKCS#11, suitable for unlocking volumes via the
               **pkcs11-uri=** option described above. Typically the newer,
               simpler FIDO2 standard is preferable.
    
               Added in version 248.
    
           **fido2-cid=**
               Takes a Base64 encoded FIDO2 client ID to use for the FIDO2
               unlock operation. If specified, but **fido2-device=** is not,
               **fido2-device=auto** is implied. If **fido2-device=** is used but
               **fido2-cid=** is not, the volume must be of LUKS2 type, and the
               CID is read from the LUKS2 JSON token header. Use
               systemd-cryptenroll(1) for enrolling a FIDO2 token in the
               LUKS2 header compatible with this automatic mode.
    
               Added in version 248.
    
           **fido2-rp=**
               Takes a string, configuring the FIDO2 Relying Party (rp) for
               the FIDO2 unlock operation. If not specified,
               "io.systemd.cryptsetup" is used, except if the LUKS2 JSON
               token header contains a different value. It should normally
               not be necessary to override this.
    
               Added in version 248.
    
           **fido2-pin=**
               Controls whether to require the user to enter a PIN when
               unlocking the volume (the FIDO2 "clientPin" feature). This
               option only applies when in manual mode, i.e. when **fido2-cid=**
               option is set. Defaults to neither true or false, but rather
               to **v248** behavior, that is: try with no PIN first, but if token
               reports that PIN is required, try again asking for PIN.
    
               Added in version 257.
    
           **fido2-up=**
               Controls whether to require the user to verify presence (tap
               the token, the FIDO2 "up" feature) when unlocking the volume.
               This option only applies when in manual mode, i.e. when
               **fido2-cid=** option is set. Defaults to neither true or false,
               but rather to **v248** behavior, that is: try with no UP first,
               but if token reports that UP is required, try again with UP
               enabled.
    
               Added in version 257.
    
           **fido2-uv=**
               Controls whether to require user verification (the FIDO2 "uv"
               feature) when unlocking the volume. This option only applies
               when in manual mode, i.e. when **fido2-cid=** option is set.
               Defaults to neither true or false, but rather to **v248**
               behavior, that is: omit configuring UV whatsoever.
    
               Added in version 257.
    
           **tpm2-device=**
               Takes either the special value "auto" or the path to a device
               node (e.g.  /dev/tpmrm0) referring to a TPM2 security chip.
               See below for an example how to set up this mechanism for
               unlocking an encrypted volume with a TPM2 chip.
    
               Use **tpm2-pcrs=**(see below) to configure the set of TPM2 PCRs
               to bind the volume unlocking to. Use systemd-cryptenroll(1) as
               simple tool for enrolling TPM2 security chips in LUKS2
               volumes.
    
               If specified as "auto" the TPM2 device is automatically
               discovered. Use **systemd-cryptenroll --tpm2-device=list** to list
               all suitable TPM2 devices currently available, along with
               their device nodes.
    
               This option implements the following mechanism: when enrolling
               a TPM2 device via **systemd-cryptenroll** on a LUKS2 volume, a
               randomized key unlocking the volume is generated on the host
               and loaded into the TPM2 chip where it is encrypted with an
               asymmetric "primary" key pair derived from the TPM2's internal
               "seed" key. Neither the seed key nor the primary key are
               permitted to ever leave the TPM2 chip — however, the now
               encrypted randomized key may. It is saved in the LUKS2 volume
               JSON token header. When unlocking the encrypted volume, the
               primary key pair is generated on the TPM2 chip again (which
               works as long as the chip's seed key is correctly maintained
               by the TPM2 chip), which is then used to decrypt (on the TPM2
               chip) the encrypted key from the LUKS2 volume JSON token
               header saved there during enrollment. The resulting decrypted
               key is then used to unlock the volume. When the randomized key
               is encrypted the current values of the selected PCRs (see
               below) are included in the operation, so that different PCR
               state results in different encrypted keys and the decrypted
               key can only be recovered if the same PCR state is reproduced.
    
               Added in version 248.
    
           **tpm2-pcrs=**
               Takes a "+" separated list of numeric TPM2 PCR (i.e. "Platform
               Configuration Register") indexes to bind the TPM2 volume
               unlocking to. This option is only useful when TPM2 enrollment
               metadata is not available in the LUKS2 JSON token header
               already, the way **systemd-cryptenroll** writes it there. If not
               used (and no metadata in the LUKS2 JSON token header defines
               it), defaults to a list of a single entry: PCR 7. Assign an
               empty string to encode a policy that binds the key to no PCRs,
               making the key accessible to local programs regardless of the
               current PCR state.
    
               Added in version 248.
    
           **tpm2-pin=**
               Takes a boolean argument, defaults to "false". Controls
               whether TPM2 volume unlocking is bound to a PIN in addition to
               PCRs. Similarly, this option is only useful when TPM2
               enrollment metadata is not available.
    
               Added in version 251.
    
           **tpm2-signature=**
               Takes an absolute path to a TPM2 PCR JSON signature file, as
               produced by the systemd-measure(1) tool. This permits locking
               LUKS2 volumes to any PCR values for which a valid signature
               matching a public key specified at key enrollment time can be
               provided. See systemd-cryptenroll(1) for details on enrolling
               TPM2 PCR public keys. If this option is not specified but it
               is attempted to unlock a LUKS2 volume with a signed TPM2 PCR
               enrollment, a suitable signature file tpm2-pcr-signature.json
               is searched for in /etc/systemd/, /run/systemd/,
               /usr/lib/systemd/ (in this order).
    
               Added in version 252.
    
           **tpm2-pcrlock=**
               Takes an absolute path to a TPM2 pcrlock policy file, as
               produced by the systemd-pcrlock(8) tool. This permits locking
               LUKS2 volumes to a local policy of allowed PCR values with
               variants. See systemd-cryptenroll(1) for details on enrolling
               TPM2 pcrlock policies. If this option is not specified but it
               is attempted to unlock a LUKS2 volume with a TPM2 pcrlock
               enrollment, a suitable signature file pcrlock.json is searched
               for in /run/systemd/ and /var/lib/systemd/ (in this order).
    
               Added in version 255.
    
           **tpm2-measure-pcr=**
               Controls whether to measure the volume key of the encrypted
               volume to a TPM2 PCR. If set to "no" (which is the default) no
               PCR extension is done. If set to "yes" the volume key is
               measured into PCR 15. If set to a decimal integer in the range
               0...23 the volume key is measured into the specified PCR. The
               volume key is measured along with the activated volume name
               and its UUID. This functionality is particularly useful for
               the encrypted volume backing the root file system, as it then
               allows later TPM objects to be securely bound to the root file
               system and hence the specific installation.
    
               Added in version 253.
    
           **tpm2-measure-bank=**
               Selects one or more TPM2 PCR banks to measure the volume key
               into, as configured with **tpm2-measure-pcr=** above. Multiple
               banks may be specified, separated by a colon character. If not
               specified, automatically determines available and used banks.
               Expects a message digest name (e.g.  "sha1", "sha256", ...) as
               argument, to identify the bank.
    
               Added in version 253.
    
           **token-timeout=**
               Specifies how long to wait at most for configured security
               devices (i.e. FIDO2, PKCS#11, TPM2) to show up. Takes a time
               value in seconds (but other time units may be specified too,
               see systemd.time(7) for supported formats). Defaults to 30s.
               Once the specified timeout elapsed authentication via password
               is attempted. Note that this timeout applies to waiting for
               the security device to show up — it does not apply to the PIN
               prompt for the device (should one be needed) or similar. Pass
               0 to turn off the timeout and wait forever.
    
               Added in version 250.
    
           **try-empty-password=**
               Takes a boolean argument. If enabled, right before asking the
               user for a password it is first attempted to unlock the volume
               with an empty password. This is useful for systems that are
               initialized with an encrypted volume with only an empty
               password set, which shall be replaced with a suitable password
               during first boot, but after activation.
    
               Added in version 246.
    
           **x-systemd.device-timeout=**
               Specifies how long systemd should wait for a block device to
               show up before giving up on the entry. The argument is a time
               in seconds or explicitly specified units of "s", "min", "h",
               "ms".
    
               Added in version 216.
    
           **x-initrd.attach**
               Setup this encrypted block device in the initrd, similarly to
               systemd.mount(5) units marked with **x-initrd.mount**.
    
               Although it is not necessary to mark the mount entry for the
               root file system with **x-initrd.mount** , **x-initrd.attach** is still
               recommended with the encrypted block device containing the
               root file system as otherwise systemd will attempt to detach
               the device during the regular system shutdown while it is
               still in use. With this option the device will still be
               detached but later after the root file system is unmounted.
    
               All other encrypted block devices that contain file systems
               mounted in the initrd should use this option.
    
               Added in version 245.
    
           At early boot and when the system manager configuration is
           reloaded, this file is translated into native systemd units by
           systemd-cryptsetup-generator(8).
    


## AF_UNIX KEY FILES



           If the key file path (as specified in the third column of
           /etc/crypttab entries, see above) refers to an **AF_UNIX** stream
           socket in the file system, the key is acquired by connecting to
           the socket and reading the key from the connection. The connection
           is made from an **AF_UNIX** socket name in the abstract namespace, see
           unix(7) for details. The source socket name is chosen according to
           the following format:
    
               **NUL** _RANDOM_ /cryptsetup/ _VOLUME_
    
           In other words: a **NUL** byte (as required for abstract namespace
           sockets), followed by a random string (consisting of alphanumeric
           characters only), followed by the literal string "/cryptsetup/",
           followed by the name of the volume to acquire they key for. For
           example, for the volume "myvol":
    
               \0d7067f78d9827418/cryptsetup/myvol
    
           Services listening on the **AF_UNIX** stream socket may query the
           source socket name with getpeername(2), and use this to determine
           which key to send, allowing a single listening socket to serve
           keys for multiple volumes. If the PKCS#11 logic is used (see
           above), the socket source name is picked in similar fashion,
           except that the literal string "/cryptsetup-pkcs11/" is used. And
           similarly for FIDO2 ("/cryptsetup-fido2-salt/") and TPM2
           ("/cryptsetup-tpm2/"). A different path component is used so that
           services providing key material know that the secret key was not
           requested directly, but instead an encrypted key that will be
           decrypted via the PKCS#11/FIDO2/TPM2 logic to acquire the final
           secret key.
    


## EXAMPLES



           **Example 1. /etc/crypttab example**
    
           Set up four encrypted block devices. One using LUKS for normal
           storage, another one for usage as a swap device and two TrueCrypt
           volumes. For the fourth device, the option string is interpreted
           as two options "cipher=xchacha12,aes-adiantum-plain64",
           "keyfile-timeout=10s".
    
               luks       UUID=2505567a-9e27-4efe-a4d5-15ad146c258b
               swap       /dev/sda7       /dev/urandom       swap
               truecrypt  /dev/sda2       /etc/container_password  tcrypt
               hidden     /mnt/tc_hidden  /dev/null    tcrypt-hidden,tcrypt-keyfile=/etc/keyfile
               external   /dev/sda3       keyfile:LABEL=keydev keyfile-timeout=10s,cipher=xchacha12\,aes-adiantum-plain64
    
           **Example 2. Yubikey-based PKCS#11 Volume Unlocking Example**
    
           The PKCS#11 logic allows hooking up any compatible security token
           that is capable of storing RSA or EC cryptographic keys for
           unlocking an encrypted volume. Here's an example how to set up a
           Yubikey security token for this purpose on a LUKS2 volume, using
           **ykmap**(1) from the yubikey-manager project to initialize the token
           and systemd-cryptenroll(1) to add it in the LUKS2 volume:
    
               # SPDX-License-Identifier: MIT-0
    
               # Destroy any old key on the Yubikey (careful!)
               ykman piv reset
    
               # Generate a new private/public key pair on the device, store the public key in
               # 'pubkey.pem'.
               ykman piv generate-key -a RSA2048 9d pubkey.pem
    
               # Create a self-signed certificate from this public key, and store it on the
               # device. The "subject" should be an arbitrary user-chosen string to identify
               # the token with.
               ykman piv generate-certificate --subject "Knobelei" 9d pubkey.pem
    
               # We do not need the public key anymore, let's remove it. Since it is not
               # security sensitive we just do a regular "rm" here.
               rm pubkey.pem
    
               # Enroll the freshly initialized security token in the LUKS2 volume. Replace
               # /dev/sdXn by the partition to use (e.g. /dev/sda1).
               sudo systemd-cryptenroll --pkcs11-token-uri=auto /dev/sdXn
    
               # Test: Let's run systemd-cryptsetup to test if this all worked.
               sudo systemd-cryptsetup attach mytest /dev/sdXn none pkcs11-uri=auto
    
               # If that worked, let's now add the same line persistently to /etc/crypttab,
               # for the future. We do not want to use the (unstable) /dev/sdX name, so let's
               # figure out a stable link:
               udevadm info -q symlink -r /dev/sdXn
    
               # Now add the line using the by-uuid symlink to /etc/crypttab:
               sudo bash -c 'echo "mytest /dev/disk/by-uuid/... none pkcs11-uri=auto" >>/etc/crypttab'
    
               # Depending on your distribution and encryption setup, you may need to manually
               # regenerate your initramfs to be able to use a Yubikey / PKCS#11 token to
               # unlock the partition during early boot.
               # More information at https://unix.stackexchange.com/a/705809.
               # On Fedora based systems:
               sudo dracut --force
               # On Debian based systems:
               sudo update-initramfs -u
    
           A few notes on the above:
    
           •   We use RSA2048, which is the longest key size current Yubikeys
               support
    
           •   We use Yubikey key slot 9d, since that's apparently the
               keyslot to use for decryption purposes, see **Yubico PIV**
               **certificate slots******[3].**Example 3. FIDO2 Volume Unlocking Example**
    
           The FIDO2 logic allows using any compatible FIDO2 security token
           that implements the "hmac-secret" extension for unlocking an
           encrypted volume. Here's an example how to set up a FIDO2 security
           token for this purpose for a LUKS2 volume, using
           systemd-cryptenroll(1):
    
               # SPDX-License-Identifier: MIT-0
    
               # Enroll the security token in the LUKS2 volume. Replace /dev/sdXn by the
               # partition to use (e.g. /dev/sda1).
               sudo systemd-cryptenroll --fido2-device=auto /dev/sdXn
    
               # Test: Let's run systemd-cryptsetup to test if this worked.
               sudo systemd-cryptsetup attach mytest /dev/sdXn none fido2-device=auto
    
               # If that worked, let's now add the same line persistently to /etc/crypttab,
               # for the future. We do not want to use the (unstable) /dev/sdX name, so let's
               # figure out a stable link:
               udevadm info -q symlink -r /dev/sdXn
    
               # Now add the line using the by-uuid symlink to /etc/crypttab:
               sudo bash -c 'echo "mytest /dev/disk/by-uuid/... none fido2-device=auto" >>/etc/crypttab'
    
               # Depending on your distribution and encryption setup, you may need to manually
               # regenerate your initramfs to be able to use a FIDO2 device to unlock the
               # partition during early boot.
               # More information at https://unix.stackexchange.com/a/705809.
               # On Fedora based systems:
               sudo dracut --force
               # On Debian based systems:
               sudo update-initramfs -u
    
           **Example 4. TPM2 Volume Unlocking Example**
    
           The TPM2 logic allows using any TPM2 chip supported by the Linux
           kernel for unlocking an encrypted volume. Here's an example how to
           set up a TPM2 chip for this purpose for a LUKS2 volume, using
           systemd-cryptenroll(1):
    
               # SPDX-License-Identifier: MIT-0
    
               # Enroll the TPM2 security chip in the LUKS2 volume, and bind it to PCR 7
               # only. Replace /dev/sdXn by the partition to use (e.g. /dev/sda1).
               sudo systemd-cryptenroll --tpm2-device=auto --tpm2-pcrs=7 /dev/sdXn
    
               # Test: Let's run systemd-cryptsetup to test if this worked.
               sudo systemd-cryptsetup attach mytest /dev/sdXn none tpm2-device=auto
    
               # If that worked, let's now add the same line persistently to /etc/crypttab,
               # for the future. We do not want to use the (unstable) /dev/sdX name, so let's
               # figure out a stable link:
               udevadm info -q symlink -r /dev/sdXn
    
               # Now add the line using the by-uuid symlink to /etc/crypttab:
               sudo bash -c 'echo "mytest /dev/disk/by-uuid/... none tpm2-device=auto" >>/etc/crypttab'
    
               # And now let's check that automatic unlocking works:
               sudo systemd-cryptsetup detach mytest
               sudo systemctl daemon-reload
               sudo systemctl start cryptsetup.target
               systemctl is-active systemd-cryptsetup@mytest.service
    
               # Once we have the device which will be unlocked automatically, we can use it.
               # Usually we would create a file system and add it to /etc/fstab:
               sudo mkfs.ext4 /dev/mapper/mytest
               # This prints a 'Filesystem UUID', which we can use as a stable name:
               sudo bash -c 'echo "/dev/disk/by-uuid/... /var/mytest ext4 defaults,x-systemd.mkdir 0 2" >>/etc/fstab'
               # And now let's check that the mounting works:
               sudo systemctl daemon-reload
               sudo systemctl start /var/mytest
               systemctl status /var/mytest
    
               # Depending on your distribution and encryption setup, you may need to manually
               # regenerate your initramfs to be able to use a TPM2 security chip to unlock
               # the partition during early boot.
               # More information at https://unix.stackexchange.com/a/705809.
               # On Fedora based systems:
               sudo dracut --force
               # On Debian based systems:
               sudo update-initramfs -u
    


## NOTES



            1. Veracrypt Personal Iterations Multiplier
               https://www.veracrypt.fr/en/Personal%20Iterations%20Multiplier%20%28PIM%29.html
    
            2. RFC7512 PKCS#11 URI
               https://tools.ietf.org/html/rfc7512
    
            3. Yubico PIV certificate slots
               https://developers.yubico.com/PIV/Introduction/Certificate_slots.html
    


* * *