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+<?xml version="1.0"?>
+<!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!--
+ SPDX-License-Identifier: LGPL-2.1-or-later
+
+ This is based on crypttab(5) from Fedora's initscripts package, which in
+ turn is based on Debian's version.
+
+ The Red Hat version has been written by Miloslav Trmac <mitr@redhat.com>.
+-->
+<refentry id="crypttab" conditional='HAVE_LIBCRYPTSETUP' xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>crypttab</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>crypttab</refentrytitle>
+ <manvolnum>5</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>crypttab</refname>
+ <refpurpose>Configuration for encrypted block devices</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <para><filename>/etc/crypttab</filename></para>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>The <filename>/etc/crypttab</filename> file describes
+ encrypted block devices that are set up during system boot.</para>
+
+ <para>Empty lines and lines starting with the <literal>#</literal>
+ character are ignored. Each of the remaining lines describes one
+ encrypted block device. Fields are delimited by white space.</para>
+
+ <para>Each line is in the form<programlisting><replaceable>volume-name</replaceable> <replaceable>encrypted-device</replaceable> <replaceable>key-file</replaceable> <replaceable>options</replaceable></programlisting>
+ The first two fields are mandatory, the remaining two are
+ optional.</para>
+
+ <para>Setting up encrypted block devices using this file supports four encryption modes: LUKS, TrueCrypt,
+ BitLocker and plain. See <citerefentry
+ project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> 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.</para>
+
+ <para>The four fields of <filename>/etc/crypttab</filename> are defined as follows:</para>
+
+ <orderedlist>
+
+ <listitem><para>The first field contains the name of the resulting volume with decrypted data; its
+ block device is set up below <filename>/dev/mapper/</filename>.</para></listitem>
+
+ <listitem><para>The second field contains a path to the underlying block
+ device or file, or a specification of a block device via
+ <literal>UUID=</literal> followed by the UUID.</para></listitem>
+
+ <listitem><para>The third field specifies an absolute path to a file with the encryption
+ key. Optionally, the path may be followed by <literal>:</literal> and an
+ <filename>/etc/fstab</filename> style device specification (e.g. starting with
+ <literal>LABEL=</literal> 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 <literal>none</literal> or
+ <literal>-</literal>, a key file named after the volume to unlock (i.e. the first column of the line),
+ suffixed with <filename>.key</filename> is automatically loaded from the
+ <filename>/etc/cryptsetup-keys.d/</filename> and <filename>/run/cryptsetup-keys.d/</filename>
+ directories, if present. Otherwise, the password has to be manually entered during system boot. For
+ swap encryption, <filename>/dev/urandom</filename> may be used as key file, resulting in a randomized
+ key.</para>
+
+ <para>If the specified key file path refers to an <constant>AF_UNIX</constant> 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.</para></listitem>
+
+ <listitem><para>The fourth field, if present, is a comma-delimited list of options. The supported
+ options are listed below.</para></listitem>
+ </orderedlist>
+ </refsect1>
+
+ <refsect1>
+ <title>Key Acquisition</title>
+
+ <para>Six different mechanisms for acquiring the decryption key or passphrase unlocking the encrypted
+ volume are supported. Specifically:</para>
+
+ <orderedlist>
+
+ <listitem><para>Most prominently, the user may be queried interactively during volume activation
+ (i.e. typically at boot), asking them to type in the necessary passphrases.</para></listitem>
+
+ <listitem><para>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.</para></listitem>
+
+ <listitem><para>The (unencrypted) key may be requested from another service, by specifying an
+ <constant>AF_UNIX</constant> file system socket in place of a key file in the third field. For details
+ see above and below.</para></listitem>
+
+ <listitem><para>The key may be acquired via a PKCS#11 compatible hardware security token or
+ smartcard. In this case an encrypted key is stored on disk/removable media, acquired via
+ <constant>AF_UNIX</constant>, or stored in the LUKS2 JSON token metadata header. The encrypted key is
+ then decrypted by the PKCS#11 token with an RSA key stored on it, and then used to unlock the encrypted
+ volume. Use the <option>pkcs11-uri=</option> option described below to use this mechanism.</para></listitem>
+
+ <listitem><para>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 <constant>AF_UNIX</constant>, 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 <option>fido2-device=</option> option
+ described below to use this mechanism.</para></listitem>
+
+ <listitem><para>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 <constant>AF_UNIX</constant>, or stored in the
+ LUKS2 JSON token metadata header. Use the <option>tpm2-device=</option> option described below to use
+ this mechanism.</para></listitem>
+ </orderedlist>
+
+ <para>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 <filename>/etc/crypttab</filename> line, but may also
+ configured in <filename>/etc/cryptsetup-keys.d/</filename> and
+ <filename>/run/cryptsetup-keys.d/</filename> (see above) or in the LUKS2 JSON token header (in case of
+ the latter three). Use the
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ tool to enroll PKCS#11, FIDO2 and TPM2 devices in LUKS2 volumes.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Supported Options</title>
+
+ <para>The following options may be used in the fourth field of each line:</para>
+
+ <variablelist class='fstab-options'>
+
+ <varlistentry>
+ <term><option>cipher=</option></term>
+
+ <listitem><para>Specifies the cipher to use. See <citerefentry
+ project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values and the default value of this option. A cipher with unpredictable IV values, such
+ as <literal>aes-cbc-essiv:sha256</literal>, is recommended. Embedded commas in the cipher
+ specification need to be escaped by preceding them with a backslash, see example below.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>discard</option></term>
+
+ <listitem><para>Allow discard requests to be passed through the encrypted block
+ device. This improves performance on SSD storage but has security implications.
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>hash=</option></term>
+
+ <listitem><para>Specifies the hash to use for password
+ hashing. See
+ <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values and the default value of this
+ option.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>header=</option></term>
+
+ <listitem><para>Use a detached (separated) metadata device or
+ file where the LUKS header is stored. This option is only
+ relevant for LUKS devices. See
+ <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values and the default value of this
+ option.</para>
+
+ <para>Optionally, the path may be followed by <literal>:</literal> and an
+ <filename>/etc/fstab</filename> device specification (e.g. starting with <literal>UUID=</literal> 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.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>keyfile-offset=</option></term>
+
+ <listitem><para>Specifies the number of bytes to skip at the
+ start of the key file. See
+ <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values and the default value of this
+ option.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>keyfile-size=</option></term>
+
+ <listitem><para>Specifies the maximum number of bytes to read
+ from the key file. See
+ <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values and the default value of this option. This
+ option is ignored in plain encryption mode, as the key file
+ size is then given by the key size.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>keyfile-erase</option></term>
+
+ <listitem><para>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 <filename>/run/</filename>, generated by a service running before
+ activation), and shall be removed after use. Defaults to off.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>key-slot=</option></term>
+
+ <listitem><para>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
+ <option>luks</option>. See
+ <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values. The default is to try all key slots in
+ sequential order.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>keyfile-timeout=</option></term>
+
+ <listitem><para> 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
+ <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for key files on external devices.
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>luks</option></term>
+
+ <listitem><para>Force LUKS mode. When this mode is used, the
+ following options are ignored since they are provided by the
+ LUKS header on the device: <option>cipher=</option>,
+ <option>hash=</option>,
+ <option>size=</option>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>bitlk</option></term>
+
+ <listitem><para>Decrypt BitLocker drive. Encryption parameters
+ are deduced by cryptsetup from BitLocker header.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>_netdev</option></term>
+
+ <listitem><para>Marks this cryptsetup device as requiring network. It will be
+ started after the network is available, similarly to
+ <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ units marked with <option>_netdev</option>. The service unit to set up this device
+ will be ordered between <filename>remote-fs-pre.target</filename> and
+ <filename>remote-cryptsetup.target</filename>, instead of
+ <filename>cryptsetup-pre.target</filename> and
+ <filename>cryptsetup.target</filename>.</para>
+
+ <para>Hint: if this device is used for a mount point that is specified in
+ <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ the <option>_netdev</option> 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 <filename>local-fs.target</filename>, while the
+ service to configure the network is usually only started <emphasis>after</emphasis>
+ the local file system has been mounted.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>noauto</option></term>
+
+ <listitem><para>This device will not be added to <filename>cryptsetup.target</filename>.
+ 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
+ <option>noauto</option>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>nofail</option></term>
+
+ <listitem><para>This device will not be a hard dependency of
+ <filename>cryptsetup.target</filename>. 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 <option>nofail</option> option, or the boot will fail if the device is not unlocked
+ successfully.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>offset=</option></term>
+
+ <listitem><para>Start offset in the backend device, in 512-byte sectors. This
+ option is only relevant for plain devices.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>plain</option></term>
+
+ <listitem><para>Force plain encryption mode.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>read-only</option></term><term><option>readonly</option></term>
+
+ <listitem><para>Set up the encrypted block device in read-only
+ mode.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>same-cpu-crypt</option></term>
+
+ <listitem><para>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.</para>
+
+ <para>This requires kernel 4.0 or newer.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>submit-from-crypt-cpus</option></term>
+
+ <listitem><para>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.</para>
+
+ <para>This requires kernel 4.0 or newer.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>no-read-workqueue</option></term>
+
+ <listitem><para>Bypass dm-crypt internal workqueue and process read requests synchronously. The
+ default is to queue these requests and process them asynchronously.</para>
+
+ <para>This requires kernel 5.9 or newer.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><option>no-write-workqueue</option></term>
+
+ <listitem><para>Bypass dm-crypt internal workqueue and process write requests synchronously. The
+ default is to queue these requests and process them asynchronously.</para>
+
+ <para>This requires kernel 5.9 or newer.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>skip=</option></term>
+
+ <listitem><para>How many 512-byte sectors of the encrypted data to skip at the
+ beginning. This is different from the <option>offset=</option> option with respect
+ to the sector numbers used in initialization vector (IV) calculation. Using
+ <option>offset=</option> will shift the IV calculation by the same negative
+ amount. Hence, if <option>offset=<replaceable>n</replaceable></option> is given,
+ sector <replaceable>n</replaceable> will get a sector number of 0 for the IV
+ calculation. Using <option>skip=</option> causes sector
+ <replaceable>n</replaceable> to also be the first sector of the mapped device, but
+ with its number for IV generation being <replaceable>n</replaceable>.</para>
+
+ <para>This option is only relevant for plain devices.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>size=</option></term>
+
+ <listitem><para>Specifies the key size in bits. See
+ <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values and the default value of this
+ option.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>sector-size=</option></term>
+
+ <listitem><para>Specifies the sector size in bytes. See
+ <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for possible values and the default value of this
+ option.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>swap</option></term>
+
+ <listitem><para>The encrypted block device will be used as a
+ swap device, and will be formatted accordingly after setting
+ up the encrypted block device, with
+ <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+ This option implies <option>plain</option>.</para>
+
+ <para>WARNING: Using the <option>swap</option> option will
+ destroy the contents of the named partition during every boot,
+ so make sure the underlying block device is specified
+ correctly.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tcrypt</option></term>
+
+ <listitem><para>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:
+ <option>cipher=</option>,
+ <option>hash=</option>,
+ <option>keyfile-offset=</option>,
+ <option>keyfile-size=</option>,
+ <option>size=</option>.</para>
+
+ <para>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.</para>
+
+ <para>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
+ <option>tcrypt-keyfile=</option> to provide the absolute path
+ to all key files. When using an empty passphrase in
+ combination with one or more key files, use
+ <literal>/dev/null</literal> as the password file in the third
+ field.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tcrypt-hidden</option></term>
+
+ <listitem><para>Use the hidden TrueCrypt volume. This option
+ implies <option>tcrypt</option>.</para>
+
+ <para>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
+ <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for more information on this limitation.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tcrypt-keyfile=</option></term>
+
+ <listitem><para>Specifies the absolute path to a key file to
+ use for a TrueCrypt volume. This implies
+ <option>tcrypt</option> and can be used more than once to
+ provide several key files.</para>
+
+ <para>See the entry for <option>tcrypt</option> on the
+ behavior of the passphrase and key files when using TrueCrypt
+ encryption mode.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tcrypt-system</option></term>
+
+ <listitem><para>Use TrueCrypt in system encryption mode. This
+ option implies <option>tcrypt</option>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tcrypt-veracrypt</option></term>
+
+ <listitem><para>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 <option>tcrypt</option>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>timeout=</option></term>
+
+ <listitem><para>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).</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tmp=</option></term>
+
+ <listitem><para>The encrypted block device will be prepared for using it as
+ <filename>/tmp/</filename>; it will be formatted using <citerefentry
+ project='man-pages'><refentrytitle>mkfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Takes
+ a file system type as argument, such as <literal>ext4</literal>, <literal>xfs</literal> or
+ <literal>btrfs</literal>. If no argument is specified defaults to <literal>ext4</literal>. This
+ option implies <option>plain</option>.</para>
+
+ <para>WARNING: Using the <option>tmp</option> option will destroy the contents of the named partition
+ during every boot, so make sure the underlying block device is specified correctly.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tries=</option></term>
+
+ <listitem><para>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.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>headless=</option></term>
+
+ <listitem><para>Takes a boolean argument, defaults to false. If true, never query interactively
+ for the password/PIN. Useful for headless systems.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>verify</option></term>
+
+ <listitem><para>If the encryption password is read from console, it has to be entered twice to
+ prevent typos.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>password-echo=yes|no|masked</option></term>
+
+ <listitem><para>Controls whether to echo passwords or security token PINs
+ that are read from console. Takes a boolean or the special string <literal>masked</literal>.
+ The default is <option>password-echo=masked</option>.</para>
+
+ <para>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 <literal>masked</literal>, an asterisk
+ (<literal>*</literal>) is echoed for each character typed. Regardless of
+ which mode is chosen, if the user hits the tabulator key (<literal>↹</literal>)
+ at any time, or the backspace key (<literal>⌫</literal>) before any other
+ data has been entered, then echo is turned off.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>pkcs11-uri=</option></term>
+
+ <listitem><para>Takes either the special value <literal>auto</literal> or an <ulink
+ url="https://tools.ietf.org/html/rfc7512">RFC7512 PKCS#11 URI</ulink> pointing to a private RSA 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.</para>
+
+ <para>If specified as <literal>auto</literal> 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. Use
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ as simple tool for enrolling PKCS#11 security tokens or smartcards in a way compatible with
+ <literal>auto</literal>. In this mode the third column of the line should remain empty (that is,
+ specified as <literal>-</literal>).</para>
+
+ <para>The specified URI can refer directly to a private RSA key stored on a token or alternatively
+ just to a slot or token, in which case a search for a suitable private RSA key will be performed. In
+ this case if multiple suitable objects are found the token is refused. The encrypted key configured
+ in the third column of the line is passed as is (i.e. in binary form, unprocessed) to RSA
+ decryption. The resulting decrypted key is then Base64 encoded before it is used to unlock the LUKS
+ volume.</para>
+
+ <para>Use <command>systemd-cryptenroll --pkcs11-token-uri=list</command> to list all suitable PKCS#11
+ security tokens currently plugged in, along with their URIs.</para>
+
+ <para>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 <option>fido2-device=</option>
+ (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.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>fido2-device=</option></term>
+
+ <listitem><para>Takes either the special value <literal>auto</literal> or the path to a
+ <literal>hidraw</literal> device node (e.g. <filename>/dev/hidraw1</filename>) referring to a FIDO2
+ security token that implements the <literal>hmac-secret</literal> 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.</para>
+
+ <para>If specified as <literal>auto</literal> the FIDO2 token device is automatically discovered, as
+ it is plugged in.</para>
+
+ <para>FIDO2 volume unlocking requires a client ID hash (CID) to be configured via
+ <option>fido2-cid=</option> (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
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ as simple tool for enrolling FIDO2 security tokens, compatible with this automatic mode, which is
+ only available for LUKS2 volumes.</para>
+
+ <para>Use <command>systemd-cryptenroll --fido2-device=list</command> to list all suitable FIDO2
+ security tokens currently plugged in, along with their device nodes.</para>
+
+ <para>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.</para>
+
+ <para>Note that many security tokens that implement FIDO2 also implement PKCS#11, suitable for
+ unlocking volumes via the <option>pkcs11-uri=</option> option described above. Typically the newer,
+ simpler FIDO2 standard is preferable.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>fido2-cid=</option></term>
+
+ <listitem><para>Takes a Base64 encoded FIDO2 client ID to use for the FIDO2 unlock operation. If
+ specified, but <option>fido2-device=</option> is not, <option>fido2-device=auto</option> is
+ implied. If <option>fido2-device=</option> is used but <option>fido2-cid=</option> is not, the volume
+ must be of LUKS2 type, and the CID is read from the LUKS2 JSON token header. Use
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ for enrolling a FIDO2 token in the LUKS2 header compatible with this automatic
+ mode.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>fido2-rp=</option></term>
+
+ <listitem><para>Takes a string, configuring the FIDO2 Relying Party (rp) for the FIDO2 unlock
+ operation. If not specified <literal>io.systemd.cryptsetup</literal> is used, except if the LUKS2
+ JSON token header contains a different value. It should normally not be necessary to override
+ this.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tpm2-device=</option></term>
+
+ <listitem><para>Takes either the special value <literal>auto</literal> or the path to a device node
+ (e.g. <filename>/dev/tpmrm0</filename>) 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.</para>
+
+ <para>Use <option>tpm2-pcrs=</option> (see below) to configure the set of TPM2 PCRs to bind the
+ volume unlocking to. Use
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ as simple tool for enrolling TPM2 security chips in LUKS2 volumes.</para>
+
+ <para>If specified as <literal>auto</literal> the TPM2 device is automatically discovered. Use
+ <command>systemd-cryptenroll --tpm2-device=list</command> to list all suitable TPM2 devices currently
+ available, along with their device nodes.</para>
+
+ <para>This option implements the following mechanism: when enrolling a TPM2 device via
+ <command>systemd-cryptenroll</command> 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.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tpm2-pcrs=</option></term>
+
+ <listitem><para>Takes a <literal>+</literal> 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
+ <command>systemd-cryptenroll</command> 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.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tpm2-pin=</option></term>
+
+ <listitem><para>Takes a boolean argument, defaults to <literal>false</literal>. 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.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>tpm2-signature=</option></term>
+
+ <listitem><para>Takes an absolute path to a TPM2 PCR JSON signature file, as produced by the
+ <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ 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
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ 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
+ <filename>tpm2-pcr-signature.json</filename> is searched for in <filename>/etc/systemd/</filename>,
+ <filename>/run/systemd/</filename>, <filename>/usr/lib/systemd/</filename> (in this
+ order).</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>token-timeout=</option></term>
+
+ <listitem><para>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 <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ 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 time-out and wait forever.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>try-empty-password=</option></term>
+
+ <listitem><para>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.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>x-systemd.device-timeout=</option></term>
+
+ <listitem><para>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
+ <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>ms</literal>.
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>x-initrd.attach</option></term>
+
+ <listitem><para>Setup this encrypted block device in the initrd, similarly to
+ <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ units marked with <option>x-initrd.mount</option>.</para>
+
+ <para>Although it's not necessary to mark the mount entry for the root file system with
+ <option>x-initrd.mount</option>, <option>x-initrd.attach</option> 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's still in
+ use. With this option the device will still be detached but later after the root file
+ system is unmounted.</para>
+
+ <para>All other encrypted block devices that contain file systems mounted in the initrd should use
+ this option.</para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ <para>At early boot and when the system manager configuration is
+ reloaded, this file is translated into native systemd units by
+ <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
+ </refsect1>
+
+ <refsect1>
+ <title><constant>AF_UNIX</constant> Key Files</title>
+
+ <para>If the key file path (as specified in the third column of <filename>/etc/crypttab</filename>
+ entries, see above) refers to an <constant>AF_UNIX</constant> 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 <constant>AF_UNIX</constant> socket name in the abstract namespace, see <citerefentry
+ project='man-pages'><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
+ details. The source socket name is chosen according the following format:</para>
+
+ <programlisting><constant>NUL</constant> <replaceable>RANDOM</replaceable> /cryptsetup/ <replaceable>VOLUME</replaceable></programlisting>
+
+ <para>In other words: a <constant>NUL</constant> byte (as required for abstract namespace sockets),
+ followed by a random string (consisting of alphanumeric characters only), followed by the literal
+ string <literal>/cryptsetup/</literal>, followed by the name of the volume to acquire they key
+ for. For example, for the volume <literal>myvol</literal>:</para>
+
+ <programlisting>\0d7067f78d9827418/cryptsetup/myvol</programlisting>
+
+ <para>Services listening on the <constant>AF_UNIX</constant> stream socket may query the source socket
+ name with <citerefentry
+ project='man-pages'><refentrytitle>getpeername</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
+ 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 <literal>/cryptsetup-pkcs11/</literal> is used. And similarly for
+ FIDO2 (<literal>/cryptsetup-fido2/</literal>) and TPM2 (<literal>/cryptsetup-tpm2/</literal>). A diffent
+ 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.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Examples</title>
+ <example>
+ <title>/etc/crypttab example</title>
+ <para>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 <literal>cipher=xchacha12,aes-adiantum-plain64</literal>,
+ <literal>keyfile-timeout=10s</literal>.</para>
+
+ <programlisting>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
+</programlisting>
+ </example>
+
+ <example>
+ <title>Yubikey-based PKCS#11 Volume Unlocking Example</title>
+
+ <para>The PKCS#11 logic allows hooking up any compatible security token that is capable of storing RSA
+ decryption 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 <citerefentry
+ project='debian'><refentrytitle>ykmap</refentrytitle><manvolnum>1</manvolnum></citerefentry> from the
+ yubikey-manager project to initialize the token and
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ to add it in the LUKS2 volume:</para>
+
+ <programlisting><xi:include href="yubikey-crypttab.sh" parse="text" /></programlisting>
+
+ <para>A few notes on the above:</para>
+
+ <itemizedlist>
+ <listitem><para>We use RSA2048, which is the longest key size current Yubikeys support</para></listitem>
+ <listitem><para>We use Yubikey key slot 9d, since that's apparently the keyslot to use for decryption purposes,
+ <ulink url="https://developers.yubico.com/PIV/Introduction/Certificate_slots.html">see
+ documentation</ulink>.</para></listitem>
+ </itemizedlist>
+ </example>
+
+ <example>
+ <title>FIDO2 Volume Unlocking Example</title>
+
+ <para>The FIDO2 logic allows using any compatible FIDO2 security token that implements the
+ <literal>hmac-secret</literal> 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
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>:</para>
+
+ <programlisting><xi:include href="fido2-crypttab.sh" parse="text" /></programlisting>
+ </example>
+
+ <example>
+ <title>TPM2 Volume Unlocking Example</title>
+
+ <para>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
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>:</para>
+
+ <programlisting><xi:include href="tpm2-crypttab.sh" parse="text" /></programlisting>
+ </example>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>