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diff --git a/man/crypttab.xml b/man/crypttab.xml new file mode 100644 index 0000000..0519242 --- /dev/null +++ b/man/crypttab.xml @@ -0,0 +1,575 @@ +<?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 + three encryption modes: LUKS, TrueCrypt 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 first field contains the name of the resulting encrypted volume; its block device is set up + below <filename>/dev/mapper/</filename>.</para> + + <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> + + <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 fstab device specification (e.g. starting with + <literal>LABEL=</literal> or similar); in which case the path is taken relative to the device 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.</para> + + <para>The fourth field, if present, is a comma-delimited list of + options. The following options are recognized:</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 fstab 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 and falls back to a password if + it could not be mounted. 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>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>pkcs11-uri=</option></term> + + <listitem><para>Takes a <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 key specified in the third column of the + line. This is useful for unlocking encrypted volumes through security tokens or smartcards. See below + for an example how to set up this mechanism for unlocking a LUKS volume with a YubiKey security + token. 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 key configured in the + third column is passed as is to RSA decryption. The resulting decrypted key is then base64 encoded + before it is used to unlock the LUKS volume.</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 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 initramfs, 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 initramfs + 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>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 Volume Unlocking Example</title> + + <para>The PKCS#11 logic allows hooking up any compatible security token that is capable of storing RSA + decryption keys. Here's an example how to set up a Yubikey security token for this purpose, using + <citerefentry project='debian'><refentrytitle>ykmap</refentrytitle><manvolnum>1</manvolnum></citerefentry> + from the yubikey-manager project:</para> + +<programlisting><xi:include href="yubikey-crypttab.sh" parse="text" /></programlisting> + +<para>A few notes on the above:</para> + +<itemizedlist> + <listitem><para>We use RSA (and not ECC), since Yubikeys support PKCS#11 Decrypt() only for RSA keys</para></listitem> + <listitem><para>We use RSA2048, which is the longest key size current Yubikeys support</para></listitem> + <listitem><para>LUKS key size must be shorter than 2048bit due to RSA padding, hence we use 128 bytes</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> + </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 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> |