| <?xml version="1.0"?> |
| <!--*-nxml-*--> |
| <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
| <!-- |
| This file is part of systemd. |
| |
| Copyright 2012 Lennart Poettering |
| |
| systemd is free software; you can redistribute it and/or modify it |
| under the terms of the GNU Lesser General Public License as published by |
| the Free Software Foundation; either version 2.1 of the License, or |
| (at your option) any later version. |
| |
| systemd is distributed in the hope that it will be useful, but |
| WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public License |
| along with systemd; If not, see <http://www.gnu.org/licenses/>. |
| |
| 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'> |
| |
| <refentryinfo> |
| <title>crypttab</title> |
| <productname>systemd</productname> |
| |
| <authorgroup> |
| <author> |
| <contrib>Documentation</contrib> |
| <firstname>Miloslav</firstname> |
| <surname>Trmac</surname> |
| <email>mitr@redhat.com</email> |
| </author> |
| <author> |
| <contrib>Documentation</contrib> |
| <firstname>Lennart</firstname> |
| <surname>Poettering</surname> |
| <email>lennart@poettering.net</email> |
| </author> |
| </authorgroup> |
| </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 on the line are delimited by white |
| space. 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 |
| block device; the device is set up within |
| <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 the encryption password. If the |
| field is not present or the password is set to |
| <literal>none</literal> or <literal>-</literal>, the password has |
| to be manually entered during system boot. Otherwise, the field is |
| interpreted as a absolute path to a file containing the encryption |
| password. For swap encryption, <filename>/dev/urandom</filename> |
| or the hardware device <filename>/dev/hw_random</filename> can be |
| used as the password file; using <filename>/dev/random</filename> |
| may prevent boot completion if the system does not have enough |
| entropy to generate a truly random encryption key.</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>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>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.</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></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>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 n</option> is given, |
| sector n will get a sector number of 0 for the IV calculation. |
| Using <option>--skip</option> causes sector n to also be the first |
| sector of the mapped device, but with its number for IV generation being n.</para> |
| |
| <para>This option is only relevant for plain devices.</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>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>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>noauto</option></term> |
| |
| <listitem><para>This device will not be automatically unlocked |
| on boot.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>nofail</option></term> |
| |
| <listitem><para>The system will not wait for the device to |
| show up and be unlocked at boot, and not fail the boot if it |
| does not show up.</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>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>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>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>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>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>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>. |
| 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> |
| |
| </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>Example</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.</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</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 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> |