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man: document /etc/crypttab
2012-06-27 15:23:12 +04:00
<?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">
<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 #
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>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 a specification of a block
device via <literal>UUID=</literal> followed by the
UUID. If the block device contains a LUKS signature,
it is opened as a LUKS encrypted partition; otherwise
it is assumed to be a raw dm-crypt partition.</para>
<para>The third field specifies the encryption
password. If the field is not present or the password
is set to none, the password has to be manually
entered during system boot. Otherwise the field is
interpreted as a 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>
<varlistentry>
<term><varname>cipher=</varname></term>
<listitem><para>Specifies the cipher
to use; see
<citerefentry><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><varname>size=</varname></term>
<listitem><para>Specifies the key size
in bits; see
<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for possible values and the default
value of this
option. </para></listitem>
</varlistentry>
cryptsetup: add keyfile-size= support This is useful e.g. if the keyfile is a raw device, where only parts of it should be read. It is typically used whenever the keyfile-offset= option is specified. Tested-by: Erik Westrup <erik.westrup@gmail.com>
2012-08-03 14:47:24 +04:00
<varlistentry>
<term><varname>keyfile-size=</varname></term>
<listitem><para>Specifies the maximum number
of bytes to read from the keyfile; see
<citerefentry><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 keyfile-size is then given by the key size.</para></listitem>
</varlistentry>
cryptsetup: add keyfile-offset= support This is useful if your keyfile is a block device, and you want to use a specific part of it, such as an area between the MBR and the first partition. This feature is documented in the Arch wiki[0], and has been supported by the Arch initscripts, so would be nice to get this into systemd. This requires libcryptsetup >= 1.4.2 (released 12.4.2012). Acked-by: Paul Menzel <paulepanter@users.sourceforge.net> [0]: <https://wiki.archlinux.org/index.php/System_Encryption_with_LUKS# Storing_the_key_between_MBR_and_1st_partition>
2012-06-29 16:36:37 +04:00
<varlistentry>
<term><varname>keyfile-offset=</varname></term>
<listitem><para>Specifies the number
of bytes to skip at the start of
the keyfile; see
<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for possible values and the default
value of this option.</para></listitem>
</varlistentry>
man: document /etc/crypttab
2012-06-27 15:23:12 +04:00
<varlistentry>
<term><varname>hash=</varname></term>
<listitem><para>Specifies the hash to
use for password hashing; see
<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> for possible values and
the default value of this
option. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>tries=</varname></term>
<listitem><para>Specifies the maximum
number of times the user is queried
for a password.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>verify</varname></term>
man: fix a bunch of typos in docs https://bugs.freedesktop.org/show_bug.cgi?id=54501
2012-09-04 21:24:16 +04:00
<listitem><para> If the encryption
man: document /etc/crypttab
2012-06-27 15:23:12 +04:00
password is read from console, it has
to be entered twice (to prevent
typos). </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>read-only</varname></term>
<listitem><para>Set up the encrypted
block device in read-only
mode.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>allow-discards</varname></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><varname>luks</varname></term>
<listitem><para>Force LUKS mode.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>plain</varname></term>
<listitem><para>Force plain encryption
mode.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>timeout=</varname></term>
<listitem><para>Specify the timeout
man: fix a bunch of typos in docs https://bugs.freedesktop.org/show_bug.cgi?id=54501
2012-09-04 21:24:16 +04:00
for querying for a password. If no
unit is specified seconds is used.
Supported units are s, ms,
man: document /etc/crypttab
2012-06-27 15:23:12 +04:00
us, min, h, d.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>noauto</varname></term>
<listitem><para> This device will not
be automatically unlocked on
boot. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>nofail</varname></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 doesn't show
up.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>swap</varname></term>
<listitem><para> The encrypted block
device will be used as a swap
partition, and will be formatted as a
swap partition after setting up the
encrypted block device, with
<citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
<para>WARNING: Using the
<varname>swap</varname> 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><varname>tmp</varname></term>
<listitem><para>The encrypted block
device will be prepared for using it
as <filename>/tmp</filename>
partition: it will be formatted using
<citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
<para>WARNING: Using the
<varname>tmp</varname> 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>
</variablelist>
man: document systemd-cryptsetup-generator
2012-06-27 16:51:47 +04:00
<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>
man: document /etc/crypttab
2012-06-27 15:23:12 +04:00
</refsect1>
<refsect1>
<title>Example</title>
<example>
<title>/etc/crypttab example</title>
<para>Set up two encrypted block devices with
LUKS: one normal one for storage, and another
one for usage as swap device.</para>
<programlisting>luks-2505567a-9e27-4efe-a4d5-15ad146c258b UUID=2505567a-9e27-4efe-a4d5-15ad146c258b - timeout=0
swap /dev/sda7 /dev/urandom swap</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>,
man: document systemd-cryptsetup-generator
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<citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
man: document /etc/crypttab
2012-06-27 15:23:12 +04:00
<citerefentry><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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