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systemd/man/crypttab.xml
Lukas Nykryn 517dcac840 Revert "man: suggest using hash= atribut for swap in example" 
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<?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><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='crypttab-options'>
<varlistentry>
<term><varname>discard</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>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>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>keyfile-offset=</varname></term>
<listitem><para>Specifies the number of bytes to
skip at the start of the key file. 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>keyfile-size=</varname></term>
<listitem><para>Specifies the maximum number
of bytes to read from the key file. 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 key file size is then
given by the key size.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>luks</varname></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: <varname>cipher=</varname>,
<varname>hash=</varname>,
<varname>size=</varname>.</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 does not show up.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>plain</varname></term>
<listitem><para>Force plain encryption mode.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>read-only</varname></term><term><varname>readonly</varname></term>
<listitem><para>Set up the encrypted block
device in read-only mode.</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>
<varlistentry>
<term><varname>swap</varname></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><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
This option implies <varname>plain</varname>.</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>tcrypt</varname></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:
<varname>cipher=</varname>,
<varname>hash=</varname>,
<varname>keyfile-offset=</varname>,
<varname>keyfile-size=</varname>,
<varname>size=</varname>.</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
<varname>tcrypt-keyfile=</varname> 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><varname>tcrypt-hidden</varname></term>
<listitem><para>Use the hidden TrueCrypt volume.
This implies <varname>tcrypt</varname>.</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><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for more information on this limitation.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>tcrypt-keyfile=</varname></term>
<listitem><para>Specifies the absolute path to a
key file to use for a TrueCrypt volume. This
implies <varname>tcrypt</varname> and can be
used more than once to provide several key
files.</para>
<para>See the entry for <varname>tcrypt</varname>
on the behavior of the passphrase and key files
when using TrueCrypt encryption mode.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>tcrypt-system</varname></term>
<listitem><para>Use TrueCrypt in system
encryption mode. This implies
<varname>tcrypt</varname>.</para>
<para>Please note that when using this mode, the
whole device needs to be given in the second
field instead of the partition. For example: if
<literal>/dev/sda2</literal> is the system
encrypted TrueCrypt patition, <literal>/dev/sda</literal>
has to be given.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>timeout=</varname></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><varname>tmp</varname></term>
<listitem><para>The encrypted block device will
be prepared for using it as <filename>/tmp</filename>;
it will be formatted using
<citerefentry><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
This option implies <varname>plain</varname>.</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>
<varlistentry>
<term><varname>tries=</varname></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><varname>verify</varname></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 /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><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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