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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>crypttab</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><style>
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</style><a href="index.html">Index </a>·
<a href="systemd.directives.html">Directives </a>·
<a href="../python-systemd/index.html">Python </a>·
<a href="../libudev/index.html">libudev </a>·
<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 219</span><hr><div class="refentry"><a name="crypttab"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>crypttab — Configuration for encrypted block devices</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><p><code class="filename">/etc/crypttab</code></p></div><div class="refsect1"><a name="idm140688860579392"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description"></a></h2><p>The <code class="filename">/etc/crypttab</code> file describes
encrypted block devices that are set up during system boot.</p><p>Empty lines and lines starting with the "<code class="literal">#</code>"
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.</p><p>Setting up encrypted block devices using this file supports
three encryption modes: LUKS, TrueCrypt and plain. See
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>
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.</p><p>The first field contains the name of the resulting encrypted
block device; the device is set up within
<code class="filename">/dev/mapper/</code>.</p><p>The second field contains a path to the underlying block
device or file, or a specification of a block device via
"<code class="literal">UUID=</code>" followed by the UUID.</p><p>The third field specifies the encryption password. If the
field is not present or the password is set to
"<code class="literal">none</code>" or "<code class="literal">-</code>", 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, <code class="filename">/dev/urandom</code>
or the hardware device <code class="filename">/dev/hw_random</code> can be
used as the password file; using <code class="filename">/dev/random</code>
may prevent boot completion if the system does not have enough
entropy to generate a truly random encryption key.</p><p>The fourth field, if present, is a comma-delimited list of
options. The following options are recognized:</p><div class="variablelist"><dl class="variablelist"><dt id="discard"><span class="term"><code class="option">discard</code></span><a class="headerlink" title="Permalink to this term" href="#discard"></a></dt><dd><p>Allow discard requests to be passed through
the encrypted block device. This improves performance on SSD
storage but has security implications.</p></dd><dt id="cipher="><span class="term"><code class="option">cipher=</code></span><a class="headerlink" title="Permalink to this term" href="#cipher="></a></dt><dd><p>Specifies the cipher to use. See
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>
for possible values and the default value of this option. A
cipher with unpredictable IV values, such as
"<code class="literal">aes-cbc-essiv:sha256</code>", is
recommended.</p></dd><dt id="hash="><span class="term"><code class="option">hash=</code></span><a class="headerlink" title="Permalink to this term" href="#hash="></a></dt><dd><p>Specifies the hash to use for password
hashing. See
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>
for possible values and the default value of this
option.</p></dd><dt id="header="><span class="term"><code class="option">header=</code></span><a class="headerlink" title="Permalink to this term" href="#header="></a></dt><dd><p>Use a detached (separated) metadata device or
file where the LUKS header is stored. This option is only
relevant for LUKS devices. See
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>
for possible values and the default value of this
option.</p></dd><dt id="keyfile-offset="><span class="term"><code class="option">keyfile-offset=</code></span><a class="headerlink" title="Permalink to this term" href="#keyfile-offset="></a></dt><dd><p>Specifies the number of bytes to skip at the
start of the key file. See
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>
for possible values and the default value of this
option.</p></dd><dt id="keyfile-size="><span class="term"><code class="option">keyfile-size=</code></span><a class="headerlink" title="Permalink to this term" href="#keyfile-size="></a></dt><dd><p>Specifies the maximum number of bytes to read
from the key file. See
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>
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.</p></dd><dt id="key-slot="><span class="term"><code class="option">key-slot=</code></span><a class="headerlink" title="Permalink to this term" href="#key-slot="></a></dt><dd><p>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
<code class="option">luks</code>. See
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>
for possible values. The default is to try all key slots in
sequential order.</p></dd><dt id="luks"><span class="term"><code class="option">luks</code></span><a class="headerlink" title="Permalink to this term" href="#luks"></a></dt><dd><p>Force LUKS mode. When this mode is used, the
following options are ignored since they are provided by the
LUKS header on the device: <code class="option">cipher=</code>,
<code class="option">hash=</code>,
<code class="option">size=</code>.</p></dd><dt id="noauto"><span class="term"><code class="option">noauto</code></span><a class="headerlink" title="Permalink to this term" href="#noauto"></a></dt><dd><p>This device will not be automatically unlocked
on boot.</p></dd><dt id="nofail"><span class="term"><code class="option">nofail</code></span><a class="headerlink" title="Permalink to this term" href="#nofail"></a></dt><dd><p>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.</p></dd><dt id="plain"><span class="term"><code class="option">plain</code></span><a class="headerlink" title="Permalink to this term" href="#plain"></a></dt><dd><p>Force plain encryption mode.</p></dd><dt id="read-only"><span class="term"><code class="option">read-only</code>, </span><span class="term"><code class="option">readonly</code></span><a class="headerlink" title="Permalink to this term" href="#read-only"></a></dt><dd><p>Set up the encrypted block device in read-only
mode.</p></dd><dt id="size="><span class="term"><code class="option">size=</code></span><a class="headerlink" title="Permalink to this term" href="#size="></a></dt><dd><p>Specifies the key size in bits. See
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>
for possible values and the default value of this
option.</p></dd><dt id="swap"><span class="term"><code class="option">swap</code></span><a class="headerlink" title="Permalink to this term" href="#swap"></a></dt><dd><p>The encrypted block device will be used as a
swap device, and will be formatted accordingly after setting
up the encrypted block device, with
<a href="http://man7.org/linux/man-pages/man8/mkswap.8.html"><span class="citerefentry"><span class="refentrytitle">mkswap</span>(8)</span></a>.
This option implies <code class="option">plain</code>.</p><p>WARNING: Using the <code class="option">swap</code> option will
destroy the contents of the named partition during every boot,
so make sure the underlying block device is specified
correctly.</p></dd><dt id="tcrypt"><span class="term"><code class="option">tcrypt</code></span><a class="headerlink" title="Permalink to this term" href="#tcrypt"></a></dt><dd><p>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:
<code class="option">cipher=</code>,
<code class="option">hash=</code>,
<code class="option">keyfile-offset=</code>,
<code class="option">keyfile-size=</code>,
<code class="option">size=</code>.</p><p>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.</p><p>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
<code class="option">tcrypt-keyfile=</code> to provide the absolute path
to all key files. When using an empty passphrase in
combination with one or more key files, use
"<code class="literal">/dev/null</code>" as the password file in the third
field.</p></dd><dt id="tcrypt-hidden"><span class="term"><code class="option">tcrypt-hidden</code></span><a class="headerlink" title="Permalink to this term" href="#tcrypt-hidden"></a></dt><dd><p>Use the hidden TrueCrypt volume. This option
implies <code class="option">tcrypt</code>.</p><p>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
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>
for more information on this limitation.</p></dd><dt id="tcrypt-keyfile="><span class="term"><code class="option">tcrypt-keyfile=</code></span><a class="headerlink" title="Permalink to this term" href="#tcrypt-keyfile="></a></dt><dd><p>Specifies the absolute path to a key file to
use for a TrueCrypt volume. This implies
<code class="option">tcrypt</code> and can be used more than once to
provide several key files.</p><p>See the entry for <code class="option">tcrypt</code> on the
behavior of the passphrase and key files when using TrueCrypt
encryption mode.</p></dd><dt id="tcrypt-system"><span class="term"><code class="option">tcrypt-system</code></span><a class="headerlink" title="Permalink to this term" href="#tcrypt-system"></a></dt><dd><p>Use TrueCrypt in system encryption mode. This
option implies <code class="option">tcrypt</code>.</p></dd><dt id="timeout="><span class="term"><code class="option">timeout=</code></span><a class="headerlink" title="Permalink to this term" href="#timeout="></a></dt><dd><p>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).</p></dd><dt id="x-systemd.device-timeout="><span class="term"><code class="option">x-systemd.device-timeout=</code></span><a class="headerlink" title="Permalink to this term" href="#x-systemd.device-timeout="></a></dt><dd><p>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
"<code class="literal">s</code>",
"<code class="literal">min</code>",
"<code class="literal">h</code>",
"<code class="literal">ms</code>".
</p></dd><dt id="tmp"><span class="term"><code class="option">tmp</code></span><a class="headerlink" title="Permalink to this term" href="#tmp"></a></dt><dd><p>The encrypted block device will be prepared
for using it as <code class="filename">/tmp</code>; it will be
formatted using
<a href="http://man7.org/linux/man-pages/man8/mke2fs.8.html"><span class="citerefentry"><span class="refentrytitle">mke2fs</span>(8)</span></a>.
This option implies <code class="option">plain</code>.</p><p>WARNING: Using the <code class="option">tmp</code> option will
destroy the contents of the named partition during every boot,
so make sure the underlying block device is specified
correctly.</p></dd><dt id="tries="><span class="term"><code class="option">tries=</code></span><a class="headerlink" title="Permalink to this term" href="#tries="></a></dt><dd><p>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.</p></dd><dt id="verify"><span class="term"><code class="option">verify</code></span><a class="headerlink" title="Permalink to this term" href="#verify"></a></dt><dd><p> If the encryption password is read from
console, it has to be entered twice to prevent
typos.</p></dd></dl></div><p>At early boot and when the system manager configuration is
reloaded, this file is translated into native systemd units by
<a href="systemd-cryptsetup-generator.html"><span class="citerefentry"><span class="refentrytitle">systemd-cryptsetup-generator</span>(8)</span></a>.</p></div><div class="refsect1"><a name="idm140688859486096"></a><h2 id="Example">Example<a class="headerlink" title="Permalink to this headline" href="#Example"></a></h2><div class="example"><a name="idm140688859485456"></a><p class="title"><b>Example 1. /etc/crypttab example</b></p><div class="example-contents"><p>Set up four encrypted block devices. One using LUKS for
normal storage, another one for usage as a swap device and two
TrueCrypt volumes.</p><pre class="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</pre></div></div><br class="example-break"></div><div class="refsect1"><a name="idm140688859483136"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also"></a></h2><p>
<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
<a href="systemd-cryptsetup@.service.html"><span class="citerefentry"><span class="refentrytitle">systemd-cryptsetup@.service</span>(8)</span></a>,
<a href="systemd-cryptsetup-generator.html"><span class="citerefentry"><span class="refentrytitle">systemd-cryptsetup-generator</span>(8)</span></a>,
<a href="cryptsetup.html"><span class="citerefentry"><span class="refentrytitle">cryptsetup</span>(8)</span></a>,
<a href="http://man7.org/linux/man-pages/man8/mkswap.8.html"><span class="citerefentry"><span class="refentrytitle">mkswap</span>(8)</span></a>,
<a href="http://man7.org/linux/man-pages/man8/mke2fs.8.html"><span class="citerefentry"><span class="refentrytitle">mke2fs</span>(8)</span></a>
</p></div></div></body></html>
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