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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>·
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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 215</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="idm214179029408"></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="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="mkswap.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="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="mke2fs.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="idm214174457600"></a><h2 id="Example">Example<a class="headerlink" title="Permalink to this headline" href="#Example">¶</a></h2><div class="example"><a name="idm214174456960"></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="idm214174454576"></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="mkswap.html"><span class="citerefentry"><span class="refentrytitle">mkswap</span>(8)</span></a>,
<a href="mke2fs.html"><span class="citerefentry"><span class="refentrytitle">mke2fs</span>(8)</span></a>
</p></div></div></body></html>
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