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73 lines
6.2 KiB
HTML
73 lines
6.2 KiB
HTML
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>machine-id</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="systemd.directives.html">Directives </a>·
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<a href="../python-systemd/index.html">Python </a>·
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<a href="../libudev/index.html">libudev </a>·
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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 204</span><hr><div class="refentry"><a name="machine-id"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>machine-id — Local machine ID configuration file</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><p><code class="filename">/etc/machine-id</code></p></div><div class="refsect1"><a name="idm259782755728"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p>The <code class="filename">/etc/machine-id</code> file
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contains the unique machine id of the local system
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that is set during installation. The machine ID is a
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single newline-terminated, hexadecimal, lowercase 32
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character machine ID string. (When decoded from
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hexadecimal this corresponds with a 16 byte/128 bit
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string.)</p><p>The machine ID is usually generated from a
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random source during system installation and stays
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constant for all subsequent boots. Optionally, for
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stateless systems it is generated during runtime at
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boot if it is found to be empty.</p><p>The machine ID does not change based on user
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configuration, or when hardware is replaced.</p><p>This machine ID adheres to the same format and
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logic as the D-Bus machine ID.</p><p>Programs may use this ID to identify the host
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with a globally unique ID in the network, which does
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not change even if the local network configuration
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changes. Due to this and its greater length it is
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a more useful replacement for the
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<a href="gethostid.html"><span class="citerefentry"><span class="refentrytitle">gethostid</span>(3)</span></a>
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call POSIX specifies.</p><p>The
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<a href="systemd-machine-id-setup.html"><span class="citerefentry"><span class="refentrytitle">systemd-machine-id-setup</span>(1)</span></a>
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tool may be used by installer tools to initialize the
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machine ID at install time.</p></div><div class="refsect1"><a name="idm259782748880"></a><h2 id="Relation to OSF UUIDs">Relation to OSF UUIDs<a class="headerlink" title="Permalink to this headline" href="#Relation%20to%20OSF%20UUIDs">¶</a></h2><p>Note that the machine ID historically is not an
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OSF UUID as defined by <a class="ulink" href="http://tools.ietf.org/html/rfc4122" target="_top">RFC
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4122</a>, nor a Microsoft GUID. Starting with
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systemd v30 newly generated machine IDs however do
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qualify as v4 UUIDs.</p><p>In order to maintain compatibility with existing
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installations, an application requiring a UUID should
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decode the machine ID, and then apply the following
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operations to turn it into a valid OSF v4 UUID. With
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<code class="literal">id</code> being an unsigned character
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array:</p><pre class="programlisting">/* Set UUID version to 4 --- truly random generation */
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id[6] = (id[6] & 0x0F) | 0x40;
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/* Set the UUID variant to DCE */
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id[8] = (id[8] & 0x3F) | 0x80;</pre><p>(This code is inspired by
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<code class="literal">generate_random_uuid()</code> of
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<code class="filename">drivers/char/random.c</code> from the
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kernel sources.)</p></div><div class="refsect1"><a name="idm259782742704"></a><h2 id="History">History<a class="headerlink" title="Permalink to this headline" href="#History">¶</a></h2><p>The simple configuration file format of
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<code class="filename">/etc/machine-id</code> originates in the
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<code class="filename">/var/lib/dbus/machine-id</code> file
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introduced by D-Bus. In fact this latter file might be a
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symlink to
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<code class="varname">/etc/machine-id</code>.</p></div><div class="refsect1"><a name="idm259786693264"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
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<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
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<a href="systemd-machine-id-setup.html"><span class="citerefentry"><span class="refentrytitle">systemd-machine-id-setup</span>(1)</span></a>,
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<a href="gethostid.html"><span class="citerefentry"><span class="refentrytitle">gethostid</span>(3)</span></a>,
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<a href="hostname.html"><span class="citerefentry"><span class="refentrytitle">hostname</span>(5)</span></a>,
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<a href="machine-info.html"><span class="citerefentry"><span class="refentrytitle">machine-info</span>(5)</span></a>,
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<a href="os-release.html"><span class="citerefentry"><span class="refentrytitle">os-release</span>(5)</span></a>,
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<a href="sd-id128.html"><span class="citerefentry"><span class="refentrytitle">sd-id128</span>(3)</span></a>,
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<a href="sd_id128_get_machine.html"><span class="citerefentry"><span class="refentrytitle">sd_id128_get_machine</span>(3)</span></a>
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</p></div></div></body></html>
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