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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 218</span><hr><div class="refentry"><a name="sysctl.d"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sysctl.d — Configure kernel parameters at boot</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><p><code class="filename">/etc/sysctl.d/*.conf</code></p><p><code class="filename">/run/sysctl.d/*.conf</code></p><p><code class="filename">/usr/lib/sysctl.d/*.conf</code></p></div><div class="refsect1"><a name="idm140180412205808"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p>At boot,
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<a href="systemd-sysctl.service.html"><span class="citerefentry"><span class="refentrytitle">systemd-sysctl.service</span>(8)</span></a>
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reads configuration files from the above directories
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to configure
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<a href="sysctl.html"><span class="citerefentry"><span class="refentrytitle">sysctl</span>(8)</span></a>
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kernel parameters.</p></div><div class="refsect1"><a name="idm140180416018576"></a><h2 id="Configuration Format">Configuration Format<a class="headerlink" title="Permalink to this headline" href="#Configuration%20Format">¶</a></h2><p>The configuration files contain a list of
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variable assignments, separated by newlines. Empty
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lines and lines whose first non-whitespace character
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is "<code class="literal">#</code>" or "<code class="literal">;</code>" are
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ignored.</p><p>Note that either "<code class="literal">/</code>" or
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"<code class="literal">.</code>" may be used as separators within
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sysctl variable names. If the first separator is a
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slash, remaining slashes and dots are left intact. If
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the first separator is a dot, dots and slashes are
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interchanged. "<code class="literal">kernel.domainname=foo</code>"
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and "<code class="literal">kernel/domainname=foo</code>" are
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equivalent and will cause "<code class="literal">foo</code>" to
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be written to
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<code class="filename">/proc/sys/kernel/domainname</code>.
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Either
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"<code class="literal">net.ipv4.conf.enp3s0/200.forwarding</code>"
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or
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"<code class="literal">net/ipv4/conf/enp3s0.200/forwarding</code>"
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may be used to refer to
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<code class="filename">/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</code>.
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</p><p>The settings configured with
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<code class="filename">sysctl.d</code> files will be applied
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early on boot. The network interface-specific options
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will also be applied individually for each network
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interface as it shows up in the system. (More
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specifically,
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<code class="filename">net.ipv4.conf.*</code>,
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<code class="filename">net.ipv6.conf.*</code>,
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<code class="filename">net.ipv4.neigh.*</code> and <code class="filename">net.ipv6.neigh.*</code>).</p><p>Many sysctl parameters only become available
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when certain kernel modules are loaded. Modules are
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usually loaded on demand, e.g. when certain hardware
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is plugged in or network brought up. This means that
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<a href="systemd-sysctl.service.html"><span class="citerefentry"><span class="refentrytitle">systemd-sysctl.service</span>(8)</span></a> which runs
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during early boot will not configure such parameters
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if they become available after it has run. To
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set such parameters, it is recommended to add
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an <a href="udev.html"><span class="citerefentry"><span class="refentrytitle">udev</span>(7)</span></a> rule to set those parameters when they become
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available. Alternatively, a slightly simpler and
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less efficient option is to add the module to
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<a href="modules-load.d.html"><span class="citerefentry"><span class="refentrytitle">modules-load.d</span>(5)</span></a>, causing it to be loaded statically
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before sysctl settings are applied (see
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example below).</p></div><div class="refsection"><a name="confd"></a><h2>Configuration Directories and Precedence</h2><p>Configuration files are read from directories in
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<code class="filename">/etc/</code>, <code class="filename">/run/</code>, and
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<code class="filename">/usr/lib/</code>, in order of precedence.
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Each configuration file in these configuration directories shall be named in
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the style of <code class="filename"><em class="replaceable"><code>filename</code></em>.conf</code>.
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Files in <code class="filename">/etc/</code> override files with the same name in
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<code class="filename">/run/</code> and <code class="filename">/usr/lib/</code>. Files in
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<code class="filename">/run/</code> override files with the same name in
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<code class="filename">/usr/lib/</code>.</p><p>Packages should install their configuration files in
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<code class="filename">/usr/lib/</code>. Files in <code class="filename">/etc/</code> are
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reserved for the local administrator, who may use this logic to override the
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configuration files installed by vendor packages. All configuration files
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are sorted by their filename in lexicographic order, regardless of which of
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the directories they reside in. If multiple files specify the same option,
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the entry in the file with the lexicographically latest name will take
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precedence. It is recommended to prefix all filenames with a two-digit number
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and a dash, to simplify the ordering of the files.</p><p>If the administrator wants to disable a configuration file supplied by
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the vendor, the recommended way is to place a symlink to
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<code class="filename">/dev/null</code> in the configuration directory in
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<code class="filename">/etc/</code>, with the same filename as the vendor
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configuration file.</p></div><div class="refsect1"><a name="idm140180416148912"></a><h2 id="Examples">Examples<a class="headerlink" title="Permalink to this headline" href="#Examples">¶</a></h2><div class="example"><a name="idm140180416148240"></a><p class="title"><b>Example 1. Set kernel YP domain name</b></p><div class="example-contents"><p><code class="filename">/etc/sysctl.d/domain-name.conf</code>:
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</p><pre class="programlisting">kernel.domainname=example.com</pre></div></div><br class="example-break"><div class="example"><a name="idm140180416145664"></a><p class="title"><b>Example 2. Disable packet filter on bridged packets (method one)</b></p><div class="example-contents"><p><code class="filename">/etc/udev/rules.d/99-bridge.rules</code>:
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</p><pre class="programlisting">ACTION=="add", SUBSYSTEM=="module", KERNEL=="bridge", RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge"
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</pre><p><code class="filename">/etc/sysctl.d/bridge.conf</code>:
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</p><pre class="programlisting">net.bridge.bridge-nf-call-ip6tables = 0
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net.bridge.bridge-nf-call-iptables = 0
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net.bridge.bridge-nf-call-arptables = 0
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</pre></div></div><br class="example-break"><div class="example"><a name="idm140180416141312"></a><p class="title"><b>Example 3. Disable packet filter on bridged packets (method two)</b></p><div class="example-contents"><p><code class="filename">/etc/modules-load.d/bridge.conf</code>:
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</p><pre class="programlisting">bridge</pre><p><code class="filename">/etc/sysctl.d/bridge.conf</code>:
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</p><pre class="programlisting">net.bridge.bridge-nf-call-ip6tables = 0
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net.bridge.bridge-nf-call-iptables = 0
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net.bridge.bridge-nf-call-arptables = 0
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</pre></div></div><br class="example-break"></div><div class="refsect1"><a name="idm140180416136928"></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-sysctl.service.html"><span class="citerefentry"><span class="refentrytitle">systemd-sysctl.service</span>(8)</span></a>,
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<a href="systemd-delta.html"><span class="citerefentry"><span class="refentrytitle">systemd-delta</span>(1)</span></a>,
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<a href="sysctl.html"><span class="citerefentry"><span class="refentrytitle">sysctl</span>(8)</span></a>,
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<a href="sysctl.conf.html"><span class="citerefentry"><span class="refentrytitle">sysctl.conf</span>(5)</span></a>,
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<a href="modprobe.html"><span class="citerefentry"><span class="refentrytitle">modprobe</span>(8)</span></a>
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</p></div></div></body></html>
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