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https://github.com/systemd/systemd
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![Zbigniew Jędrzejewski-Szmek](/assets/img/avatar_default.png)
With <para><filename>…</filename></para>, we get a separate "paragraph" for each line, i.e. entries separated by empty lines. This uses up a lot of space and was only done because docbook makes it hard to insert a newline. In some other places, <literallayout> was used, but then we cannot indent the source text (because the whitespace would end up in the final page). We can get the desired result with <simplelist>. With <simplelist> the items are indented in roff output, but not in html output. In some places this looks better then no indentation, and in others it would probably be better to have no indent. But this is a minor issue and we cannot control that. (I didn't convert all spots. There's a bunch of other man pages which have two lines, e.g. an executable and service file, and it doesn't matter there so much.)
196 lines
8.8 KiB
XML
196 lines
8.8 KiB
XML
<?xml version="1.0"?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sysctl.d"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sysctl.d</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sysctl.d</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sysctl.d</refname>
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<refpurpose>Configure kernel parameters at boot</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><simplelist>
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<member><filename>/etc/sysctl.d/*.conf</filename></member>
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<member><filename>/run/sysctl.d/*.conf</filename></member>
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<member><filename>/usr/lib/sysctl.d/*.conf</filename></member>
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</simplelist></para>
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<programlisting>key.name.under.proc.sys = some value
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key/name/under/proc/sys = some value
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key/middle.part.with.dots/foo = 123
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key.middle/part/with/dots.foo = 123
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-key.that.will.not.fail = value
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key.pattern.*.with.glob = whatever
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-key.pattern.excluded.with.glob
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key.pattern.overridden.with.glob = custom
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</programlisting>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>At boot,
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<citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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reads configuration files from the above directories to configure
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<citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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kernel parameters.</para>
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</refsect1>
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<refsect1>
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<title>Configuration Format</title>
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<para>The configuration files contain a list of variable
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assignments, separated by newlines. Empty lines and lines whose
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first non-whitespace character is <literal>#</literal> or
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<literal>;</literal> are ignored.</para>
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<para>Note that either <literal>/</literal> or <literal>.</literal> may be used as separators within
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sysctl variable names. If the first separator is a slash, remaining slashes and dots are left intact. If
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the first separator is a dot, dots and slashes are interchanged.
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<literal>kernel.domainname=foo</literal> and <literal>kernel/domainname=foo</literal> are equivalent and
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will cause <literal>foo</literal> to be written to
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<filename>/proc/sys/kernel/domainname</filename>. Either
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<literal>net.ipv4.conf.enp3s0/200.forwarding</literal> or
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<literal>net/ipv4/conf/enp3s0.200/forwarding</literal> may be used to refer to
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<filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>. A glob
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<citerefentry project='man-pages'><refentrytitle>glob</refentrytitle><manvolnum>7</manvolnum></citerefentry> pattern may be
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used to write the same value to all matching keys. Keys for which an explicit pattern exists will be
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excluded from any glob matching. In addition, a key may be explicitly excluded from being set by any
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matching glob patterns by specifying the key name prefixed with a <literal>-</literal> character and not
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followed by <literal>=</literal>, see SYNOPSIS.</para>
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<para>Any access permission errors and attempts to write variables not present on the local system are
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logged at debug level and do not cause the service to fail. Other types of errors when setting variables
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are logged with higher priority and cause the service to return failure at the end (after processing
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other variables). As an exception, if a variable assignment is prefixed with a single
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<literal>-</literal> character, failure to set the variable for any reason will be logged at debug level
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and will not cause the service to fail.</para>
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<para>The settings configured with <filename>sysctl.d</filename> files will be applied early on boot. The
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network interface-specific options will also be applied individually for each network interface as it
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shows up in the system. (More specifically, <filename>net.ipv4.conf.*</filename>,
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<filename>net.ipv6.conf.*</filename>, <filename>net.ipv4.neigh.*</filename> and
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<filename>net.ipv6.neigh.*</filename>).</para>
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<para>Many sysctl parameters only become available when certain
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kernel modules are loaded. Modules are usually loaded on demand,
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e.g. when certain hardware is plugged in or network brought up.
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This means that
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<citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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which runs during early boot will not configure such parameters if
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they become available after it has run. To set such parameters, it
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is recommended to add an
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<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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rule to set those parameters when they become available.
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Alternatively, a slightly simpler and less efficient option is to
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add the module to
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<citerefentry><refentrytitle>modules-load.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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causing it to be loaded statically before sysctl settings are
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applied (see example below).</para>
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</refsect1>
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<xi:include href="standard-conf.xml" xpointer="confd" />
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<refsect1>
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<title>Examples</title>
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<example>
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<title>Set kernel YP domain name</title>
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<para><filename>/etc/sysctl.d/domain-name.conf</filename>:
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</para>
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<programlisting>kernel.domainname=example.com</programlisting>
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</example>
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<example>
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<title>Apply settings available only when a certain module is loaded (method one)</title>
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<para><filename>/etc/udev/rules.d/99-bridge.rules</filename>:
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</para>
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<programlisting>ACTION=="add", SUBSYSTEM=="module", KERNEL=="br_netfilter", \
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RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge"
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</programlisting>
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<para><filename>/etc/sysctl.d/bridge.conf</filename>:
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</para>
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<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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</programlisting>
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<para>This method applies settings when the module is
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loaded. Please note that, unless the <filename>br_netfilter</filename>
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module is loaded, bridged packets will not be filtered by
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Netfilter (starting with kernel 3.18), so simply not loading the
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module is sufficient to avoid filtering.</para>
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</example>
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<example>
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<title>Apply settings available only when a certain module is loaded (method two)</title>
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<para><filename>/etc/modules-load.d/bridge.conf</filename>:
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</para>
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<programlisting>br_netfilter</programlisting>
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<para><filename>/etc/sysctl.d/bridge.conf</filename>:
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</para>
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<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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</programlisting>
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<para>This method forces the module to be always loaded. Please
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note that, unless the <filename>br_netfilter</filename> module is
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loaded, bridged packets will not be filtered with Netfilter
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(starting with kernel 3.18), so simply not loading the module is
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sufficient to avoid filtering.</para>
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</example>
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<example>
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<title>Set network routing properties for all interfaces</title>
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<para><filename>/etc/sysctl.d/20-rp_filter.conf</filename>:</para>
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<programlisting>net.ipv4.conf.default.rp_filter = 2
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net.ipv4.conf.*.rp_filter = 2
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-net.ipv4.conf.all.rp_filter
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net.ipv4.conf.hub0.rp_filter = 1
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</programlisting>
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<para>The <option>rp_filter</option> key will be set to "2" for all interfaces, except "hub0". We set
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<filename>net.ipv4.conf.default.rp_filter</filename> first, so any interfaces which are added
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<emphasis>later</emphasis> will get this value (this also covers any interfaces detected while we're
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running). The glob matches any interfaces which were detected <emphasis>earlier</emphasis>. The glob
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will also match <filename>net.ipv4.conf.all.rp_filter</filename>, which we don't want to set at all, so
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it is explicitly excluded. And "hub0" is excluded from the glob because it has an explicit setting.
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</para>
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</example>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>modprobe</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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