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166 lines
6.9 KiB
XML
166 lines
6.9 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+ -->
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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><filename>/etc/sysctl.d/*.conf</filename></para>
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<para><filename>/run/sysctl.d/*.conf</filename></para>
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<para><filename>/usr/lib/sysctl.d/*.conf</filename></para>
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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
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<literal>.</literal> may be used as separators within sysctl
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variable names. If the first separator is a slash, remaining
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slashes and dots are left intact. If the first separator is a dot,
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dots and slashes are interchanged.
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<literal>kernel.domainname=foo</literal> and
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<literal>kernel/domainname=foo</literal> are equivalent and will
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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
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to refer to
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<filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>.
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</para>
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<para>Any access permission errors and attempts to write variables not defined on the local system are
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logged, but do not cause the the service to fail. Moreover, if a variable assignment is prefixed with a
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single <literal>-</literal> character, failure to set the variable will be logged, but will not cause the
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service to fail. All other errors when setting variables cause the service to return failure at the end
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(other variables are still processed).</para>
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<para>The settings configured with <filename>sysctl.d</filename>
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files will be applied early on boot. The network
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interface-specific options will also be applied individually for
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each network interface as it shows up in the system. (More
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specifically, <filename>net.ipv4.conf.*</filename>,
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<filename>net.ipv6.conf.*</filename>,
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<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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</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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