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This part of the copyright blurb stems from the GPL use recommendations: https://www.gnu.org/licenses/gpl-howto.en.html The concept appears to originate in times where version control was per file, instead of per tree, and was a way to glue the files together. Ultimately, we nowadays don't live in that world anymore, and this information is entirely useless anyway, as people are very welcome to copy these files into any projects they like, and they shouldn't have to change bits that are part of our copyright header for that. hence, let's just get rid of this old cruft, and shorten our codebase a bit.
172 lines
6.7 KiB
XML
172 lines
6.7 KiB
XML
<?xml version="1.0"?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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Copyright 2011 Lennart Poettering
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-->
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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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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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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>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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