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194 lines
8.7 KiB
XML
194 lines
8.7 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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<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. Moreover, if a variable assignment is
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prefixed with a single <literal>-</literal> character, failure to set the variable for other reasons will
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be logged at debug level and will not cause the service to fail. In other cases, errors when setting
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variables are logged with higher priority and cause the service to return failure at the end (after
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processing other variables).</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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