203 lines
9.6 KiB
XML
203 lines
9.6 KiB
XML
<?xml version="1.0"?>
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<!--*-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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This file is part of systemd.
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Copyright 2011 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sysctl.d">
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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
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to configure
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<citerefentry><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
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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 <literal>#</literal> or <literal>;</literal> are
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ignored.</para>
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<para>Each configuration file shall be named in the
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style of <filename><replaceable>program</replaceable>.conf</filename>.
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Files in <filename>/etc/</filename> override files
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with the same name in <filename>/usr/lib/</filename>
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and <filename>/run/</filename>. Files in
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<filename>/run/</filename> override files with the same
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name in <filename>/usr/lib/</filename>. Packages
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should install their configuration files in
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<filename>/usr/lib/</filename>. Files in
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<filename>/etc/</filename> are reserved for the local
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administrator, who may use this logic to override the
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configuration files installed by vendor packages. All
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configuration files are sorted by their filename in
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lexicographic order, regardless of which of the
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directories they reside in. If multiple files specify the
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same variable name, the entry in the file with the
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lexicographically latest name will be applied. It is
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recommended to prefix all filenames with a two-digit
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number and a dash, to simplify the ordering of the
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files.</para>
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<para>Note that either <literal>/</literal> or
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<literal>.</literal> 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. <literal>kernel.domainname=foo</literal>
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and <literal>kernel/domainname=foo</literal> are
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equivalent and will cause <literal>foo</literal> to
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be written to
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<filename>/proc/sys/kernel/domainname</filename>.
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Either
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<literal>net.ipv4.conf.enp3s0/200.forwarding</literal>
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or
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<literal>net/ipv4/conf/enp3s0.200/forwarding</literal>
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may be used 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>If the administrator wants to disable a
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configuration file supplied by the vendor, the
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recommended way is to place a symlink to
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<filename>/dev/null</filename> in
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<filename>/etc/sysctl.d/</filename> bearing the
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same filename.</para>
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<para>The settings configured with
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<filename>sysctl.d</filename> 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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<filename>net.ipv4.conf.*</filename>,
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<filename>net.ipv6.conf.*</filename>,
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<filename>net.ipv4.neigh.*</filename> and <filename>net.ipv6.neigh.*</filename>).</para>
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<para>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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<citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> 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 <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> 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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<citerefentry><refentrytitle>modules-load.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>, causing it to be loaded statically
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before sysctl settings are applied (see
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example below).</para>
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</refsect1>
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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>Disable packet filter on bridged packets (method one)</title>
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<para><filename>/etc/udev/rules.d/99-bridge.conf</filename>:
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</para>
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<programlisting>ACTION=="add", SUBSYSTEM=="module", KERNEL=="bridge", RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/proc/sys/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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</example>
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<example>
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<title>Disable packet filter on bridged packets (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>bridge</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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</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><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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<citerefentry><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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