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3802a3d3 | 1 | <?xml version="1.0"?> <!--*-nxml-*--> |
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2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
d3fae78f | 5 | <refentry id="sysctl.d" |
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6 | xmlns:xi="http://www.w3.org/2001/XInclude"> |
7 | ||
8 | <refentryinfo> | |
9 | <title>sysctl.d</title> | |
10 | <productname>systemd</productname> | |
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11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sysctl.d</refentrytitle> | |
15 | <manvolnum>5</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sysctl.d</refname> | |
20 | <refpurpose>Configure kernel parameters at boot</refpurpose> | |
21 | </refnamediv> | |
22 | ||
23 | <refsynopsisdiv> | |
24 | <para><filename>/etc/sysctl.d/*.conf</filename></para> | |
25 | <para><filename>/run/sysctl.d/*.conf</filename></para> | |
26 | <para><filename>/usr/lib/sysctl.d/*.conf</filename></para> | |
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27 | |
28 | <programlisting>key.name.under.proc.sys = some value | |
29 | key/name/under/proc/sys = some value | |
30 | key/middle.part.with.dots/foo = 123 | |
31 | key.middle/part/with/dots.foo = 123 | |
32 | -key.that.will.not.fail = value | |
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33 | key.pattern.*.with.glob = whatever |
34 | -key.pattern.excluded.with.glob | |
f52b9131 | 35 | key.pattern.overridden.with.glob = custom |
02d89f9a | 36 | </programlisting> |
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37 | </refsynopsisdiv> |
38 | ||
39 | <refsect1> | |
40 | <title>Description</title> | |
41 | ||
42 | <para>At boot, | |
43 | <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> | |
44 | reads configuration files from the above directories to configure | |
3ba3a79d | 45 | <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
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46 | kernel parameters.</para> |
47 | </refsect1> | |
48 | ||
49 | <refsect1> | |
50 | <title>Configuration Format</title> | |
51 | ||
52 | <para>The configuration files contain a list of variable | |
53 | assignments, separated by newlines. Empty lines and lines whose | |
54 | first non-whitespace character is <literal>#</literal> or | |
55 | <literal>;</literal> are ignored.</para> | |
56 | ||
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57 | <para>Note that either <literal>/</literal> or <literal>.</literal> may be used as separators within |
58 | sysctl variable names. If the first separator is a slash, remaining slashes and dots are left intact. If | |
59 | the first separator is a dot, dots and slashes are interchanged. | |
60 | <literal>kernel.domainname=foo</literal> and <literal>kernel/domainname=foo</literal> are equivalent and | |
61 | will cause <literal>foo</literal> to be written to | |
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62 | <filename>/proc/sys/kernel/domainname</filename>. Either |
63 | <literal>net.ipv4.conf.enp3s0/200.forwarding</literal> or | |
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64 | <literal>net/ipv4/conf/enp3s0.200/forwarding</literal> may be used to refer to |
65 | <filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>. A glob | |
66 | <citerefentry><refentrytitle>glob</refentrytitle><manvolnum>7</manvolnum></citerefentry> pattern may be | |
67 | used to write the same value to all matching keys. Keys for which an explicit pattern exists will be | |
68 | excluded from any glob matching. In addition, a key may be explicitly excluded from being set by any | |
69 | matching glob patterns by specifying the key name prefixed with a <literal>-</literal> character and not | |
70 | followed by <literal>=</literal>, see SYNOPSIS.</para> | |
798d3a52 | 71 | |
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72 | <para>Any access permission errors and attempts to write variables not present on the local system are |
73 | logged, but do not cause the service to fail. Debug log level is used, which means that the message will | |
74 | not show up at all by default. Moreover, if a variable assignment is prefixed with a single | |
75 | <literal>-</literal> character, any failure to set the variable will be logged at debug level, but will | |
76 | not cause the service to fail. All other errors when setting variables are logged with higher priority | |
77 | and cause the service to return failure at the end (other variables are still processed).</para> | |
e08be649 | 78 | |
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79 | <para>The settings configured with <filename>sysctl.d</filename> files will be applied early on boot. The |
80 | network interface-specific options will also be applied individually for each network interface as it | |
81 | shows up in the system. (More specifically, <filename>net.ipv4.conf.*</filename>, | |
82 | <filename>net.ipv6.conf.*</filename>, <filename>net.ipv4.neigh.*</filename> and | |
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83 | <filename>net.ipv6.neigh.*</filename>).</para> |
84 | ||
85 | <para>Many sysctl parameters only become available when certain | |
86 | kernel modules are loaded. Modules are usually loaded on demand, | |
87 | e.g. when certain hardware is plugged in or network brought up. | |
88 | This means that | |
89 | <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> | |
90 | which runs during early boot will not configure such parameters if | |
91 | they become available after it has run. To set such parameters, it | |
92 | is recommended to add an | |
93 | <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
94 | rule to set those parameters when they become available. | |
95 | Alternatively, a slightly simpler and less efficient option is to | |
96 | add the module to | |
97 | <citerefentry><refentrytitle>modules-load.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
98 | causing it to be loaded statically before sysctl settings are | |
99 | applied (see example below).</para> | |
100 | </refsect1> | |
101 | ||
102 | <xi:include href="standard-conf.xml" xpointer="confd" /> | |
103 | ||
104 | <refsect1> | |
105 | <title>Examples</title> | |
106 | <example> | |
107 | <title>Set kernel YP domain name</title> | |
108 | <para><filename>/etc/sysctl.d/domain-name.conf</filename>: | |
109 | </para> | |
110 | ||
111 | <programlisting>kernel.domainname=example.com</programlisting> | |
112 | </example> | |
113 | ||
114 | <example> | |
9407bc2d | 115 | <title>Apply settings available only when a certain module is loaded (method one)</title> |
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116 | <para><filename>/etc/udev/rules.d/99-bridge.rules</filename>: |
117 | </para> | |
118 | ||
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119 | <programlisting>ACTION=="add", SUBSYSTEM=="module", KERNEL=="br_netfilter", \ |
120 | RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge" | |
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121 | </programlisting> |
122 | ||
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123 | <para><filename>/etc/sysctl.d/bridge.conf</filename>: |
124 | </para> | |
71418295 | 125 | |
798d3a52 | 126 | <programlisting>net.bridge.bridge-nf-call-ip6tables = 0 |
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127 | net.bridge.bridge-nf-call-iptables = 0 |
128 | net.bridge.bridge-nf-call-arptables = 0 | |
129 | </programlisting> | |
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130 | |
131 | <para>This method applies settings when the module is | |
b938cb90 | 132 | loaded. Please note that, unless the <filename>br_netfilter</filename> |
9407bc2d | 133 | module is loaded, bridged packets will not be filtered by |
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134 | Netfilter (starting with kernel 3.18), so simply not loading the |
135 | module is sufficient to avoid filtering.</para> | |
798d3a52 | 136 | </example> |
71418295 | 137 | |
798d3a52 | 138 | <example> |
9407bc2d | 139 | <title>Apply settings available only when a certain module is loaded (method two)</title> |
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140 | <para><filename>/etc/modules-load.d/bridge.conf</filename>: |
141 | </para> | |
7284335a | 142 | |
9407bc2d | 143 | <programlisting>br_netfilter</programlisting> |
7284335a | 144 | |
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145 | <para><filename>/etc/sysctl.d/bridge.conf</filename>: |
146 | </para> | |
c91faef3 | 147 | |
798d3a52 | 148 | <programlisting>net.bridge.bridge-nf-call-ip6tables = 0 |
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149 | net.bridge.bridge-nf-call-iptables = 0 |
150 | net.bridge.bridge-nf-call-arptables = 0 | |
151 | </programlisting> | |
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152 | |
153 | <para>This method forces the module to be always loaded. Please | |
b938cb90 | 154 | note that, unless the <filename>br_netfilter</filename> module is |
a8eaaee7 | 155 | loaded, bridged packets will not be filtered with Netfilter |
9407bc2d | 156 | (starting with kernel 3.18), so simply not loading the module is |
a8eaaee7 | 157 | sufficient to avoid filtering.</para> |
798d3a52 | 158 | </example> |
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159 | |
160 | <example> | |
161 | <title>Set network routing properties for all interfaces</title> | |
7b9289b1 | 162 | <para><filename>/etc/sysctl.d/20-rp_filter.conf</filename>:</para> |
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163 | |
164 | <programlisting>net.ipv4.conf.default.rp_filter = 2 | |
165 | net.ipv4.conf.*.rp_filter = 2 | |
166 | -net.ipv4.conf.all.rp_filter | |
167 | net.ipv4.conf.hub0.rp_filter = 1 | |
168 | </programlisting> | |
169 | ||
170 | <para>The <option>rp_filter</option> key will be set to "2" for all interfaces, except "hub0". We set | |
171 | <filename>net.ipv4.conf.default.rp_filter</filename> first, so any interfaces which are added | |
172 | <emphasis>later</emphasis> will get this value (this also covers any interfaces detected while we're | |
173 | running). The glob matches any interfaces which were detected <emphasis>earlier</emphasis>. The glob | |
174 | will also match <filename>net.ipv4.conf.all.rp_filter</filename>, which we don't want to set at all, so | |
175 | it is explicitly excluded. And "hub0" is excluded from the glob because it has an explicit setting. | |
176 | </para> | |
177 | </example> | |
178 | ||
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179 | </refsect1> |
180 | ||
181 | <refsect1> | |
182 | <title>See Also</title> | |
183 | <para> | |
184 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
185 | <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, | |
186 | <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
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187 | <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
188 | <citerefentry project='man-pages'><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
189 | <citerefentry project='man-pages'><refentrytitle>modprobe</refentrytitle><manvolnum>8</manvolnum></citerefentry> | |
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190 | </para> |
191 | </refsect1> | |
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192 | |
193 | </refentry> |