From 59fccb9cb4eba406dbee93864638cc52f6ee7d4a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Thu, 19 Jun 2014 20:43:56 -0400
Subject: [PATCH] man: document statically loading modules for sysctl settings
https://bugzilla.redhat.com/show_bug.cgi?id=1022977
https://bugzilla.novell.com/show_bug.cgi?id=725412
(cherry picked from commit 7284335adbb8cb2bc9c11f9e102906da1bf71145)
---
man/sysctl.d.xml | 79 +++++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 56 insertions(+), 23 deletions(-)
diff --git a/man/sysctl.d.xml b/man/sysctl.d.xml
index db53b495..78c4e80b 100644
--- a/man/sysctl.d.xml
+++ b/man/sysctl.d.xml
@@ -71,24 +71,6 @@
is <literal>#</literal> or <literal>;</literal> are
ignored.</para>
- <para>Note that either <literal>/</literal> or
- <literal>.</literal> may be used as separators within
- sysctl variable names. If the first separator is a
- slash, remaining slashes and dots are left intact. If
- the first separator is a dot, dots and slashes are
- interchanged. <literal>kernel.domainname=foo</literal>
- and <literal>kernel/domainname=foo</literal> are
- equivalent and will cause <literal>foo</literal> to
- be written to
- <filename>/proc/sys/kernel/domainname</filename>.
- Either
- <literal>net.ipv4.conf.enp3s0/200.forwarding</literal>
- or
- <literal>net/ipv4/conf/enp3s0.200/forwarding</literal>
- may be used to refer to
- <filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>.
- </para>
-
<para>Each configuration file shall be named in the
style of <filename><replaceable>program</replaceable>.conf</filename>.
Files in <filename>/etc/</filename> override files
@@ -110,6 +92,24 @@
number and a dash, to simplify the ordering of the
files.</para>
+ <para>Note that either <literal>/</literal> or
+ <literal>.</literal> may be used as separators within
+ sysctl variable names. If the first separator is a
+ slash, remaining slashes and dots are left intact. If
+ the first separator is a dot, dots and slashes are
+ interchanged. <literal>kernel.domainname=foo</literal>
+ and <literal>kernel/domainname=foo</literal> are
+ equivalent and will cause <literal>foo</literal> to
+ be written to
+ <filename>/proc/sys/kernel/domainname</filename>.
+ Either
+ <literal>net.ipv4.conf.enp3s0/200.forwarding</literal>
+ or
+ <literal>net/ipv4/conf/enp3s0.200/forwarding</literal>
+ may be used to refer to
+ <filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>.
+ </para>
+
<para>If the administrator wants to disable a
configuration file supplied by the vendor, the
recommended way is to place a symlink to
@@ -125,16 +125,48 @@
specifically,
<filename>net.ipv4.conf.*</filename>,
<filename>net.ipv6.conf.*</filename>,
- <filename>net.ipv4.neigh.*</filename> and <filename>net.ipv6.neigh.*</filename>)</para>
+ <filename>net.ipv4.neigh.*</filename> and <filename>net.ipv6.neigh.*</filename>).</para>
+
+ <para>Many sysctl parameters only become available
+ when certain kernel modules are loaded. Modules are
+ usually loaded on demand, e.g. when certain hardware
+ is plugged in or network brought up. This means that
+ <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> which runs
+ during early boot will not configure such parameters
+ if they become available after it has run. To
+ set such parameters, it is recommended to add
+ an <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> rule to set those parameters when they become
+ available. Alternatively, a slightly simpler and
+ less efficient option is to add the module to
+ <citerefentry><refentrytitle>modules-load.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>, causing it to be loaded statically
+ before sysctl settings are applied (see
+ example below).</para>
</refsect1>
<refsect1>
- <title>Example</title>
+ <title>Examples</title>
+ <example>
+ <title>Set kernel YP domain name</title>
+ <para><filename>/etc/sysctl.d/domain-name.conf</filename>:
+ </para>
+
+ <programlisting>kernel.domainname=example.com</programlisting>
+ </example>
+
<example>
- <title>/etc/sysctl.d/domain-name.conf example:</title>
+ <title>Disable packet filter on the bridge</title>
+ <para><filename>/etc/modules-load.d/bridge.conf</filename>:
+ </para>
+
+ <programlisting>bridge</programlisting>
+
+ <para><filename>/etc/sysctl.d/bridge.conf</filename>:
+ </para>
- <programlisting># Set kernel YP domain name
-kernel.domainname=example.com</programlisting>
+ <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
+net.bridge.bridge-nf-call-iptables = 0
+net.bridge.bridge-nf-call-arptables = 0
+</programlisting>
</example>
</refsect1>
@@ -146,6 +178,7 @@ kernel.domainname=example.com</programlisting>
<citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sysctl.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ <citerefentry><refentrytitle>modprobe</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>