X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=man%2Fsysctl.d.xml;h=3002ebd0fdc13bcbca3206793e0e7fac2ea4a5c9;hp=155427cecf03d09b5a61ab97fe5bb3888e1926d5;hb=1b600437bac3c0676cc72f589909c4cbfe38ba10;hpb=7b4977254cdc1203b44211e00cdb3a0c318cfcf2

diff --git a/man/sysctl.d.xml b/man/sysctl.d.xml
index 155427cec..3002ebd0f 100644
--- a/man/sysctl.d.xml
+++ b/man/sysctl.d.xml
@@ -68,13 +68,8 @@
                 <para>The configuration files contain a list of
                 variable assignments, separated by newlines. Empty
                 lines and lines whose first non-whitespace character
-                is # or ; are ignored.</para>
-
-                <para>Note that both / and . are accepted as label
-                separators within sysctl variable
-                names. <literal>kernel.domainname=foo</literal> and
-                <literal>kernel/domainname=foo</literal> hence are
-                entirely equivalent.</para>
+                is <literal>#</literal> or <literal>;</literal> are
+                ignored.</para>
 
                 <para>Each configuration file shall be named in the
                 style of <filename><replaceable>program</replaceable>.conf</filename>.
@@ -89,29 +84,106 @@
                 administrator, who may use this logic to override the
                 configuration files installed by vendor packages. All
                 configuration files are sorted by their filename in
-                alphabetical order, regardless in which of the
-                directories they reside. If multiple files specify the
+                lexicographic order, regardless of which of the
+                directories they reside in. If multiple files specify the
                 same variable name, the entry in the file with the
-                alphabetically latest name will be applied. It is
+                lexicographically latest name will be applied. It is
                 recommended to prefix all filenames with a two-digit
                 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
                 <filename>/dev/null</filename> in
                 <filename>/etc/sysctl.d/</filename> bearing the
                 same filename.</para>
+
+                <para>The settings configured with
+                <filename>sysctl.d</filename> files will be applied
+                early on boot. The network interface-specific options
+                will also be applied individually for each network
+                interface as it shows up in the system. (More
+                specifically,
+                <filename>net.ipv4.conf.*</filename>,
+                <filename>net.ipv6.conf.*</filename>,
+                <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 bridged packets (method one)</title>
+                        <para><filename>/etc/udev/rules.d/99-bridge.rules</filename>:
+                        </para>
+
+                        <programlisting>ACTION=="add", SUBSYSTEM=="module", KERNEL=="bridge", RUN+="/usr/lib/systemd/systemd-sysctl --prefix=/net/bridge"
+</programlisting>
+
+                        <para><filename>/etc/sysctl.d/bridge.conf</filename>:
+                        </para>
+
+                        <programlisting>net.bridge.bridge-nf-call-ip6tables = 0
+net.bridge.bridge-nf-call-iptables = 0
+net.bridge.bridge-nf-call-arptables = 0
+</programlisting>
+                </example>
+
+                <example>
+                        <title>Disable packet filter on bridged packets (method two)</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>
 
@@ -123,6 +195,7 @@ 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>