<refsect1>
<title>Description</title>
- <para><command>systemd</command> uses configuration
- files from the above directories to configure
- <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
- kernel parameters during boot.</para>
+ <para>At boot,
+ <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ reads configuration files from the above directories
+ to configure
+ <citerefentry><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ kernel parameters.</para>
</refsect1>
<refsect1>
- <title>Configuration Format</title>
+ <title>Configuration Format</title>
- <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>
+ <para>The configuration files contain a list of
+ variable assignments, separated by newlines. Empty
+ lines and lines whose first non-whitespace character
+ is <literal>#</literal> or <literal>;</literal> are
+ ignored.</para>
<para>Each configuration file shall be named in the
- style of <filename><program>.conf</filename>.
- Files in <filename>/run/</filename> override files
- with the same name in <filename>/usr/lib/</filename>.
- Files in <filename>/etc</filename> override files with
- the same name in <filename>/run/</filename> and
- <filename>/usr/lib/</filename>. Packages should
- install their configuration files in
+ style of <filename><replaceable>program</replaceable>.conf</filename>.
+ Files in <filename>/etc/</filename> override files
+ with the same name in <filename>/usr/lib/</filename>
+ and <filename>/run/</filename>. Files in
+ <filename>/run/</filename> override files with the same
+ name in <filename>/usr/lib/</filename>. Packages
+ should install their configuration files in
<filename>/usr/lib/</filename>. Files in
<filename>/etc/</filename> are reserved for the local
administrator, who may use this logic to override the
- configuration installed by vendor packages. All
- configuration files are sorted by their name in
- alphabetical order, regardless in which of the
- directories they reside, to guarantee that a specific
- configuration file takes precedence over another file
- with an alphabetically earlier name, if both files
- contain the same variable setting.</para>
+ configuration files installed by vendor packages. All
+ configuration files are sorted by their filename in
+ 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
+ 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
+ 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> carrying with the
- same name.</para>
+ <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>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=/proc/sys/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>/etc/sysctl.d/domain-name.conf example:</title>
+ <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>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-sysctl.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <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>
~ianmdlvl / elogind.git / blobdiff