journald: Log error when failed to get machine-id on start

[thirdparty/systemd.git] / man / sysctl.d.xml

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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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  Copyright 2011 Lennart Poettering

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<refentry id="sysctl.d">

        <refentryinfo>
                <title>sysctl.d</title>
                <productname>systemd</productname>

                <authorgroup>
                        <author>
                                <contrib>Developer</contrib>
                                <firstname>Lennart</firstname>
                                <surname>Poettering</surname>
                                <email>lennart@poettering.net</email>
                        </author>
                </authorgroup>
        </refentryinfo>

        <refmeta>
                <refentrytitle>sysctl.d</refentrytitle>
                <manvolnum>5</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sysctl.d</refname>
                <refpurpose>Configure kernel parameters at boot</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <para><filename>/etc/sysctl.d/*.conf</filename></para>
                <para><filename>/run/sysctl.d/*.conf</filename></para>
                <para><filename>/usr/lib/sysctl.d/*.conf</filename></para>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <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>

                <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>Each configuration file shall be named in the
                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 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
                same variable name, the entry in the file with the
                alphabetically 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>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>
        </refsect1>

        <refsect1>
                <title>Example</title>
                <example>
                        <title>/etc/sysctl.d/domain-name.conf example:</title>

                        <programlisting># Set kernel YP domain name
kernel.domainname=example.com</programlisting>
                </example>
        </refsect1>

        <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>
                </para>
        </refsect1>

</refentry>