lfs-book/chapter07/systemd-custom.xml

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<sect1 id="ch-scripts-systemd-custom">
  <?dbhtml filename="systemd-custom.html"?>

  <title>Systemd Usage and Configuration</title>

  <indexterm zone="ch-scripts-systemd-custom">
    <primary sortas="e-Systemd">Systemd Customization</primary>
  </indexterm>

  <sect2>
    <title>Basic Configuration</title>

    <para>The <filename>/etc/systemd/system.conf</filename> file contains a set
    of options to control basic systemd operations. The default file has all
    entries commented out with the default settings indicated. This file is
    where the log level may be changed as well as some basic logging settings.
    See <filename>systemd-system.conf(5)</filename> manual page for details on
    each configuration option.</para>

  </sect2>

  <sect2>
    <title>Disabling Screen Clearing at Boot Time</title>

    <para>The normal behavior for systemd is to clear the secreen at
    the end of the boot sequence. If desired, this behavior may be
    changed by running the following command:</para>

<screen role="nodump"><userinput>mkdir -pv /etc/systemd/system/getty@tty1.service.d

cat &gt; /etc/systemd/system/getty@tty1.service.d/noclear.conf &lt;&lt; EOF
<literal>[Service]
TTYVTDisallocate=no</literal>
EOF</userinput></screen>

    <para>The boot messages can always be revied by using the
    <userinput>journalctl -b</userinput> command as the root user.</para>

  </sect2>

  <sect2>
    <title>Disabling tmpfs for /tmp</title>

    <para>By default, <filename class="directory">/tmp</filename> is created as
    a tmpfs. If this is not desired, it can be overridden by the following:</para>

<screen role="nodump"><userinput>ln -sfv /dev/null /etc/systemd/system/tmp.mount</userinput></screen>

    <para>This is not necessary if there is a separate partition for
    <filename class="directory">/tmp</filename> specified in
    <filename>/etc/fstab</filename>.</para>

  </sect2>

  <sect2>
    <title>Configuring Automatic File Creation and Deletion</title>

    <para>There are several services that create or delete files or
    directories:</para>

    <itemizedlist>
      <listitem><para>systemd-tmpfiles-clean.service</para></listitem>
      <listitem><para>systemd-tmpfiles-setup-dev.service</para></listitem>
      <listitem><para>systemd-tmpfiles-setup.service</para></listitem>
    </itemizedlist>
  
    <para>The system location for the configuration files is
    <filename>/usr/lib/tmpfiles.d/*.conf</filename>. The local 
    configuration files are in
    <filename class="directory">/etc/tmpfiles.d</filename>. Files in
    <filename class="directory">/etc/tmpfiles.d</filename> override
    files with the same name in
    <filename class="directory">/usr/lib/tmpfiles.d</filename>. See
    <filename>tmpfiles.d(5)</filename> manual page  for file format
    details.</para>

  </sect2>

  <sect2>
    <title>Overriding Default Services Behavior</title>

    <para>A systemd service contents can be overriden by creating a directory
    and a configuration file in <filename
    class="directory">/etc/systemd/system</filename>. For example:</para>

<screen role="nodump"><userinput>mkdir -pv /etc/systemd/system/foobar.service.d

cat > /etc/systemd/system/foobar.service.d/foobar.conf &lt;&lt; EOF
<literal>[Service]
Restart=always
RestartSec=30</literal>
EOF</userinput></screen>

     <para>See <filename>systemd.unit(5)</filename> manual page for more
     information. After creating the configuration file, run
     <userinput>systemctl daemon-reload</userinput> and <userinput>systemctl
     restart foobar</userinput> to activate the changes to a service.</para>

  </sect2>

  <sect2>
    <title>Debugging the Boot Sequence</title>

    <para>There are several commands that can be used to help debug the systemd 
    boot process. Here are some examples:</para>

    <itemizedlist>
       <listitem><para>systemctl list-units -t service [--all]</para></listitem>
       <listitem><para>systemctl list-units -t target  [--all]</para></listitem>
       <listitem><para>systemctl show -p Wants multi-user.target</para></listitem>
       <listitem><para>systemctl status sshd.service</para></listitem>
    </itemizedlist>

  </sect2>

</sect1>