source: networking/netprogs/ntp.xml@ dd9e0c3

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
  <!ENTITY % general-entities SYSTEM "../../general.ent">
  %general-entities;

  <!ENTITY ntp-download-http "https://www.eecis.udel.edu/~ntp/ntp_spool/ntp4/ntp-4.2/ntp-&ntp-version;.tar.gz">
<!--  <!ENTITY ntp-download-ftp  "&gentoo-ftp-repo;/ntp-&ntp-version;.tar.gz">-->
  <!ENTITY ntp-download-ftp  " ">
  <!ENTITY ntp-md5sum        "46dfba933c3e4bc924d8e55068797578">
  <!ENTITY ntp-size          "6.8 MB">
  <!ENTITY ntp-buildsize     "94 MB (with tests)">
  <!ENTITY ntp-time          "0.8 SBU (with tests)">
]>

<sect1 id="ntp" xreflabel="ntp-&ntp-version;">
  <?dbhtml filename="ntp.html"?>

  <sect1info>
    <othername>$LastChangedBy$</othername>
    <date>$Date$</date>
  </sect1info>

  <title>ntp-&ntp-version;</title>

  <indexterm zone="ntp">
    <primary sortas="a-ntp">ntp</primary>
  </indexterm>

  <sect2 role="package">
    <title>Introduction to ntp</title>

    <para>The <application>ntp</application> package contains a
    client and server to keep the time synchronized between various computers over
    a network. This package is the official reference implementation of the
    NTP protocol.</para>

    &lfs79_checked;

    <bridgehead renderas="sect3">Package Information</bridgehead>
    <itemizedlist spacing="compact">
      <listitem>
        <para>Download (HTTP): <ulink url="&ntp-download-http;"/></para>
      </listitem>
      <listitem>
        <para>Download (FTP): <ulink url="&ntp-download-ftp;"/></para>
      </listitem>
      <listitem>
        <para>Download MD5 sum: &ntp-md5sum;</para>
      </listitem>
      <listitem>
        <para>Download size: &ntp-size;</para>
      </listitem>
      <listitem>
        <para>Estimated disk space required: &ntp-buildsize;</para>
      </listitem>
      <listitem>
        <para>Estimated build time: &ntp-time;</para>
      </listitem>
    </itemizedlist>

    <bridgehead renderas="sect3">ntp Dependencies</bridgehead>

    <bridgehead renderas="sect4">Required</bridgehead>
    <para role="required">
      <xref linkend="wget"/> (runtime, for <command>update-leap</command>) and
      <xref linkend="which"/>
    </para>

    <bridgehead renderas="sect4">Optional</bridgehead>
    <para role="optional">
      <xref linkend="libcap-pam"/>,
      <xref linkend="libevent"/>,
      <xref linkend="openssl"/>,
      <ulink url="http://www.thrysoee.dk/editline/">libedit</ulink>, and
      <ulink url="https://www.gnu.org/software/autogen/">libopts from
      AutoGen</ulink>
    </para>

    <para condition="html" role="usernotes">User Notes:
    <ulink url="&blfs-wiki;/ntp"/></para>

  </sect2>

  <sect2 role="installation">
    <title>Installation of ntp</title>

    <para>
      There should be a dedicated user and group to take control
      of the <command>ntpd</command> daemon after it is
      started. Issue the following commands as the
      <systemitem class="username">root</systemitem> user:
    </para>

<screen role="root"><userinput>groupadd -g 87 ntp &amp;&amp;
useradd -c "Network Time Protocol" -d /var/lib/ntp -u 87 \
        -g ntp -s /bin/false ntp</userinput></screen>

    <para>Install <application>ntp</application> by running
    the following commands:</para>

<screen><userinput>./configure --prefix=/usr         \
            --bindir=/usr/sbin    \
            --sysconfdir=/etc     \
            --enable-linuxcaps    \
            --with-lineeditlibs=readline \
            --docdir=/usr/share/doc/ntp-&ntp-version; &amp;&amp;
make</userinput></screen>

    <para>To test the results, issue: <command>make check</command>.</para>

    <para>Now, as the <systemitem class="username">root</systemitem> user:</para>

<screen role="root"><userinput>make install &amp;&amp;
install -v -o ntp -g ntp -d /var/lib/ntp</userinput></screen>

  </sect2>

  <sect2 role="commands">
    <title>Command Explanations</title>

    <para><parameter>--bindir=/usr/sbin</parameter>: This parameter places
    the administrative programs in <filename
    class="directory">/usr/sbin</filename>.</para>

    <para><parameter>--enable-linuxcaps</parameter>: ntpd is run as user
    ntp, so use Linux capabilities for non-root clock control.</para>

    <para><option>--with-lineeditlibs=readline</option>: This option enables
    <application>Readline</application> support for <command>ntpdc</command>
    and <command>ntpq</command> programs. If omitted,
    <application>libedit</application> will be used if installed, otherwise no
    readline capabilites will be compiled.</para>

  </sect2>

  <sect2 role="configuration">
    <title>Configuring ntp</title>

    <sect3 id="ntp-config">
      <title>Config Files</title>

      <para><filename>/etc/ntp.conf</filename></para>

      <indexterm zone="ntp ntp-config">
        <primary sortas="e-etc-ntp.conf">/etc/ntp.conf</primary>
      </indexterm>

    </sect3>

    <sect3>
      <title>Configuration Information</title>

      <para>The following configuration file first defines various ntp
      servers with open access from different continents. Second, it
      creates a drift file where <command>ntpd</command> stores the
      frequency offset and a pid file to store the
      <command>ntpd</command> process ID. Third, it defines the location
      for the leap-second definition file
      <filename>/etc/ntp.leapseconds</filename>, that the
      <command>update-leap</command> script checks and updates, when
      necessary. This script can be run as a cron job and the
      <application>ntp</application> developers recommend a frequency of
      about three weeks for the updates. Since the documentation included
      with the package is sparse, visit the ntp website at
      <ulink url="http://www.ntp.org/"/> and
      <ulink url="http://www.pool.ntp.org/"/> for more information.</para>

<screen role="root"><userinput>cat &gt; /etc/ntp.conf &lt;&lt; "EOF"
<literal># Asia
server 0.asia.pool.ntp.org

# Australia
server 0.oceania.pool.ntp.org

# Europe
server 0.europe.pool.ntp.org

# North America
server 0.north-america.pool.ntp.org

# South America
server 2.south-america.pool.ntp.org

driftfile /var/lib/ntp/ntp.drift
pidfile   /var/run/ntpd.pid

leapfile  /etc/ntp.leapseconds</literal>
EOF</userinput></screen>

      <para>
        You may wish to add a <quote>Security session</quote>. For
        explanations, see
        <ulink url="https://www.eecis.udel.edu/~mills/ntp/html/accopt.html#restrict"/>.
      </para>

<screen role="root"><userinput>cat &gt;&gt; /etc/ntp.conf &lt;&lt; "EOF"
<literal># Security session
restrict    default limited kod nomodify notrap nopeer noquery
restrict -6 default limited kod nomodify notrap nopeer noquery

restrict 127.0.0.1
restrict ::1</literal>
EOF</userinput></screen>

    </sect3>

    <sect3  id="ntp-init">
      <title>Synchronizing the Time</title>

      <para>There are two options. Option one is to run <command>ntpd</command>
      continuously and allow it to synchronize the time in a gradual manner. The
      other option is to run <command>ntpd</command> periodically (using cron)
      and update the time each time <command>ntpd</command> is scheduled.</para>

      <para>
        To start the <command>ntpd</command> daemon at boot,
        install the systemd unit from the <xref linkend="bootscripts"/>
        package by running the following command as the
        <systemitem class="username">root</systemitem> user:
      </para>

      <indexterm zone="ntp ntp-init">
        <primary sortas="f-ntp">ntp</primary>
      </indexterm>

<screen role="root"><userinput>make install-ntpd</userinput></screen>

      <para>If you prefer to run <command>ntpd</command> periodically, add the
      following command to <systemitem class="username">root</systemitem>'s
      <filename>crontab</filename>:</para>

<screen><literal>ntpd -q</literal></screen>

    </sect3>

  </sect2>

  <sect2 role="content">
    <title>Contents</title>

    <segmentedlist>
      <segtitle>Installed Programs</segtitle>
      <segtitle>Installed Libraries</segtitle>
      <segtitle>Installed Directories</segtitle>

      <seglistitem>
        <seg>calc_tickadj, ntp-keygen, ntp-wait, ntpd, ntpdate, ntpdc, ntpq,
        ntptime, ntptrace, sntp, tickadj and update-leap</seg>
        <seg>None</seg>
        <seg>/usr/share/ntp,
        /usr/share/doc/ntp-4.2.8 and
        /var/lib/ntp</seg>
      </seglistitem>
    </segmentedlist>

    <variablelist>
      <bridgehead renderas="sect3">Short Descriptions</bridgehead>
      <?dbfo list-presentation="list"?>
      <?dbhtml list-presentation="table"?>

      <varlistentry id="calc_tickadj">
        <term><command>calc_tickadj</command></term>
        <listitem>
          <para>calculates optimal value for tick given ntp drift file.</para>
          <indexterm zone="ntp calc_tickadj">
            <primary sortas="b-calc_tickadj">calc_tickadj</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ntp-keygen">
        <term><command>ntp-keygen</command></term>
        <listitem>
          <para>generates cryptographic data files used by the NTPv4 authentication
          and identification schemes.</para>
          <indexterm zone="ntp ntp-keygen">
            <primary sortas="b-ntp-keygen">ntp-keygen</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ntp-wait">
        <term><command>ntp-wait</command></term>
        <listitem>
          <para>is useful at boot time, to delay the boot sequence until
          <command>ntpd</command> has set the time.</para>
          <indexterm zone="ntp ntp-wait">
            <primary sortas="b-ntp-wait">ntp-wait</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ntpd">
        <term><command>ntpd</command></term>
        <listitem>
          <para>is a ntp daemon that runs in the background and keeps
          the date and time synchronized based on response from configured
          ntp servers. It also functions as a ntp server.</para>
          <indexterm zone="ntp ntpd">
            <primary sortas="b-ntpd">ntpd</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ntpdate">
        <term><command>ntpdate</command></term>
        <listitem>
          <para>is a client program that sets the date and time based on
          the response from an ntp server. This command is deprecated.</para>
          <indexterm zone="ntp ntpdate">
            <primary sortas="b-ntpdate">ntpdate</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ntpdc">
        <term><command>ntpdc</command></term>
        <listitem>
          <para>is used to query the ntp daemon about its current state
          and to request changes in that state.</para>
          <indexterm zone="ntp ntpdc">
            <primary sortas="b-ntpdc">ntpdc</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ntpq">
        <term><command>ntpq</command></term>
        <listitem>
          <para>is a utility program used to monitor <command>ntpd</command>
          operations and determine performance.</para>
          <indexterm zone="ntp ntpq">
            <primary sortas="b-ntpq">ntpq</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ntptime">
        <term><command>ntptime</command></term>
        <listitem>
          <para>reads and displays time-related kernel variables.</para>
          <indexterm zone="ntp ntptime">
            <primary sortas="b-ntptime">ntptime</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="ntptrace">
        <term><command>ntptrace</command></term>
        <listitem>
          <para>traces a chain of ntp servers back to the primary source.</para>
          <indexterm zone="ntp ntptrace">
            <primary sortas="b-ntptrace">ntptrace</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="sntp">
        <term><command>sntp</command></term>
        <listitem>
          <para>is a Simple Network Time Protocol (SNTP) client.</para>
          <indexterm zone="ntp sntp">
            <primary sortas="b-sntp">sntp</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="tickadj">
        <term><command>tickadj</command></term>
        <listitem>
          <para>reads, and optionally modifies, several timekeeping-related
          variables in older kernels that do not have support for precision
          timekeeping.</para>
          <indexterm zone="ntp tickadj">
            <primary sortas="b-tickadj">tickadj</primary>
          </indexterm>
        </listitem>
      </varlistentry>

      <varlistentry id="update-leap">
        <term><command>update-leap</command></term>
        <listitem>
          <para>is a script to verify and, if necessary, update the leap-second
          definition file.</para>
          <indexterm zone="ntp update-leap">
            <primary sortas="b-update-leap">update-leap</primary>
          </indexterm>
        </listitem>
      </varlistentry>

    </variablelist>

  </sect2>

</sect1>