[system-administrators-guide] Add: Configure ntpdate Servers

[stephenw]

commit f6d4f8067811a27b494333f5182b9dcc1a80a028
Author: Stephen Wadeley <swadeley at redhat.com>
Date:   Thu Jul 31 09:53:51 2014 +0200

    Add: Configure ntpdate Servers

 en-US/Configuring_NTP_Using_ntpd.xml |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)
---
diff --git a/en-US/Configuring_NTP_Using_ntpd.xml b/en-US/Configuring_NTP_Using_ntpd.xml
index 8b36ccd..e14ebdc 100644
--- a/en-US/Configuring_NTP_Using_ntpd.xml
+++ b/en-US/Configuring_NTP_Using_ntpd.xml
@@ -392,6 +392,30 @@ synchronised to NTP server (10.5.26.10) at stratum 2
 
   </section>
 
+<section id="s1-Configure_ntpdate_Servers">
+  <title>Configure ntpdate Servers</title>
+  <para>
+    The purpose of the <systemitem class="daemon">ntpdate</systemitem> service is to set the clock during system boot. This was used previously to ensure that the services started after <systemitem class="daemon">ntpdate</systemitem> would have the correct time and not observe a jump in the clock. The use of <systemitem class="daemon">ntpdate</systemitem> and the list of step-tickers is considered deprecated and so Fedora uses the <option>-g</option> option to the <command>ntpd</command> command and not <systemitem class="daemon">ntpdate</systemitem> by default.
+  </para>
+  <para>
+    The <systemitem class="daemon">ntpdate</systemitem> service in Fedora is mostly useful only when used alone without <systemitem class="daemon">ntpd</systemitem>. With <application>systemd</application>, which starts services in parallel, enabling the <systemitem class="daemon">ntpdate</systemitem> service will not ensure that other services started after it will have correct time unless they specify an ordering dependency on <literal>time-sync.target</literal>, which is provided by the <systemitem class="daemon">ntpdate</systemitem> service. The <systemitem class="service">ntp-wait</systemitem> service (in the <package>ntp-perl</package> subpackage) provides the <literal>time-sync</literal> target for the <systemitem class="daemon">ntpd</systemitem> service. In order to ensure a service starts with correct time, add <literal>After=time-sync.target</literal> to the service and enable one of the services which provide the target (<systemitem class="daemon">ntpdate</systemi
 tem> or <application>sntp</application>, or <application>ntp-wait</application> if <systemitem class="daemon">ntpd</systemitem> is enabled). Some services on Fedora have the dependency included by default ( for example, <systemitem class="daemon">dhcpd</systemitem>, <systemitem class="daemon">dhcpd6</systemitem>, and <systemitem class="daemon">crond</systemitem>).
+  </para>
+ <para>
+  To check if the <systemitem class="daemon">ntpdate</systemitem> service is enabled to run at system start, issue the following command:
+  <screen>~]$ <command>systemctl status ntpdate</command></screen>
+</para>
+<para>
+ To enable the service to run at system start, issue the following command as <systemitem class="username">root</systemitem>:
+  <screen>~]# <command>systemctl enable ntpdate</command></screen>
+</para>
+
+<para>
+  In Fedora the default <filename>/etc/ntp/step-tickers</filename> file contains <literal>0.fedora.pool.ntp.org</literal>. To configure additional <systemitem class="daemon">ntpdate</systemitem> servers, using a text editor running as <systemitem class="username">root</systemitem>, edit <filename>/etc/ntp/step-tickers</filename>. The number of servers listed is not very important as <systemitem class="daemon">ntpdate</systemitem> will only use this to obtain the date information once when the system is starting. If you have an internal time server then use that host name for the first line. An additional host on the second line as a backup is sensible. The selection of backup servers and whether the second host is internal or external depends on your risk assessment. For example, what is the chance of any problem affecting the first server also affecting the second server? Would connectivity to an external server be more likely to be available than connectivity to internal s
 ervers in the event of a network failure disrupting access to the first server?
+</para>
+
+</section>
+
+
 <section id="s1-Configure_NTP">
   <title>Configure NTP</title>
   <para>