commit 1a70a965f32fb4f9d946fb53ba22a3bb8629add2
Author: Stephen Wadeley <swadeley(a)redhat.com>
Date: Mon Oct 14 22:41:02 2013 +0200
Adding: chapter id="ch-Configuring_NTP_using_ntpd"
Chapter link was incorrect
en-US/Configuring_NTP_using_ntpd.xml | 20 ++++++++------------
1 files changed, 8 insertions(+), 12 deletions(-)
---
diff --git a/en-US/Configuring_NTP_using_ntpd.xml b/en-US/Configuring_NTP_using_ntpd.xml
index 4e3c993..10b3ca8 100644
--- a/en-US/Configuring_NTP_using_ntpd.xml
+++ b/en-US/Configuring_NTP_using_ntpd.xml
@@ -42,7 +42,7 @@
<para>
Atomic Clocks and their signals broadcast over Radio and GPS
</para>
- <itemizedlist>
+ <itemizedlist>
<listitem>
<para>
GPS (Global Positioning System)
@@ -104,7 +104,7 @@
</listitem>
</varlistentry>
-<varlistentry>
+ <varlistentry>
<term>Stratum 15:</term>
<listitem>
<para>
@@ -112,8 +112,6 @@
</para>
</listitem>
</varlistentry>
-
-
</variablelist>
@@ -136,7 +134,7 @@
<para>
The <systemitem class="protocol">NTP</systemitem> protocol
provides additional information to improve accuracy. Four timestamps are used to allow the
calculation of round-trip time and server response time. In order for a system in its role
as <systemitem class="protocol">NTP</systemitem> client to
synchronize with a reference time server, a packet is sent with an <quote>originate
timestamp</quote>. When the packet arrives, the time server adds a
<quote>receive timestamp</quote>. After processing the request for time and
date information and just before returning the packet, it adds a <quote>transmit
timestamp</quote>. When the returning packet arrives at the <systemitem
class="protocol">NTP</systemitem> client, a <quote>receive
timestamp</quote> is generated. The client can now calculate the total round trip
time and by subtracting the processing time derive the actual traveling time. By assuming
the outgoing and return trips take equal time, the single-trip delay in re
ceiving the <systemitem class="protocol">NTP</systemitem> data is
calculated. The full <systemitem class="protocol">NTP</systemitem>
algorithm is much more complex then presented here.</para>
<para>
- Each packet containing time information received is not immediately acted upon, but
is subject to validation checks and then used together with several other samples to
arrive at a reasonably good estimate of the time. This is then compared to the system
clock to determine the time offset, that is to say, the difference between the system
clock's time and what <systemitem
class="service">ntpd</systemitem> has determined the time should be.
The system clock is adjusted slowly, at most at a rate of 0.5ms per second, to reduce this
offset by changing the frequency of the counter being used. It will take at least 2000
seconds to adjust the clock by 1 second using this method. This slow change is referred to
as slewing and cannot go backwards. If the time offset of the clock is more than 128ms
(the default setting), <systemitem class="service">ntpd</systemitem>
can <quote>step</quote> the clock forwards or backwards. If the time offset at
system start is greater than 1000 sec
onds then the user, or an installation script, should make a manual adjustment. See
<xref linkend="ch-Date_and_Time_Configuration" />. With the
<option>-g</option> option to the <command>ntpd</command> command
(used by default), any offset at system start will be corrected, but during normal
operation only offsets of up to 1000 seconds will be corrected.</para>
+ Each packet containing time information received is not immediately acted upon, but
is subject to validation checks and then used together with several other samples to
arrive at a reasonably good estimate of the time. This is then compared to the system
clock to determine the time offset, that is to say, the difference between the system
clock's time and what <systemitem
class="service">ntpd</systemitem> has determined the time should be.
The system clock is adjusted slowly, at most at a rate of 0.5ms per second, to reduce this
offset by changing the frequency of the counter being used. It will take at least 2000
seconds to adjust the clock by 1 second using this method. This slow change is referred to
as slewing and cannot go backwards. If the time offset of the clock is more than 128ms
(the default setting), <systemitem class="service">ntpd</systemitem>
can <quote>step</quote> the clock forwards or backwards. If the time offset at
system start is greater than 1000 sec
onds then the user, or an installation script, should make a manual adjustment. See
<xref linkend="ch-Configuring_the_Date_and_Time" />. With the
<option>-g</option> option to the <command>ntpd</command> command
(used by default), any offset at system start will be corrected, but during normal
operation only offsets of up to 1000 seconds will be corrected.</para>
<para>
Some software may fail or produce an error if the time is changed backwards. For
systems that are sensitive to step changes in the time, the threshold can be changed to
600s instead of 128ms using the <option>-x</option> option (unrelated to the
<option>-g</option> option). Using the <option>-x</option> option
to increase the stepping limit from 0.128s to 600s has a drawback because a different
method of controlling the clock has to be used. It disables the kernel clock discipline
and may have a negative impact on the clock accuracy. The <option>-x</option>
option can be added to the <filename>/etc/sysconfig/ntpd</filename>
configuration file.</para>
</section>
@@ -354,17 +352,16 @@ synchronised to NTP server (10.5.26.10) at stratum 2
</para>
<para>
- Check if the firewall is configured to allow incoming <systemitem
class="protocol">NTP</systemitem> traffic for clients using the
graphical <application>Firewall Configuaration</application> tool.
+ Check if the firewall is configured to allow incoming <systemitem
class="protocol">NTP</systemitem> traffic for clients using the
graphical <application>Firewall Configuration</application>
tool.</para>
<!-- need to check this new part -->
<para>
- To start the graphical <application>firewall-config</application>
tool, press the super key and start typing <command>firewall</command>. The
<guiicon>firewall</guiicon> icon will appear. Press enter once it is
highlighted. The <application>firewall-config</application> tool appears. You
will be prompted for your user password. <remark>CHECKME Tested on Fedora 19
</remark></para>
- <para>
+ To start the graphical <application>firewall-config</application>
tool, press the super key and start typing <command>firewall</command>. The
<guiicon>firewall</guiicon> icon will appear. Press enter once it is
highlighted. The <application>firewall-config</application> tool appears. You
will be prompted for your user password.</para>
<para>
To start the graphical firewall configuration tool using the command line, enter
the following command as root user:
<screen>~]# <command>firewall-config</command></screen>
- The <guilabel>Firewall Configuration</guilabel> window opens. Note,
this command can be run as normal user but you will then be prompted for the root password
from time to time.<remark>CHECKME: Need to check if its user or root password on
Fedora 19</remark>
+ The <guilabel>Firewall Configuration</guilabel> window opens. Note,
this command can be run as normal user but you will then be prompted for the root password
from time to time.
</para>
<para>
Look for the word <quote>Connected</quote> in the lower left corner.
This indicates that the <application>firewall-config</application> tool is
connected to the user space daemon, <systemitem
class="daemon">firewalld</systemitem>.
@@ -395,7 +392,7 @@ synchronised to NTP server (10.5.26.10) at stratum 2
</para>
</section>
-</section>
+ </section>
<section id="s1-Configure_ntpdate_servers">
<title>Configure ntpdate Servers</title>
@@ -770,8 +767,7 @@ In the above example, the kernel is using
<application>kvm-clock</application>.
<para>
To override the default clock source, add a line similar to the following in
<filename>grub.conf</filename>:
<screen>clocksource=tsc</screen>
- The available clock source is architecture dependent. <!-- See the Kernel
Parameters documentation
<filename>/usr/share/doc/kernel-doc-*/Documentation/kernel-parameters.txt</filename>.
Note that this documentation is not installed by default. I think normal users do not need
to know this. See s2-ntpd-docs-optional-inst -->
- </para>
+ The available clock source is architecture dependent.</para>
</section>