Date: Fri, 31 Jan 2014 21:54:18 +0000 (UTC) From: Dru Lavigne <dru@FreeBSD.org> To: doc-committers@freebsd.org, svn-doc-all@freebsd.org, svn-doc-head@freebsd.org Subject: svn commit: r43711 - head/en_US.ISO8859-1/books/handbook/network-servers Message-ID: <201401312154.s0VLsI7D021560@svn.freebsd.org>
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Author: dru Date: Fri Jan 31 21:54:18 2014 New Revision: 43711 URL: http://svnweb.freebsd.org/changeset/doc/43711 Log: White space fix only. Translators can ignore. Sponsored by: iXsystems Modified: head/en_US.ISO8859-1/books/handbook/network-servers/chapter.xml Modified: head/en_US.ISO8859-1/books/handbook/network-servers/chapter.xml ============================================================================== --- head/en_US.ISO8859-1/books/handbook/network-servers/chapter.xml Fri Jan 31 21:35:11 2014 (r43710) +++ head/en_US.ISO8859-1/books/handbook/network-servers/chapter.xml Fri Jan 31 21:54:18 2014 (r43711) @@ -5228,39 +5228,38 @@ Starting smbd.</screen> <title>Clock Synchronization with NTP</title> <indexterm><primary>NTP</primary> - <secondary>ntpd</secondary> + <secondary>ntpd</secondary> </indexterm> - <para>Over time, a computer's clock is prone to drift. This is - problematic as many network services require the computers on a network - to share the same accurate time. Accurate time is also needed to ensure - that file timestamps stay - consistent. The - Network Time Protocol (<acronym>NTP</acronym>) is one way to provide clock - accuracy in a network.</para> - - <para>&os; includes &man.ntpd.8; - which can be configured to query other - <acronym>NTP</acronym> servers in order to - synchronize the clock on that machine or to provide time services to - other computers in the network. The servers which are queried - can be local to the network or provided by an <acronym>ISP</acronym>. - In addition, an <link - xlink:href="http://support.ntp.org/bin/view/Servers/WebHome">online - list of publicly accessible <acronym>NTP</acronym> servers</link> - is available. When choosing a public <acronym>NTP</acronym> server, select - one that is geographically close and - review its usage policy.</para> - - <para>Choosing several <acronym>NTP</acronym> servers is recommended in - case one of the servers becomes unreachable or - its clock proves unreliable. As <application>ntpd</application> receives responses, - it favors - reliable servers over the less reliable ones.</para> - - <para>This section describes how to configure <application>ntpd</application> on &os;. Further documentation can be found in - <filename>/usr/share/doc/ntp/</filename> in HTML - format.</para> + <para>Over time, a computer's clock is prone to drift. This is + problematic as many network services require the computers on a + network to share the same accurate time. Accurate time is also + needed to ensure that file timestamps stay consistent. The + Network Time Protocol (<acronym>NTP</acronym>) is one way to + provide clock accuracy in a network.</para> + + <para>&os; includes &man.ntpd.8; which can be configured to query + other <acronym>NTP</acronym> servers in order to synchronize the + clock on that machine or to provide time services to other + computers in the network. The servers which are queried can be + local to the network or provided by an <acronym>ISP</acronym>. + In addition, an <link + xlink:href="http://support.ntp.org/bin/view/Servers/WebHome">online + list of publicly accessible <acronym>NTP</acronym> + servers</link> is available. When choosing a public + <acronym>NTP</acronym> server, select one that is geographically + close and review its usage policy.</para> + + <para>Choosing several <acronym>NTP</acronym> servers is + recommended in case one of the servers becomes unreachable or + its clock proves unreliable. As <application>ntpd</application> + receives responses, it favors reliable servers over the less + reliable ones.</para> + + <para>This section describes how to configure + <application>ntpd</application> on &os;. Further documentation + can be found in <filename>/usr/share/doc/ntp/</filename> in HTML + format.</para> <sect2> <title><acronym>NTP</acronym> Configuration</title> @@ -5270,115 +5269,117 @@ Starting smbd.</screen> <tertiary>ntpdate</tertiary> </indexterm> - <para>To only synchronize the clock when a system boots, - use &man.ntpdate.8;. This alone can be appropriate for - desktops which are frequently rebooted. However, - most systems should - run <application>ntpdate</application> at boot time as well as configure <application>ntpd</application>. - This is because <application>ntpd</application> - changes the clock gradually, whereas <application>ntpdate</application> - sets the clock, no matter how great the difference between a - machine's current clock setting and the correct time.</para> - - <para>To enable <application>ntpdate</application> at boot time, add - <literal>ntpdate_enable="YES"</literal> to - <filename>/etc/rc.conf</filename>. To also enable - <application>ntpd</application>, add the <literal>ntpd_enable="YES"</literal> - entry to <filename>/etc/rc.conf</filename>. Additional variables can be specified - in <filename>/etc/rc.conf</filename>. Refer to &man.rc.conf.5;, - &man.ntpdate.8;, and &man.ntpd.8; for details.</para> - - <para>Both applications - read <filename>/etc/ntp.conf</filename> to determine - which servers to query. Here is a simple example of an - <filename>/etc/ntp.conf</filename>:</para> + <para>To only synchronize the clock when a system boots, use + &man.ntpdate.8;. This alone can be appropriate for desktops + which are frequently rebooted. However, most systems should + run <application>ntpdate</application> at boot time as well as + configure <application>ntpd</application>. This is because + <application>ntpd</application> changes the clock gradually, + whereas <application>ntpdate</application> sets the clock, no + matter how great the difference between a machine's current + clock setting and the correct time.</para> + + <para>To enable <application>ntpdate</application> at boot time, + add <literal>ntpdate_enable="YES"</literal> to + <filename>/etc/rc.conf</filename>. To also enable + <application>ntpd</application>, add the + <literal>ntpd_enable="YES"</literal> entry to + <filename>/etc/rc.conf</filename>. Additional variables can + be specified in <filename>/etc/rc.conf</filename>. Refer to + &man.rc.conf.5;, &man.ntpdate.8;, and &man.ntpd.8; for + details.</para> + + <para>Both applications read <filename>/etc/ntp.conf</filename> + to determine which servers to query. Here is a simple example + of an <filename>/etc/ntp.conf</filename>:</para> - <example> - <title> Sample <filename>/etc/ntp.conf</filename></title> + <example> + <title> Sample <filename>/etc/ntp.conf</filename></title> <programlisting>server ntplocal.example.com prefer server timeserver.example.org server ntp2a.example.net driftfile /var/db/ntp.drift</programlisting> - </example> + </example> - <para>The format of this file is - described in &man.ntp.conf.5;. The <literal>server</literal> option specifies which - servers to query, with one server listed on each line. - If a server entry includes <literal>prefer</literal>, - that server is preferred over other servers. A response - from a preferred server will be discarded if it differs - significantly from responses; otherwise it - will be used. - The <literal>prefer</literal> argument should only be used for - <acronym>NTP</acronym> servers that are known to be highly accurate, such as - those with special time monitoring hardware.</para> - - <para>The <literal>driftfile</literal> entry specifies which - file is used to store the system clock's frequency offset. - <application>ntpd</application> uses this to automatically - compensate for the clock's natural drift, allowing it to - maintain a reasonably correct setting even if it is cut off - from all external time sources for a period of time. This - file also stores information about previous responses - from <acronym>NTP</acronym> servers. Since this file contains - internal information for <acronym>NTP</acronym>, it should not be modified.</para> - - <para>By default, an <acronym>NTP</acronym> server is accessible to any - network host. The <literal>restrict</literal> - option in <filename>/etc/ntp.conf</filename> can be used to - control which systems can access the server. For example, - to deny all machines from accessing the <acronym>NTP</acronym> - server, add the following line to - <filename>/etc/ntp.conf</filename>:</para> + <para>The format of this file is described in &man.ntp.conf.5;. + The <literal>server</literal> option specifies which servers + to query, with one server listed on each line. If a server + entry includes <literal>prefer</literal>, that server is + preferred over other servers. A response from a preferred + server will be discarded if it differs significantly from + responses; otherwise it will be used. The + <literal>prefer</literal> argument should only be used for + <acronym>NTP</acronym> servers that are known to be highly + accurate, such as those with special time monitoring + hardware.</para> + + <para>The <literal>driftfile</literal> entry specifies which + file is used to store the system clock's frequency offset. + <application>ntpd</application> uses this to automatically + compensate for the clock's natural drift, allowing it to + maintain a reasonably correct setting even if it is cut off + from all external time sources for a period of time. This + file also stores information about previous responses + from <acronym>NTP</acronym> servers. Since this file contains + internal information for <acronym>NTP</acronym>, it should not + be modified.</para> + + <para>By default, an <acronym>NTP</acronym> server is accessible + to any network host. The <literal>restrict</literal> option + in <filename>/etc/ntp.conf</filename> can be used to control + which systems can access the server. For example, to deny all + machines from accessing the <acronym>NTP</acronym> server, add + the following line to + <filename>/etc/ntp.conf</filename>:</para> - <programlisting>restrict default ignore</programlisting> + <programlisting>restrict default ignore</programlisting> <note> - <para>This will also prevent access from other <acronym>NTP</acronym> servers. - If there is a - need to synchronize with an external <acronym>NTP</acronym> + <para>This will also prevent access from other + <acronym>NTP</acronym> servers. If there is a need to + synchronize with an external <acronym>NTP</acronym> server, allow only that specific server. Refer to &man.ntp.conf.5; for more information.</para> </note> - <para>To allow machines within the network to synchronize - their clocks with the server, but ensure they are not - allowed to configure the server or be used as peers to - synchronize against, instead use:</para> - - <programlisting>restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap</programlisting> - - <para>where - <systemitem class="ipaddress">192.168.1.0</systemitem> is the - local network address and - <systemitem class="netmask">255.255.255.0</systemitem> is - the network's subnet mask.</para> - - <para>Multiple <literal>restrict</literal> entries are supported. - For more - details, refer to the <literal>Access Control Support</literal> - subsection of &man.ntp.conf.5;.</para> - - <para>Once - <literal>ntpd_enable="YES"</literal> has been added to - <filename>/etc/rc.conf</filename>, <application>ntpd</application> - can be started now without rebooting the system by typing:</para> + <para>To allow machines within the network to synchronize their + clocks with the server, but ensure they are not allowed to + configure the server or be used as peers to synchronize + against, instead use:</para> + + <programlisting>restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap</programlisting> + + <para>where <systemitem + class="ipaddress">192.168.1.0</systemitem> is the local + network address and <systemitem + class="netmask">255.255.255.0</systemitem> is the network's + subnet mask.</para> + + <para>Multiple <literal>restrict</literal> entries are + supported. For more details, refer to the <literal>Access + Control Support</literal> subsection of + &man.ntp.conf.5;.</para> + + <para>Once <literal>ntpd_enable="YES"</literal> has been added + to <filename>/etc/rc.conf</filename>, + <application>ntpd</application> can be started now without + rebooting the system by typing:</para> <screen>&prompt.root; <userinput>service ntpd start</userinput></screen> </sect2> <sect2> - <title>Using <acronym>NTP</acronym> with a <acronym>PPP</acronym> - Connection</title> + <title>Using <acronym>NTP</acronym> with a + <acronym>PPP</acronym> Connection</title> <para><application>ntpd</application> does not need a permanent connection to the Internet to function properly. However, if a <acronym>PPP</acronym> connection is configured to dial out - on demand, <acronym>NTP</acronym> traffic should be prevented from - triggering a dial out or keeping the connection alive. This can be configured - with <literal>filter</literal> + on demand, <acronym>NTP</acronym> traffic should be prevented + from triggering a dial out or keeping the connection alive. + This can be configured with <literal>filter</literal> directives in <filename>/etc/ppp/ppp.conf</filename>. For example:</para> @@ -5398,8 +5399,8 @@ driftfile /var/db/ntp.drift</programlist <note> <para>Some Internet access providers block low-numbered ports, - preventing NTP from functioning since replies never - reach the machine.</para> + preventing NTP from functioning since replies never reach + the machine.</para> </note> </sect2> </sect1>
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