1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
|
<!--startcut ======================================================= -->
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html>
<head>
<META NAME="generator" CONTENT="lgazmail v1.1I.e">
<TITLE>The Answer Guy 38: How 'ntpdate' finds IP addresses?</TITLE>
</HEAD><BODY BGCOLOR="#FFFFFF" TEXT="#000000"
LINK="#3366FF" VLINK="#A000A0">
<!-- ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: -->
<H4>"The Linux Gazette...<I>making Linux just a little more fun!</I>"</H4>
<P> <hr> <P>
<!-- ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: -->
<center>
<H1><A NAME="answer">
<img src="../../gx/dennis/qbubble.gif" alt="(?)"
border="0" align="middle">
<font color="#B03060">The Answer Guy</font>
<img src="../../gx/dennis/bbubble.gif" alt="(!)"
border="0" align="middle">
</A></H1>
<BR>
<H4>By James T. Dennis,
<a href="mailto:linux-questions-only@ssc.com">linux-questions-only@ssc.com</a><BR>
Starshine Technical Services,
<A HREF="http://www.starshine.org/">http://www.starshine.org/</A>
</H4>
</center>
<p><hr><p>
<!-- endcut ======================================================= -->
<!-- begin 28 -->
<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
height="50" width="60" alt="(?) " border="0"
>How 'ntpdate' finds IP addresses?</H3>
<p><strong>From Pete O'Donnell on Tue, 23 Feb 1999
</strong></p>
<!-- ::
How 'ntpdate' finds IP addresses?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:: -->
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
In an article on setting system clocks to atomic clock time, you referred to
the following line:
</STRONG></P>
<PRE><STRONG><code>
/usr/sbin/ntpdate -s ntp.ucsd.edu ns.scruz.net ntp1.cs.wisc.edu
</code></STRONG></PRE>
<P><STRONG>
Do these 3 servers have entries in the <TT>/etc/ntp.conf</TT> file or
is there some sort of host file set up on your machine? How does the
<tt>xntpd</tt> daemon find the corresponding IPs. Let me know.
Thanks answer guy.
</STRONG></P>
<P><STRONG>
-Pete O'Donnell
<br>LiveNetworking
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
The <TT>/etc/ntp.conf</TT> file is used by xntpd --- not be
by the ntpdate command. The '<tt>ntpdate</tt>' command finds
IP addresses that correspond to these host names in
the same way that any other Unix utility or application
does. Almost all Unix utilities that do any sort of
network operation are linked against a set of "resolver"
libraries. The "resolver" libraries differ a bit
among systems --- but most of them look in the <TT>/etc/hosts</TT>
file, for a hostname match (grabbing an IP address from
there if they find one) and then read the <TT>/etc/resolv.conf</TT>
file for a list of nameservers (DNS). In other cases
your resolver libraries might make requests (RPCs?) of
one or more NIS (YP) servers in your NIS domain, and
newer configurations --- using glibc's modular NSS (name
services switching) as controlled by <TT>/etc/nsswitch.conf</TT>
might query LDAP, NDS (Novell) or other backend
directory/name services systems for their mapping.
</BLOCKQUOTE>
<BLOCKQUOTE>
(Under libc5 there was a <TT>/etc/hosts.conf</TT> that gave more
limited and less extensible control over which name services
were/are queried and in which order).
</BLOCKQUOTE>
<BLOCKQUOTE>
Read the man pages for those files (<TT>/etc/hosts</TT>,
<TT>/etc/nsswitch.conf</TT>, <TT>/etc/hosts.conf</TT> and
<TT>/etc/resolv.conf</TT>) for some details. You can also look at
<A HREF="http://www.openldap.org"
>http://www.openldap.org</A> for some cool info about future
use/deployment of LDAP.
</BLOCKQUOTE>
<!-- sig -->
<!-- end 28 -->
<!--startcut ======================================================= -->
<P> <hr> <P>
<H5 align="center"><a href="http://www.linuxgazette.com/copying.html"
>Copyright ©</a> 1999, James T. Dennis
<BR>Published in <I>The Linux Gazette</I> Issue 38 March 1999</H5>
<P> <hr> <P>
<!-- begin tagnav ::::::::::::::::::::::::::::::::::::::::::::::::::-->
<TABLE WIDTH="96%"><TR VALIGN="center" ALIGN="center">
<TD ROWSPAN="3" COLSPAN="4" WIDTH="24%"><A HREF="../lg_answer38.html"
><IMG SRC="../../gx/dennis/answernew.gif"
ALT="[ Answer Guy Index ]"></A></td>
<TD WIDTH="6%"><A HREF="1.html">1</A></TD>
<TD WIDTH="6%"><A HREF="2.html">2</A></TD>
<TD WIDTH="6%"><A HREF="3.html">3</A></TD>
<TD WIDTH="6%"><A HREF="4.html">4</A></TD>
<TD WIDTH="6%"><A HREF="5.html">5</A></TD>
<TD WIDTH="6%"><A HREF="6.html">6</A></TD>
<TD WIDTH="6%"><A HREF="7.html">7</A></TD>
<TD WIDTH="6%"><A HREF="8.html">8</A></TD>
<TD WIDTH="6%"><A HREF="9.html">9</A></TD>
<TD WIDTH="6%"><A HREF="10.html">10</A></TD>
<TD WIDTH="6%"><A HREF="11.html">11</A></TD>
</TR><TR VALIGN="center" ALIGN="center">
<TD><A HREF="12.html">12</A></TD>
<TD> </TD>
<TD><A HREF="14.html">14</A></TD>
<TD> </TD>
<TD><A HREF="16.html">16</A></TD>
<TD><A HREF="17.html">17</A></TD>
<TD><A HREF="18.html">18</A></TD>
<TD><A HREF="19.html">19</A></TD>
<TD> </TD>
<TD><A HREF="21.html">21</A></TD>
<TD><A HREF="22.html">22</A></TD>
</TR><TR VALIGN="center" ALIGN="center">
<TD><A HREF="23.html">23</A></TD>
<TD><A HREF="24.html">24</A></TD>
<TD> </TD>
<TD><A HREF="26.html">26</A></TD>
<TD> </TD>
<TD><A HREF="28.html">28</A></TD>
<TD><A HREF="29.html">29</A></TD>
<TD><A HREF="30.html">30</A></TD>
<TD><A HREF="31.html">31</A></TD>
<TD><A HREF="32.html">32</A></TD>
<TD> </TD>
</TR></TABLE>
<!-- end tagnav ::::::::::::::::::::::::::::::::::::::::::::::::::::-->
<P> <hr> <P>
<!-- begin lgnav ::::::::::::::::::::::::::::::::::::::::::::::::::: -->
<A HREF="../index.html"
><IMG SRC="../../gx/indexnew.gif" ALT="[ Table Of Contents ]"></A>
<A HREF="../../index.html"
><IMG SRC="../../gx/homenew.gif" ALT="[ Front Page ]"></A>
<A HREF="../lg_bytes38.html"
><IMG SRC="../../gx/back2.gif" ALT="[ Previous Section ]"></A>
<A HREF="../lg_tips38.html"
><IMG SRC="../../gx/fwd.gif" ALT="[ Next Section ]"></A>
<!-- end lgnav ::::::::::::::::::::::::::::::::::::::::::::::::::::: -->
<!-- ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: -->
</BODY></HTML>
<!--endcut ========================================================= -->
|
