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
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
|
<!--startcut ======================================================= -->
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html><head>
<META NAME="generator" CONTENT="lgazmail v1.1preB">
<TITLE>The Answer Guy 32:
The BIOS Clock, Y2K, Linux and Everything
</TITLE>
<!-- ORIGINAL SUBJECT:
linux, y2k and the system BIOS clock
JTD SUBTITLE:
-->
</head>
<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#A000A0"
ALINK="#FF0000">
<H4>"Linux Gazette...<I>making Linux just a little more fun!</I>"
</H4>
<P> <hr> <P>
<!-- ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: -->
<H1 align="center"><A NAME="answer">
<img src="../gx/dennis/qbubble.gif" alt="" border="0" align="middle">
<a href="./lg_toc32.html">The Answer Guy</a>
<img src="../gx/dennis/bbubble.gif" alt="" border="0" align="middle">
</A></H1>
<BR>
<H4 align="center">By James T. Dennis,
<a href="mailto:answerguy@ssc.com">answerguy@ssc.com</a>
<BR>Starshine Technical Services, <A HREF="http://www.starshine.org/">http://www.starshine.org/</A>
</H4>
<p><hr><p>
<!--endcut ========================================================= -->
<H3><img src="../gx/dennis/qbub.gif" alt="(?)"
width="50" height="28" align="left" border="0"
>The BIOS Clock, Y2K, Linux and Everything</H3>
<p><strong>From Ward, David on 12 Aug 1998 </strong></p>
<!-- begin body -->
<strong><p>How does linux keep track of "real time". Does it get its
information from the BIOS system clock, or can it keep track of time
by setting the correct time zone, and setting the time, even though
the BIOS is incorrectly reporting the "real time"?.
</p></strong>
<strong><p>Thanks,
<br>David Ward
</p></strong>
<blockquote><img src="../gx/dennis/bbub.gif" height="28" width="50"
alt="(!)" border="0"
>Linux's initial clock settings (at boot up) are from
the BIOS. However, the kernel internally keeps its
own time thereafter.
</blockquote>
<blockquote>It turns out that there is an immense about of work that
is done on system clock synchronization over the Internet
and among Unix systems.
</blockquote>
<blockquote>I'm assuming that you're concerned about some specific
systems that have a buggy BIOS --- that you know will
report invalid dates after the year 2000.
</blockquote>
<blockquote>To detect this condition you could use a script like:
</blockquote>
<blockquote><blockquote><code>CURRENT_YEAR=$( date +%Y )
<br>FILE_YEAR=$( find /etc/README -printf "%TY" )
<p>
<br>[ $CURRENT_YEAR -eq $FILE_YEAR ] || {
<br># We've suffered a backslip: the current 4 digit
<br># year arimetically precedes the date on our
<br># marker file
<br>logger "Backslip in Time Detected ... Fixing"
<br># Recover here....
<br># After recovery and during shutdown, when
<br># the clock is in a known good state, we can
<br># touch the marker file to unsure that it's
<br># date is periodically updated.
<br>}
</code></blockquote></blockquote>
<blockquote>... note that I'm using the <tt>$()</tt> (Korn/bash) construct
rather than the equivalent "backtick" operators. This is
to avoid ambiguity; the effect is the same.
</blockquote>
<blockquote>One way to ensure that you have the correct date set on
your system is to use the '<tt>ntpdate</tt>' command around boot
time. This sets your clock based on that of another
system. Oddly enough, though this command is included on
many Linux systems, there often seems to be no man page
installed for it. However I've read the man pages at
(<A HREF="http://www.eecis.udel.edu/~ntp"
>http://www.eecis.udel.edu/~ntp</A>) --- and they don't
make things any easier.
</blockquote>
<blockquote>With all due respect to Mr. Mills (one of the key figures
in the NTP system) these pages (man and web) look like they
were written for a federal funding grant. A simple HOWTO
would be nice. (Maybe I'm just stupid but these pages seem
to talk about everything <EM>other than</EM> how does a typical
home or SOHO sysadmin configure their systems to have the
correct time).
</blockquote>
<blockquote>In any event here's the command I use to initially set
my date:
</blockquote>
<blockquote><blockquote><code
>/usr/sbin/ntpdate -s ntp.ucsd.edu ns.scruz.net ntp1.cs.wisc.edu
</code></blockquote></blockquote>
<blockquote>... this calls the ntpdate command and lists three time
servers (stratum-2 in this case). In the complicated world
of NTP the "stratum" of a clock is a measure of how "far" it
is from the NIST atomic clocks which are used as the international
standards. In essense it is a measure of the time server's
"authority" (as in 'how authoritative is that answer'). It
isn't actually a measure of how "accurate" that clock is, just
how many hops are between it and the top of the hierarchy.
</blockquote>
<blockquote>Thus my system (betelgeuse) becomes a "stratum-3" NTP server
after I refer to these "stratum-2" servers. It is the system
that I use to set the time for the rest of the house. After
the time is initially set I periodically re-run this command
to reset it. It reports to me the adjustment that it makes
(typically under one second).
</blockquote>
<blockquote>This is <EM>NOT</EM> recommended practice.
(Mixing <tt>ntpdate</tt> and <tt>xntpd</tt>
on a system). However, in my case, I don't want to configure
my <tt>xntpd</tt> to refer to those same servers since it would mean
that my ISDN router would fire up an unnecessary connection to
the Internet every twenty minutes round the clock. Since I
have no easy way to prevent this (the ISDN router I'm using is
a separate box) I choose do use my method.
</blockquote>
<blockquote>If you have a full time connection to the Internet then the
best solution is to use the <tt>xntpd</tt> (extended Network Time
Protocol Daemon) to keep your system clocks in sync with a set
of time servers. I'd set up one or two systems on your
'perimeter' network (the one that's exposed to the Internet
--- assuming you have a firewall). Then I'd have the rest
of your systems use that (or those) as their time reference.
</blockquote>
<blockquote><tt>xntpd</tt> also includes support for a couple of dozen GPS and
radio clock devices. These range from a couple hundred
to a few thousand dollars (and typically connect to your
host via a serial line).
</blockquote>
<blockquote>In all cases <tt>ntpdate</tt> and <tt>xntpd</tt> use
sophisticated protocols to measure latency and network communications delays and
to account for deviations between the reference servers.
You're pretty well guaranteed sub-second accuracy when you use them.
</blockquote>
<blockquote>In some versions and configurations, the NTP suite supports
cryptographic integrity preservation methods, to prevent
spurious and hostiles changes to your network time references.
</blockquote>
<blockquote>The web pages I referred to above does have a wealth of
details about the protocols and the suite. If you can manage
to decode it into a set of simple instructions for us
"tape apes" I'd love to see it written up as a HOW-TO.
Perhaps the subscribers to the
<a href="news://comp.protocols.time.ntp">comp.protocols.time.ntp</a>
newsgroup might be more helpful.
</blockquote>
<blockquote>(My e-mail exchange with Mr. Mills on this issue was not
terribly helpful).
</blockquote>
<blockquote>There is one existing mini-HOWTO that could be expanded
to suit the bill:
</blockquote>
<blockquote>
<dl><dt>Clock Mini-HOWTO:
<dd><A HREF="http://www.ssc.com/linux/LDP/HOWTO/mini/Clock.html"
>http://www.ssc.com/linux/LDP/HOWTO/mini/Clock.html</A>
(written by Roy Bean).
</dl>
</blockquote>
<blockquote>... it only contains a few words about <tt>xntpd</tt>.
</blockquote>
<blockquote>Also, someone once told me about a GPS reciever that was
very inexpensive. It had no display, only a DB-9 serial
connector. If anyone out there knows of a reliable source
for these, I'd like to know about it, and I'll be happy to
publish the URL. I wouldn't mind paying $100 for a good
time source --- but two or three hundred is just too much
for my applications.
</blockquote>
<!-- end body -->
<!--startcut ======================================================= -->
<P> <hr> <P>
<H5 align="center"><a href="http://www.linuxgazette.com/ssc.copying.html"
>Copyright ©</a> 1998, James T. Dennis <BR>
Published in <I>Linux Gazette</I> Issue 32 September 1998</H5>
<P> <hr> <P>
<!--::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::-->
<table width="98%"><tr valign="center" align="center">
<td rowspan="3"><A HREF="../lg_answer32.html"><IMG
SRC="../gx/dennis/answernew.gif"
ALT="[ Answer Guy Index ]"></A></td>
<td><A HREF="tag_phreak.html">phreak</A>
<td><A HREF="tag_abandon.html">abandon</A>
<td><A HREF="tag_javaterm.html">javaterm</A>
<td><A HREF="tag_BBS.html">BBS</A>
<td><A HREF="tag_flaws.html">flaws</A>
<td><A HREF="tag_doslinux.html">doslinux</A>
<td><A HREF="tag_resume.html">resume</A>
</tr><tr valign="center" align="center">
<td><A HREF="tag_softwindows.html">softwindows</A>
<td><A HREF="tag_convert.html">convert</A>
<td><A HREF="tag_apache.html">apache</A>
<td><A HREF="tag_emulate.html">emulate</A>
<td><A HREF="tag_database.html">database</A>
<td><A HREF="tag_distrib.html">distrib</A>
<td><A HREF="tag_proxy.html">proxy</A>
</tr><tr valign="center" align="center">
<td><A HREF="tag_disable.html">disable</A>
<td><A HREF="tag_DVI.html">DVI</A>
<td><A HREF="tag_superblock.html">superblock</A>
<td><A HREF="tag_serial.html">serial</A>
<td><A HREF="tag_permission.html">permission</A>
<td><A HREF="tag_detach.html">detach</A>
<td><A HREF="tag_cdr.html">cdr</A>
</tr><tr valign="center" align="center">
<td><A HREF="tag_rs422.html">rs422</A>
<td><A HREF="tag_modem.html">modem</A>
<td><A HREF="tag_notfound.html">notfound</A>
<td><A HREF="tag_tuning.html">tuning</A>
<td><A HREF="tag_libc5.html">libc5</A>
<td><A HREF="tag_startup.html">startup</A>
<td><A HREF="tag_clock.html">clock</A>
<td><A HREF="tag_ping.html">ping</A>
</tr><tr valign="center" align="center">
<td><A HREF="tag_accounts.html">accounts</A>
<td><A HREF="tag_lilo.html">lilo</A>
<td><A HREF="tag_NDS.html">NDS</A>
<td><A HREF="tag_95slow.html">95slow</A>
<td><A HREF="tag_nonlinux.html">nonlinux</A>
<td><A HREF="tag_progenv.html">progenv</A>
<td><A HREF="tag_cluster.html">cluster</A>
<td><A HREF="tag_ftpd.html">ftpd</A>
</tr></table>
<P> <hr> <P>
<!--::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::-->
<A HREF="./lg_toc32.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_bytes32.html"><IMG SRC="../gx/back2.gif"
ALT="[ Previous Section ]"></A>
<A HREF="./stemen.html"><IMG SRC="../gx/fwd.gif"
ALT="[ Next Section ]"></A>
<!--::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::-->
</body>
</html>
<!--endcut ========================================================= -->
|
