362 lines
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362 lines
15 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<HTML>
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<HEAD>
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<TITLE></TITLE>
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<META NAME="GENERATOR" CONTENT="StarOffice/5.0 (Unix)">
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<META NAME="AUTHOR" CONTENT="Ron Jenkins">
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<META NAME="CREATED" CONTENT="19990327;17313200">
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<META NAME="CHANGEDBY" CONTENT="Ron Jenkins">
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<META NAME="CHANGED" CONTENT="19990330;21493100">
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ALINK="#FF0000">
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<!--endcut ============================================================-->
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<H4>
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"Linux Gazette...<I>making Linux just a little more fun!</I>"
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</H4>
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<P> <HR> <P>
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<!--===================================================================-->
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<P ALIGN=CENTER STYLE="margin-bottom: 0.00cm"><FONT SIZE=4><B>Linux
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Primer Series Part 8</B></FONT></P>
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<P ALIGN=CENTER STYLE="margin-bottom: 0.00cm"><FONT SIZE=4><B>Advanced
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Network Services version 03.30.1999</B></FONT></P>
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<P STYLE="margin-bottom: 0.00cm; font-weight: medium"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm; font-weight: medium"><FONT SIZE=3>Copyright
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©1998, 1999 Ron Jenkins. All rights reserved.</FONT></P>
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<P STYLE="margin-bottom: 0.00cm; font-weight: medium"><FONT SIZE=3>I
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welcome your suggestions, corrections, criticisms, and comments. I
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may be reached at the following address - <A HREF="mailto:rjenkins62@netscape.net">rjenkins62@netscape.net</A>
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.</FONT></P>
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<P STYLE="margin-bottom: 0.00cm; font-weight: medium"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm; font-weight: medium"><FONT SIZE=3>This
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work is provided on an "as is" basis. The author provides
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no warranty whatsoever, either express or implied, regarding the
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work, including warranties with respect to its merchantability or
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fitness for any particular purpose.</FONT></P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">You may have noticed that my e mail
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address has changed again. My ISP has decided to move to metered
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access, just as my last one did. This seems to be a growing trend,
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at least here in the Midwest.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">To eliminate the need for constantly
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changing this stuff, I have acquired an account @ Netscape, which
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will remain constant, regardless of ISP changes.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">As soon as I can afford it, or can
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find a place to house my webpages, I will post it here.
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Unfortunately, I will be unable to have the updates and enhancements
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to my column on-line until then.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Before I get a flood of "Get a
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Geocities page" messages, let me just say that I have
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requirements that Geocities is unwilling to supply.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">The qni.com address will still be
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functional for a couple of months, to make the transition as smooth
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as possible.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Operating Systems
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Covered/Supported: </B>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Slackware version 3.6 </B>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>RedHat version 5.1 </B>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Windows NT Server version 4.0 </B>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Windows NT Workstation version
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4.0 </B>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>I only test my columns on the
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operating systems specified. I don't have access to a MAC, I don't
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use Windows 95, and have no plans to use Windows 98.</B></P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>If someone would care to provide
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equivalent instructions for any of the above operating systems, I
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will be happy to include them in my documents. </B>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Advanced Network Services:</B></P>
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<P STYLE="margin-bottom: 0.00cm">This month, we will be examining
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some advanced services that you may or may not want to use on your
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home network.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">In particular, we will be looking at
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some options for streamlining the connection scripts, executing
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demand dialing, and time synchronization issues.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">In this month's column, we will be
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looking at the following areas of interest:</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Customization options for the
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connect scripts</P>
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<P STYLE="margin-bottom: 0.00cm">Time Synchronization</P>
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<P STYLE="margin-bottom: 0.00cm">Demand Dialing</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">As always, I will include ant
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distribution specific information as necessary. Unless indicated
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otherwise, the information will apply equally to both distributions.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Customization options for the
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connect scripts:</B></P>
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<P STYLE="margin-bottom: 0.00cm">I can't stress enough the importance
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of assuring that your PPP software is version 2.3 or above. It is
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the added functionality that this software contains that make the
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following things possible.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">With version 2.3 or greater, here
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are some of the things we can do right from the script, rather than
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having to run ancillary programs to accomplish similar functions.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Auto-reconnect - This option is
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enabled using the keyword "persist" in the connect script.
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This eliminates the need for the pppupd software we have been using.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Demand Dialing - This option is
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enabled using the keyword "demand" in the connect script.
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This eliminates the need for a third party program, such as diald.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Therefore, a new revised script
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taking advantage of these options would look something like this:</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Begin connect script example -</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">#!/bin/sh</P>
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<P STYLE="margin-bottom: 0.00cm">pppd connect \</P>
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<P STYLE="margin-bottom: 0.00cm">'chat -v -f /path/to/chat/script'
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/dev/cua1 115200 -detach crtscts modem \</P>
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<P STYLE="margin-bottom: 0.00cm">-proxyarp defaultroute demand
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persist &</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">End connect script example -</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Note that no changes are required to
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your chat script, as this just handles the initial terminal login,
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then hands off to the PPP daemon.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Also, if your ISP's interpretation
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of the phrase "Unlimited Usage" is like mine, you will be
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limited to 10 to 12 hours per day. I would strongly suggest that if
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this is the case, then consider moving to another ISP.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">If you choose to stay, the demand
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dialing function will be required, unless you want to connect
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manually each time, or if you have a regular period of time during
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which you use the Internet, you may want to write a cron job to take
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care of connecting and disconnecting.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">For instance, say you connect from
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8:00 a.m. To 8:00 p.m. every day, and wish to automate the procedure.
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You would simply open your crontab file with the command "crontab
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-e" and enter the following two lines:</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">0 8 * *
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* /path/to/your/connect/script</P>
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<P STYLE="margin-bottom: 0.00cm">0 20 * *
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* /path/to/your/ppp-off/script</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">or staying with our examples we have
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been using:</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">0 8 * * * /sbin/unicom</P>
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<P STYLE="margin-bottom: 0.00cm">0 20 * * * /usr/sbin/ppp-off</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Time Synchronization:</B></P>
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<P STYLE="margin-bottom: 0.00cm">Although we don't often think about
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it, time is very important to the proper operation of computers and
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programs.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Y2K issues aside, many services on
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your network or individual systems depend on an accurate measurement
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of time.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">UNIX and Linux in particular are
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very picky about time discrepancies, and tend to do nasty things to
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your processes and data if two machines disagree about the time.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Briefly, there are two methods of
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acquiring an accurate measurement of time:</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">From an internal device (such as
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your CMOS clock,) or from an external source, such as a time server
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or frequency standard.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">This will be old hat to those of you
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who come from an amateur radio background, but the government has
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just such a source available, and several different options for
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availing yourself of its use.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Your internal CMOS clock is
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unreliable, and dependent upon a constant power source. So in this
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area we will concentrate on synchronizing our machines, and our
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network to an external source.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">The "absolute standard"
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for time is an atomic clock housed at the National Institutes of
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Standards and Technology (NIST) in Fort Collins, Colorado.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">There are many ways to use this
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standard to synchronize your network, ranging from Radio Frequency
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receivers to modem dial up connections, to Global Positioning
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Satellites (GPS.)</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Here we will concentrate on using
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the Internet to accomplish this synchronization.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">The de facto standard for this
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purpose is something called the Network Time Protocol, or NTP. Some
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systems, particularly RedHat based systems, often come with ntp or
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xntp pre-installed. Check the documentation and man pages for more
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information.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">If you are using a Slackware based
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machine, you will have a utility called netdate that will serve the
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same function. You can initiate netdate manually, trough a script,
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or from a cron job. Check the man page for more details.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Either system will require you to
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specify one or more time servers from which accurate data can be
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obtained.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Time Servers are machines that
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collect and dispense accurate time data. They are organized in to
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"stratums" with the lower numbers being the more accurate.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Stratum one servers are usually
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servers that have some sort of direct logical connection to the
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atomic clock, either by radio satellite or modem, and an accurate
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external device to make this connection.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Stratum two servers acquire data
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from the stratum one machines, and pass it along to other stratum two
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machines, or peers, and down to stratum three machines, and so on.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">For most home applications, and
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business applications that do not require a "real time clock,"
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stratum two servers are more than adequate for your needs.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">For a list of time servers, as well
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as the ntp software, see the resources section.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Demand Dialing:</B></P>
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<P STYLE="margin-bottom: 0.00cm">If you have followed the above
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instructions, then this should be a moot point. If you cannot or
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will not upgrade your PPP software to 2.3 or above, you will need to
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use diald or something similar to initiate the demand dialing
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function.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">Configuration of diald or one of the
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other programs is beyond the scope of this document. Check your
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preferred program documentation and man pages for more information.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm">If enough people express interest, I
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will devote a column specifically to this subject in the future.</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Next month, we will conquer Print
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Services. See 'ya then!</B></P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>References:</B></P>
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<P STYLE="margin-bottom: 0.00cm">PPP HOW-TO</P>
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<P STYLE="margin-bottom: 0.00cm">pppd man pages</P>
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<P STYLE="margin-bottom: 0.00cm">netdate man pages</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P STYLE="margin-bottom: 0.00cm"><B>Resources:</B></P>
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<P STYLE="margin-bottom: 0.00cm">http://www.nist.gov/</P>
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<P STYLE="margin-bottom: 0.00cm"><BR>
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</P>
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<P> <HR> <P>
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<center><H4>Previous ``Linux Primer'' Columns</H4></center>
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<p>
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<A HREF="../issue32/jenkins1.html">Linux Primer #1, September 1998</A><BR>
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<A HREF="../issue33/jenkins2.html">Linux Primer #2, October 1998</A><BR>
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<A HREF="../issue34/jenkins3.html">Linux Primer #3, November 1998</A><BR>
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<A HREF="../issue35/jenkins4.html">Linux Primer #4, December 1998</A><BR>
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<A HREF="../issue36/jenkins5.html">Linux Primer #5, January 1999</A><BR>
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<A HREF="../issue37/jenkins6.html">Linux Primer #6, February 1999</A><BR>
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<A HREF="../issue38/jenkins7.html">Linux Primer #7, March 1999</A><BR>
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<!--===================================================================-->
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<P> <hr> <P>
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<center><H5>Copyright © 1999, Ron Jenkins <BR>
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Published in Issue 39 of <i>Linux Gazette</i>, April 1999</H5></center>
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