old-www/HOWTO/Remote-Serial-Console-HOWTO/bugs-reboot.html

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>A.4. Modem hangs up upon reboot</H1
><P
>During reboot the serial controller is reset. This drops the
modem control line Data Terminal Ready. This in turn instructs the
modem to hang up.</P
><P
>Avoid the temptation to configure the modem to ignore
<SPAN
CLASS="ACRONYM"
>DTR</SPAN
>. This leads to a worse bug, where the
telephone line does not clear down correctly, the modem is engaged,
and there is no way to clear it. Ignoring <SPAN
CLASS="ACRONYM"
>DTR</SPAN
>
also gives no way to clear hostile callers from the line.</P
><P
>You may wish to record the amount of time that the computer
takes from <TT
CLASS="COMPUTEROUTPUT"
>Restarting system</TT
> to
the boot loader prompt.</P
><P
>The modem may also hang up during the boot process (as the
serial chip is reset) or when the <SPAN
CLASS="APPLICATION"
>init</SPAN
>
run level is changed (as <SPAN
CLASS="APPLICATION"
>getty</SPAN
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restarted).</P
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