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20010427: McIDAS ADDE functionality under RedHat 7.1 Linux (fwd)


===============================================================================
Robb Kambic                                Unidata Program Center
Software Engineer III                      Univ. Corp for Atmospheric Research
address@hidden             WWW: http://www.unidata.ucar.edu/
===============================================================================

---------- Forwarded message ----------
Date: Fri, 27 Apr 2001 22:31:29 -0600
From: Tom Yoksas <address@hidden>
To: Gilbert Sebenste <address@hidden>
Subject: 20010427: McIDAS ADDE functionality under RedHat 7.1 Linux

>From:  Gilbert Sebenste <address@hidden>
>Organization:  NIU
>Keywords:  200104280154.f3S1sSL24870 McIDAS ADDE RedHat 7.1 Linux inetd xinetd

Gilbert, et. al.,

I am not writing to jump into the Solaris vs Linux debate (although I
think that Solaris x86 runs much better than Linux, but I run Linux
at home :-), I am writing to make a small comment on McIDAS ADDE
functionality under RedHat 7.1 Linux.

Gilbert noted:

...
>BTW, McIDAS under 7.1 works
>fine, except my ADDE server suddenly stopped working from those people
>trying to get data from me. I think it's back up again...will check.

The problem that Gilbert ran into was caused by the upgrade from RedHat
6.2 Linux to 7.1.  The story is as follows:

o RedHat 6.x Linux runs inetd, and inetd is configured with /etc/inetd.conf

o RedHat 7.x Linux no longer runs inetd.  Instead, it runs xinetd, and
  xinetd uses a different approach to configuration: files in the
  /etc/xinetd.d directory

o RedHat 7.x Linux includes an executable called inetdconvert (a Python
  script) that converts /etc/inetd.conf entries to files in /etc/xinetd.d

o newer versions of Linux (and FreeBSD) include what looks like all
  registered uses of port numbers in /etc/services.  Port 500 (both TCP
  and UDP) is registered to a program called 'isakmp'.

o McIDAS ADDE uses ports 500 and 503 for communications: port 500 for
  uncompressed transfers and port 503 for compressed transfers

All of this sounds reasonably OK until one realizes that there is a
port conflict between McIDAS ADDE uncompressed data transfers and
'isakmp'.  This is easily gotten around by commenting out the 'isakmp'
entries in /etc/services and sending a USR1 signal (not a HUP) to
xinetd.

The problem, however, is that inetdconvert does NOT convert the
/etc/inetd.conf entries for ADDE services (mcserv and mccompress)
correctly.  The /etc/services entries for mcserv (port 500) and
mccompress (port 503) get deleted in the upgrade from RedHat 6.x to
7.x, AND the configuration files created in /etc/xinetd.d for those
services do NOT include the port configuration information that would
obviate the need for an entry in /etc/services.

The solution that returns ADDE functionality is the addition of a port
definition line to the /etc/xinetd.d/mcserv and /etc/xinetd.d/mccompress
files followed by the sending of a USR1 signal to xinetd (which tells
it to reread its configuration files).  After these steps were
performed on Gilbert's machine, ADDE returned to functionality.

I will be updating the Linux section of the Unidata McIDAS
'Notes and Warnings" web page:

http://www.unidata.ucar.edu/packages/mcidas/770/mcx/warnings_mcx.html 

with the steps needed to recover from the RH 6.x to 7.x upgrade later
this weekend.

Tom
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