[Beowulf] PVM on wireless...

Robert G. Brown rgb at phy.duke.edu
Thu Feb 7 12:55:31 EST 2008


On Wed, 6 Feb 2008, kohlja at ornl.gov wrote:

> Hey Gang!
>
> Sounds like you're having some "fun" with PVM over wireless...?  :-)
>
> (A buddy (Wael Elwasif) forwarded your discussion to me;
> please always feel free to copy "pvm at msr.csm.ornl.gov"
> with PVM inquiries when you get stuck.  I try to be
> pretty responsive, though this is all unfunded work now... :)

Bless you.

However, I've just manage to figure the problem out on my own.  It is,
after all, a firewall issue.  There are apparently different/new
defaults in Fedora 7 and 8 than I expected.  If I >>completely disable<<
the firewall it works.  This isn't really desireable, so I'll go back
and see if I can figure out how to open the minimal set of ports to make
it work.  I wasn't seeing it in my earlier tests because I was verifying
that it worked FROM a newly installed wired Fedora 8 host to my older
hosts, that happened to be wired, or to a fedora 7 or fedora 8 laptop
that wouldn't work even with the appropriate interfaces set to trusted.
When just to be thorough I tried to configure the F8 wired system from
an older F6 wired system, it failed too, which led me to try disabling
the firewall altogether.

I apologize to all those who wasted time trying to help me with
something I should have figured out on my own.  I was fooled by the
accidental appearance of order, with both my extant laptops running the
same dysfunctional firewall, and by testing connections only FROM my one
wired host running F8.  I should have just kept plugging until I tested
to and from every pair.

While I've got the One True PVM Human(s) on the line, though -- a
suggestion for PVM to help others avoid this problem in the future on
networks wired and wireless:

It would really, really help if man pvm (or man pvmd or man pvm_intro)
documented a suitable firewall setting that will let PVM function
without just turning off the firewall altogether.  There is no pvm setup
in /etc/services, for example, no pvm checkbox in the panels managed by
system-config-firewall in the latest Fedoras, no suggestion as to what
what protected port(s) or ranges one has to enable explicitly.  In fact
for once even google is failing me -- I'm not finding a lot of
documentation or remarks by ANYONE on what ports pvm needs open (besides
ssh, which obviously is open and works).  Usually as long as the
spawning of a network application itself works using an enabled
protected port (in this case, I would have expected ssh), the secondary
ports opened in unprotected space just work.  Am I wrong in this?  Do I
need to explicitly open more ports somewhere?

To find out, this leaves me with running e.g. tcpdump and watching as
pvm attempts to connect, opening port ranges one at a time and doing a
binary search, or something similarly painful.  Or just asking you.  So
what (minimal set of) ports do I need to leave open besides ssh, which
is always open on my systems anyway?

An additional suggestion would be to (if possible) have the RPM install
"fix" the port situation so that pvm shows up on system-config-firewall
and/or finish with a message to the installer that a particular firewall
setting must be installed or enabled and/or add something to the
debugging info provided by pvm so that on a timeout (in particular) it
prints something like "Unable to connect due to timeout.  Verify that
pvm is correctly installed and that port range xxxx-xxxx is open on the
target."

I actually help a lot of people get started with PVM (they write me
offline because I have a template PVM tarball up on my personal website)
and the more I know, the better I can help them...;-)

    rgb

-- 
Robert G. Brown                            Phone(cell): 1-919-280-8443
Duke University Physics Dept, Box 90305
Durham, N.C. 27708-0305
Web: http://www.phy.duke.edu/~rgb
Book of Lilith Website: http://www.phy.duke.edu/~rgb/Lilith/Lilith.php
Lulu Bookstore: http://stores.lulu.com/store.php?fAcctID=877977
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