[Beowulf] PVM on wireless...
kohlja at ornl.gov
kohlja at ornl.gov
Fri Feb 8 08:15:26 PST 2008
Awesome Strangelove Reference...! :-D
"I Have A Plan...!" :-)
Yep, I am now getting inundated with people having rsh/ssh problems
with PVM, so a higher power clearly wants me to better document this.
Thanks Much, Will Do... :)
Jeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeem ;)
On Fri, Feb 08, 2008 at 05:35:31AM -0500, Robert G. Brown wrote:
> On Thu, 7 Feb 2008, kohlja at ornl.gov wrote:
>> I admit this may be an antiquated cynical mentality, and I
>> further concur that PVMNETSOCKPORT is an obvious omission
>> in the basic documentation/faq...
> As they say, you can't RTFM if there ain't no FM... (or if the solution
> exists but isn't there).
> One is reminded of Dr. Strangelove, where the president (Peter Sellers)
> has just learned that if the maverick B52 piloted by Slim Pickens gets
> through, a doomsday device that is supposed to deter first nuclear
> strikes will go off that will destroy the world. Unfortunately, the
> Soviet Union didn't actually tell us that it was built. Dr.
> Strangelove (Peter Sellers), after musing for a moment on the brilliance
> of the concept, turns and says in an increasingly shrill voice:
> But...the whole point of the Doomsday Machine...is lost...if you keep
> it a SECRET. Why didn't you tell the world, eh?
> Hmmm...;-)
> rgb
>> Thanks for your suggested text! (And the suggestion to
>> enhance our coverage of rsh/ssh usage... :-)
> Ya, well. Just now finished telling the umptieth would-be PVM user how
> to go about it in an email message, augmenting further online docs such
> as this one:
> http://www.uow.edu.au/~suresh/web/cfamily/pvm.html
> which is actually pretty decent, although I generally use the ssh
> default dsa instead of rsa since on linux boxes it invariably works.
> But better than forcing each user to employ google to snarf out
> solutions to each problem they encounter, how much better to write a
> really nice "Getting Started with PVM" or perhaps better still, a "PVM
> HOWTO" on tldp.org. Publish there, and be sure to include a copy in
> plain sight in /usr/share/pvm3/PVM_HOWTO.
> Truthfully, good documentation, especially a walkthrough tutorial on
> getting started (including sample code or links to sample code) that
> takes a would-be user from "yum install pvm\*" to executing a Real
> Parallel Program (however trivial) on a two node cluster would really
> encourage the use of the library. Adding a bit more (such as a PVM
> program development template) would be only icing on the cake, so to
> speak.
> If I had the time I'd write it myself. I've already got a project_pvm
> program template up on the web, but it is sadly underdocumented through
> the setup of PVM itself.
> rgb
>>
>> All the Best,
>>
>> Jeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeem ;)
>>
>> On Thu, Feb 07, 2008 at 04:42:21PM -0500, Robert G. Brown wrote:
>> >> > 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?
>> >>
>> >> Ah Yes. O.K., so I wish it was that simple, but alas PVM can use as
>> >> many ports as you have machines in your cluster, or could use just 1.
>> :-}
>> >>
>> >> Normally, the master pvmd creates/accepts connections over a small
>> >> set of ports, possibly 1, but if PvmRouteDirect is enabled in a PVM
>> >> application, then a myriad of direct-connection socket links are
>> >> created, to link whichever machines the local PVM application tasks
>> >> communicate with, on a demand-driven basis...
>> >>
>> >> So it's not generally possible to specify an explicit "range" of
>> ports.
>> >> However, it _is_ possible to set the "starting" port for this
>> collection,
>> >> using the aforementioned "$PVMNETSOCKPORT" environment variable.
>>
>> > OK, I'm giving this a try. Although I'd have to ask why pvmd doesn't
>> do
>> > the fork thing and clone a single open port on which it listens into a
>> > dynamically allocated port that inherits from the open one. In
>> > principle one only needs a single port to be open to connect to pretty
>> > much any network based application, or so I had thought. At least, I
>> do
>> > that in xmlsysd and never have to punch more than one porthole through
>> a
>> > firewall.
>>
>> > Hmmm, it's working sort of -- looks like I need to open UPD ports,
>> > right, not TCP? Having trouble on one host where I've punched the hole
>> > but didn't >>locally<< set PVMNETSOCKPORT to match, so I'm trying again
>> > with the local environment variable set.
>>
>> > Yup, that works.
>>
>> > So I'm guessing that pvmd reads it as it starts up wherever. Why does
>> > it need to do this on a client? Can't the port(s) be passed from the
>> > master when it starts up pvmd?
>>
>> >> This sets the first port that PVM will try to use, and all subsequent
>> >> ports will usually be consecutive positive increments of that starting
>> >> port (i.e. PVMNETSOCKPORT++... :-).
>> >>
>> >> So in most cases, you could probably plan on opening up a 100 or 1000
>> >> ports _somewhere_ in your firewall, depending on your needs, and then
>> >> just tell PVM where to start, using $PVMNETSOCKPORT...
>> >>
>> >> I've always considered this solution a bit of a kludge, which is why
>> >> it doesn't show up in the man pages, but if it works well enough to
>> >> save people lots of hassle, then I can add some commentary on it...?
>>
>> > Kludge or not, how can you have an environment variable in an
>> > application and not provide knowledge of it or instructions on its use
>> > in the man page? Something like:
>>
>> > PVM requires open ports on target hosts to function. Many hosts are
>> > installed with strong firewall rules by default. If you install pvm
>> on
>> > a slave and pvm appears to hang when you attempt to add it, eventually
>> > timing out without success, consider adding the following to your
>> local
>> > personal or system environment (in, for example, ~/.bash_profile on
>> all
>> > hosts):
>>
>> > PVMNETSOCKPORT=10000
>> > export PVMNETSOCKPORT
>>
>> > Then configure your firewall(s) to open a range of udp ports starting
>> > at this value, such as 10000-11024 (which need be any larger than the
>> > largest number of machines you expect to have in your virtual
>> machine).
>>
>> > However a better solution still is to have the daemon fork on a single
>> > "permanent" port address > 1024, e.g. 10000, and get a negotiated
>> > connection in the upper (non-protected) port space that way.
>>
>> >> It may depend on the firewall settings, but a nice "Connection
>> >> Refused" would usually go a long way toward diagnosing things,
>> >> whereas the more secure firewall alternative of simply
>> >> "no response" would only result in a "timed out" PVM message...
>> >>
>> >> I'm open to suggestions on ways to identify or diagnose the
>> problem...!
>>
>> > As I said, document EVERYTHING in the man page(s). It is what it is
>> for.
>> > Lots of users do, in fact, RTFM but get frustrated and give up when
>> they
>> > try something and it just doesn't work and they can't see why.
>>
>> > On the same line, a perennial problem with PVM is getting it to work
>> > with rsh and ssh. In fact, half the problems I help people with who
>> > randomly write me is getting it to work with one or the other. The
>> > internal diagnostics are certainly very helpful, at this point, but it
>> > would also be worth adding a new man page like pvm_rsh that does
>> nothing
>> > but walk users through the ritual of setting PVM_RSH and establishing
>> > appropriate e.g. ssh keys.
>>
>> > Just a thought or two.
>>
>> > rgb
>>
>> >>
>> >> Thanks Much for your interest and feedback!
>> >>
>> >> All the Best,
>> >>
>> >> Jeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeem ;)
>> >>
>> >> > 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
>> >>
>> >>
>> (:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:
>> >>
>> >> James Arthur "Jeeembo" Kohl, Ph.D. "Da Blooos Brathas?! They
>> >> Oak Ridge National Laboratory still owe you money,
>> Fool!"
>> >> kohlja at ornl.gov
>> >> http://www.csm.ornl.gov/~kohl/ Long Live Curtis Blues!!!
>> >>
>> >>
>> :):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):)
>> >>
>>
>> > --
>> > 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
>>
> --
> 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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