[Beowulf] PVM on wireless...

kohlja at ornl.gov kohlja at ornl.gov
Fri Feb 8 11:15:26 EST 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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