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Subject: Re: [OMPI docs] Behavior of --host and --hostfile flags on mpirun
From: Jeff Squyres (jsquyres) (jsquyres_at_[hidden])
Date: 2013-10-11 16:10:14


Also, it's more common to use a hostfile *or* the --host option. It's fairly uncommon to use both.

As to whether one should use FQDN or a basename, it doesn't matter to MPI. If the system resolves the name, OMPI can use it.

Finally, a point that is worth noting (because so many people make the wrong assumption): the hostnames that are listed in the hostfile or --host option have nothing to do with what network interfaces are used for MPI traffic. The hosts specified by the hostfile (or --hosts) are *only* used to determine on which nodes MPI processes are launched. The determination of which network interfaces are used are controlled by other MCA parameters (e.g., the "btl" MCA parameter, and various mca_btl_*_if_include / mca_btl_*_if_exclude MCA parameters).

On Oct 11, 2013, at 1:57 PM, Kelly Black <kjblack_at_[hidden]> wrote:

> Dear Shao-Ching,
>
> oops, I see what you mean. Sorry, I got sloppy and in a hurry. I should have the slots= flag in that file.
>
> Sincerely,
> Kel
>
> _______________________________________________________
> Kelly Black Phone: (315) 600-8334
> Clarkson University Fax: (315) 268-2371
> Department of Math. & C.S.
> PO Box 5815
> Potsdam, NY 13699-5815
> USA
>
>
> On Fri, Oct 11, 2013 at 1:54 PM, Kelly Black <kjblack_at_[hidden]> wrote:
> Hello,
>
> I thought that the "slots" flag was optional in the host file format where the slots option gives the max no. of slots?
>
> -Kel
>
> _______________________________________________________
> Kelly Black Phone: (315) 600-8334
> Clarkson University Fax: (315) 268-2371
> Department of Math. & C.S.
> PO Box 5815
> Potsdam, NY 13699-5815
> USA
>
>
> On Fri, Oct 11, 2013 at 1:24 PM, Shao-Ching Huang <huangsc_at_[hidden]> wrote:
> Kel:
>
> I believe the ompi hostfile format is:
>
> # myhosts.txt
> thingOne.clarkson.edu slots=4
> thingTwo.clarkson.edu slots=4
>
> Shao-Ching
>
>
> On Fri, Oct 11, 2013 at 10:21 AM, Ralph Castain <rhc_at_[hidden]> wrote:
> I *think* that should work, but I haven't personally tested it.
>
> On Oct 11, 2013, at 9:27 AM, Kelly Black <kjblack_at_[hidden]> wrote:
>
>> Hello,
>>
>> I have a question about the --host and --hostfile flags used by mpirun. Do you have to use fully qualified host names in the arguments to the --host option if the fully qualified domain name is given in the host file?
>>
>> For example, if I have a host file like this:
>>
>> # myhosts.txt
>> thingOne.clarkson.edu=4
>> thingTwo.clarkson.edu=4
>>
>> Can I then use the following command?
>>
>> mpirun --hostfile myhosts.txt --host thingOne -np 3 bubba
>>
>> Sincerely,
>> kel
>> _______________________________________________________
>> Kelly Black Phone: (315) 600-8334
>> Clarkson University Fax: (315) 268-2371
>> Department of Math. & C.S.
>> PO Box 5815
>> Potsdam, NY 13699-5815
>> USA
>> _______________________________________________
>> docs mailing list
>> docs_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/docs
>
>
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-- 
Jeff Squyres
jsquyres_at_[hidden]
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