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Subject: Re: [OMPI users] openmpi 1.6.3 fails to identify local host if its IP is 127.0.1.1
From: Ralph Castain (rhc_at_[hidden])
Date: 2013-06-26 07:38:54


The root cause of the problem is that you are assigning your host name to
the loopback device. This is rather unusual, but not forbidden. Normally,
people would name that interface something like "localhost" since it cannot
be used to communicate off-node.

Doing it the way you have could cause problems for you as programs that do
a lookup to communicate will get the loopback address when they might have
expected something else. Still, we should handle this case.

I'll see what we can do

On Wed, Jun 26, 2013 at 2:26 AM, Riccardo Murri <riccardo.murri_at_[hidden]>wrote:

> Hello,
>
> On 26 June 2013 03:11, Ralph Castain <rhc_at_[hidden]> wrote:
> > I've been reviewing the code, and I think I'm getting a handle on
> > the issue.
> >
> > Just to be clear - your hostname resolves to the 127 address? And you
> are on
> > a Linux (not one of the BSD flavors out there)?
>
> Yes (but resolves to 127.0.1.1 -- not the usual 127.0.0.1), and yes
> (Rocks 5.3 ~= CentOS 5.3).
>
>
> > If the answer to both is "yes", then the problem is that we ignore
> loopback
> > devices if anything else is present. When we check to see if the
> hostname we
> > were given is the local node, we resolve the name to the address and then
> > check our list of interfaces. The loopback device is ignored and
> therefore
> > not on the list. So if you resolve to the 127 address, we will decide
> this
> > is a different node than the one we are on.
> >
> > I can modify that logic, but want to ensure this accurately captures the
> > problem. I'll also have to discuss the change with the other developers
> to
> > ensure we don't shoot ourselves in the foot if we make it.
>
> Ok, thanks -- I'll keep an eye on your replies.
>
> Thanks,
> Riccardo
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