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Subject: Re: [OMPI users] How does authentication between nodes work without password? (Newbie alert on)
From: Tena Sakai (tsakai_at_[hidden])
Date: 2011-02-14 11:39:57

Thank you. Ashley, for clarification between sudo and su.
I live in a sphere of ignorance, but I feel I am slightly



On 2/14/11 1:39 AM, "Ashley Pittman" <ashley_at_[hidden]> wrote:

> "sudo" and "su" are two similar commands for doing nearly identical things,
> you should be running one or the other but there is no need to run both.
> "sudo -s" is probably the command you should have used. It's a very common
> mistake.
> sudo is a command for allowing you to run commands as another user, either
> using your own or no password. su is a command to allow you to run commands
> as another user using their password. What sudo su is doing is running a
> command as root which is then running a shell as root, "sudo -s" is a much
> better way of achieving the same effect.
> Ashley.
> On 13 Feb 2011, at 22:16, Tena Sakai wrote:
>> Thank you, Ashley, for your comments.
>> I do have a question.
>> I was using 'sudo su' to document the problem I am running
>> into for people who read this mailing list, as well as for
>> my own record. Why would you say I shouldn't be doing so?
>> Regards,
>> Tena
>> On 2/13/11 1:29 PM, "Ashley Pittman" <ashley_at_[hidden]> wrote:
>>> On 12 Feb 2011, at 14:06, Ralph Castain wrote:
>>>> Have you searched the email archive and/or web for openmpi and Amazon
>>>> cloud?
>>>> Others have previously worked through many of these problems for that
>>>> environment - might be worth a look to see if someone already solved this,
>>>> or
>>>> at least a contact point for someone who is already running in that
>>>> environment.
>>> I've run Open MPI on Amazon ec2 for over a year and never experienced any
>>> problems like the original poster describes.
>>>> IIRC, there are some unique problems with running on that platform.
>>> None that I'm aware of.
>>> EC2 really is no different from any other environment I've used, either real
>>> or virtual, a simple download, ./configure, make and make install has always
>>> resulted in a working OpenMPI assuming a shared install location and home
>>> directory (for launching applications from).
>>> When I'm using EC2 I tend to re-name machines into something that is easier
>>> to
>>> follow, typically "cloud[0-15].ec2" assuming I am running 16 machines, I
>>> change the hostname of each host and then write a /etc/hosts file to convert
>>> from hostname to internal IP address. I them export /home from cloud0.ec2
>>> to
>>> all the other nodes and configure OpenMPI with --prefix=/home/ashley/install
>>> so that the code is installed everywhere.
>>> For EC2 Instances I commonly use Fedora but have also used Ubuntu and
>>> Solaris,
>>> all have been fundamentally similar.
>>> My other tip for using EC2 would be to use a persistent "home" folder by
>>> renting a disk partition and attaching it to the first instance you boot in
>>> a
>>> session. You pay for this by Gb/Month, I was able to use a 5Gb device which
>>> I
>>> mounted at /home in cloud0.ec2 and NFS exported to the other instances,
>>> again
>>> at /home. You'll need to add "ForwardAgent yes" to your personal
>>> .ssh/config
>>> to allow you to hop around inside the virtual cluster without entering a
>>> password. The persistent devices are called "Volumes" in EC2 speak, there
>>> is
>>> no need to create snapshots unless you want to share your volume with other
>>> people.
>>> Ashley.
>>> Ps, I would recommend reading up on sudo and su, "sudo su" is not a command
>>> you should be typing.
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