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Subject: Re: [OMPI users] How does authentication between nodes work without password? (Newbie alert on)
From: Ashley Pittman (ashley_at_[hidden])
Date: 2011-02-14 04:39:05


"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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-- 
Ashley Pittman, Bath, UK.
Padb - A parallel job inspection tool for cluster computing
http://padb.pittman.org.uk