Scyld, local access to nodes, and master node as compute node

[Sean Dilda]

On Thu, 24 May 2001, Brian C Merrell wrote:

> I'm using Scyld Linux on a 24 node cluster.  Everything installed fine,
> and I'm fairly happy with it so far; beowulf has come a long way since I
> last played with it about two years ago.  But I have a few questions on
> how to set some things up.
> 
> 1) How can I get access to a specific node?  Some of the researchers I'm
> supporting want to use only part of the cluster at a time (so that other
> chunks are free for use, I suppose).  How can they access a specific node
> and run programs from it?  There doesn't appear to be any rlogind (or rsh,
> or telnet, or even a local /etc/passwd file, or ...) to accept
> connections.  bpsh won't give me a shell, so that won't work.

You do this through bpsh.  The slave nodes are to run compute jobs, not
interactive login sessions, so you really shouldn't need to run an
interactive shell on them.  If you need to do some admin work that
requires you to run stuff on the slave nodes, you can always bpsh all
the individual commands to the slave node.

> 
> 2) How can I use the master node as an active compute node (node0)?
> Running bpslave 192.168.1.1 2223 (so from the master to the master)
> doesn't seem to work, although maybe I'm really misunderstanding how this
> is supposed to work?

What are you using to run your jobs?  If you're using MPI, the rank == 0
job is always run on the master node (unless you give mpirun the
-nolocal option)

> 
> 3) While I'm at it, a few other things: is it possible to define hostnames
> for the nodes?  Obviously the master is a (mostly) normal installation
> that I can add to the hosts file or use DNS, but what about the slave
> nodes?  We'd like to have it so the master is l001 and the slaves are l002
> through l024 (that first character is a lowercase 'L', BTW).

This is handled through a program called beonss.  It assigns the master
node to be master or .-1, and all ther other nodes are .<number>   So
node 0 is .0, node 1 is .1, etc.   Can you change your programs to use
this?  If not, beonss is a fairly simple C program that shouldn't be too
difficult to modify.
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