The necessity of passwordless SSH

Users/Site Administrators
1

I’ve deployed a PBS cluster with one control node and four compute nodes. Is it mandatory to configure passwordless SSH between these five nodes? What impact will not configuring it have on my usage?

2

No for PBS , but requires some mechanism to stage-in / stage-out the data.
How about running a MPI jobs involving all these 5 nodes ?
It is a requirement to setup an HPC cluster.

  • headnode to compute node(s) and vice versa
  • compute node(s) to compute node(s)

Stage-in and Stage-out would be affected (job will be in waiting state - W state)
#PBS -W stagein=... and #PBS -W stageout=... directives

PBS use
###########################################

  • rcp - (in the remote past) - It was the default file-transfer mechanism in early legacy versions of PBS ( /etc/pbs.conf , PBS_RCP=/bin/false to avoid it )
  • scp - This is the current common standard. When moving data to or from a remote host, the execution daemon (pbs_mom) calls /bin/scp to securely copy your data (stage-in/stage-out). ( /etc/pbs.conf , PBS_SCP=/bin/scp , by default now )
  • cp - This is used if the file path is local to the host or mapped across a shared file network. Check the mom_priv/config for this $usecp directive.

for stage-in and stage-out.

3

Mr. adarsh, thank you very much for your reply. I have configured a shared directory file system for access by both the management and compute nodes, and I use #PBS -k oed for my every job. If multiple nodes are running parallel jobs like MPI, doesn’t PBS use its own data transfer mechanism (sockets)? It seems that passwordless access between nodes doesn’t need to be configured.

4

Thank you and you are right and please find the below information for clarity:

  • PBS TM (Task Manager) does not use SSH for launching or managing tasks on the allocated execution nodes.

  • PBS uses its configured file-transfer mechanism, such as scp or cp, only for file staging/copy operations where applicable.

  • If your MPI libraries are compiled and configured to use the PBS TM interface for all multi-node MPI job launches, then passwordless SSH between the compute nodes is not required.

  • Passwordless SSH is only needed when the MPI implementation or application itself uses SSH for remote process startup