ssh directly into a specific node on a cluster, without first ssh into login node?

Question

I usually log on to a cluster, start a slurm interactive job, then I am able to ssh into specific running nodes.

• My questions is, is it generally possible to ssh into a specific node from my local machine, without first ssh-ing into a login node? I am a user and not an admin.

My purpose of doing this is I would like to eventually remotely debug my code using gdb (with tramps), which I am so far unable to do with windowed emacs. Another alternative I can think of is to start a emacs X gbd interactive session with ssh -X followed by srun.

Answer 1

There are a number of things that could prevent you from being able to ssh from your local machine, into a specific node (which I'll refer to as a compute node). I'll list the configurations which over the years I've seen implemented (or in the case of the PAM module - read about).

1. In some clusters, there may be network routing restrictions that would prevent your local machine from reaching a compute node. It's not unusual for login nodes to be more accessible from the network than a compute node is.
2. There may be network security devices (e.g. firewall or packet filter) in place to isolate compute nodes.
3. The base operating system on the compute nodes may have the SSH server configured so it does not allow regular users to connect. E.g. via the /etc/security/access.conf file on a Linux compute node.
4. The SSH server on the compute node may implement SLURM's PAM module that only allows users with jobs on the node to SSH into the node. This in turn has an option to only allow ssh connections that come from a node, such as a login node, that is part of the cluster.

It's also possible that none of these restrictions are in place. I'm not sure which is the most common SLURM cluster configuration.