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I managed to log in to cshpc (with an SSH key) but get asked for a password when continuing to a cluster frontend

The explanation is rather simple: the dialog server cshpc does not know any SSH (private) key from you, thus, fails to do SSH key-based authentication when connecting to one of the cluster frontends and, thus. tries password authentication as fallback.

There are a couple of solutions to mitigate that:

  1. Use the “jump host”/”proxy jump” feature of SSH and directly connect to the cluster frontends through the dialog server cshpc. To do this, either use the command line option “-j” of recent SSH versions or use an ~/.ssh/config file on your local computer. See https://hpc.fau.de/systems-services/documentation-instructions/ssh-secure-shell-access-to-hpc-systems/#ssh_config_hpc_portal for templates.
  2. Create an additional SSH key pair on cshpc and add the corresponding SSH public key to the HPC portal (if your account is already managed trough the HPC portal) – or add it to ~/.ssh/authorized_keys (which will only be a temporary solution until all HPC accounts are migrated to the HPC portal)
  3. Use an SSH agent on your local computer and allow it to forward its connection to our dialog server cshpc.

All there ways make sure that cshpc has a SSH private key available when connecting to the cluster frontends.