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Set up RCC on a Mac

This checklist uses Terminal and the OpenSSH client included with current macOS. Allow about 15 minutes after your RCC account and approved connection settings are available.

1. Check the built-in SSH client

Open Terminal from Applications → Utilities, then run:

ssh -V

A line beginning with OpenSSH means the client is ready. Keep macOS patched; do not replace the system client merely because another tutorial uses a different package manager.

2. Create one RCC key

If you do not already have a dedicated RCC key, run:

mkdir -p ~/.ssh
chmod 700 ~/.ssh
ssh-keygen -t ed25519 -f ~/.ssh/id_rcc

Use a strong passphrase. ~/.ssh/id_rcc is private and stays on this Mac. ~/.ssh/id_rcc.pub is public and is the only key file you register with RCC.

Display the public key when the account form asks for it:

cat ~/.ssh/id_rcc.pub

3. Add the approved RCC configuration

Open the SSH configuration in the simple terminal editor:

nano ~/.ssh/config

Paste this configuration and replace YOUR_RCC_USERNAME with your RCC username. login.ikim.uk-essen.de is the RCC jump host; it only forwards your connection to the shell host:

Host rcc-login login.ikim.uk-essen.de
    HostName login.ikim.uk-essen.de
    User YOUR_RCC_USERNAME
    IdentityFile ~/.ssh/id_rcc
    IdentitiesOnly yes
    ForwardAgent no

Host shellhost c? c?? c??? d?? g?-? g?-??
    HostName %h.ikim.uk-essen.de
    User YOUR_RCC_USERNAME
    IdentityFile ~/.ssh/id_rcc
    IdentitiesOnly yes
    ProxyJump rcc-login
    ForwardAgent no

Replace only the values identified by the approved RCC instructions. Save in nano with Control-O, Return, then exit with Control-X. Protect the file:

chmod 600 ~/.ssh/config ~/.ssh/id_rcc

The first block describes the jump host. The second describes the shell host you actually use. You do not log into the jump host; ProxyJump forwards the connection automatically.

The stable service model is login.ikim.uk-essen.de as the forwarding-only public doorway and shellhost (shellhost.ikim.uk-essen.de) as the ordinary shell and SSH file-transfer endpoint. The login tier is not a /homes, /groups, or /projects endpoint.

To see that distinction without relying on aliases, a file copy looks like:

scp -J YOUR_RCC_USERNAME@login.ikim.uk-essen.de YOUR_RCC_USERNAME@shellhost.ikim.uk-essen.de:/groups/<group>/demo.test1 .

Here login.ikim.uk-essen.de supplies only the jump path; shellhost: is the remote data endpoint. SFTP and rsync use the same separation.

4. Check, then connect once

Inspect the effective settings without connecting:

ssh -G shellhost

Verify the approved server identity through the institutional instructions, then make one connection attempt:

ssh shellhost

Stop if SSH reports an unexpected host-key change. Do not delete all known_hosts entries or disable host-key checking.

5. Add VS Code only after Terminal works

For most users, VS Code with Microsoft's Remote - SSH extension is the easiest day-to-day editor. Follow the dedicated VS Code with RCC section and select shellhost as the destination. VS Code uses the same configuration and cannot repair an SSH connection that fails in Terminal.

Use the shell host to edit code, use Git, submit jobs, inspect logs, and access authorized shared files. Submit computation through Slurm.

If you want the guided course

Download and extract RCC Expedition, then open START HERE.html. Choose Open the course now; installing a Desktop shortcut is optional.

Continue with your first 15 minutes or the full access reference.