Connecting to the Cluster

There are two ways to access ARC clusters: SSH (command line) and Open OnDemand (web interface).

Method 1: SSH (Command Line)

Connect to your specific cluster using its generic login node.

ssh username@orion-login.hpc.msstate.edu

ssh username@hercules-login.hpc.msstate.edu

ssh username@ptolemy-login.arc.msstate.edu

ssh username@atlas-login.hpc.msstate.edu

ssh username@morrill-login.hpc.msstate.edu

Linux/macOS

Open a terminal and connect using the command for your cluster above.

Windows

Option A: PowerShell/CMD

Open a command prompt or powershell, then use the cluster-specific ssh command above.

Option B: PuTTY

  1. Download and install PuTTY

  2. Host: Use your login node above

  3. Port: 22

  4. Click “Open”

  5. Login with your credentials


Note

Only the Login and DTN Nodes are accessible outside the ARC network.

Method 2: Open OnDemand (Web Interface)

  1. Navigate to: https://orion-ood.hpc.msstate.edu

  2. Login with your credentials

  3. Access:

    • Dashboard - Overview and job submission

    • Files - Browse and transfer files

    • Shell - Terminal in browser

    • Jobs - Manage SLURM jobs

    • Apps - Run Interactive Apps such as Jupyter and VSCode

  1. Navigate to: https://hercules-ood.hpc.msstate.edu

  2. Login with your credentials

  3. Access:

    • Dashboard - Overview and job submission

    • Files - Browse and transfer files

    • Shell - Terminal in browser

    • Jobs - Manage SLURM jobs

    • Apps - Run Interactive Apps such as Jupyter and VSCode

  1. Navigate to: https://ptolemy-ood.arc.msstate.edu

  2. Login with your credentials

  3. Access:

    • Dashboard - Overview and job submission

    • Files - Browse and transfer files

    • Shell - Terminal in browser

    • Jobs - Manage SLURM jobs

    • Apps - Run Interactive Apps such as Jupyter and VSCode

  1. Navigate to: https://atlas-ood.hpc.msstate.edu

  2. Login with your credentials

  3. Access:

    • Dashboard - Overview and job submission

    • Files - Browse and transfer files

    • Shell - Terminal in browser

    • Jobs - Manage SLURM jobs

    • Apps - Run Interactive Apps such as Jupyter and VSCode

  1. Navigate to: https://morrill-ood.hpc.msstate.edu

  2. Login with your credentials

  3. Access:

    • Dashboard - Overview and job submission

    • Files - Browse and transfer files

    • Shell - Terminal in browser

    • Jobs - Manage SLURM jobs

    • Apps - Run Interactive Apps such as Jupyter and VSCode

See Open OnDemand for more details.

First Login

After logging in, feel free to familiarize yourself with the system. See Linux Basics

# check files
ls

# check the queue
squeue

SSH Configuration (Optional)

Note

These configurations should be performed on your client, not on the clusters.

Simplify Connections

Create ~/.ssh/config for easier access:

Host orion
	HostName orion-login.hpc.msstate.edu
	User your_netid

Host hercules
	HostName hercules-login.hpc.msstate.edu
	User your_netid

Host ptolemy
	HostName ptolemy-login.arc.msstate.edu
	User your_netid

Host atlas
	HostName atlas-login.hpc.msstate.edu
	User your_netid

Host morrill
	HostName morrill-login.hpc.msstate.edu
	User your_netid

Advanced Configuration

Click to Expand

Avoid Repeated 2FA with SSH ControlMaster

By default, SSH requires authentication (password + 2FA) each time you connect. SSH ControlMaster keeps a persistent connection that can be reused, eliminating repeated authentication.

What is ControlMaster?

ControlMaster creates a master connection that binds to a Unix socket. Subsequent SSH connections reuse this socket instead of creating new connections, so you only authenticate once per session.

Setup

Run the following commands to configure SSH ControlMaster:

# Create socket directory
mkdir -p ~/.ssh/sockets

# Add ControlMaster configuration to SSH config
cat > ~/.ssh/config << 'EOF'
Host *
    GSSAPIAuthentication no
    ControlMaster auto
    ControlPath ~/.ssh/sockets/ssh_mux_%h_%p_%r
    ControlPersist 2h
    ServerAliveInterval 60
    ServerAliveCountMax 10
EOF

How It Works

  1. First connection: You authenticate normally (password + 2FA)

  2. Subsequent connections: Reuse the existing connection—no authentication needed

  3. Connection expires: After 2 hours of inactivity (configurable via ControlPersist)

Benefits

  • No repeated 2FA prompts during active sessions

  • Faster connection times

  • Reduced authentication overhead

  • Works with multiple terminal sessions simultaneously

Troubleshooting

If connections fail, check that the socket directory exists:

ls -la ~/.ssh/sockets/

To close all persistent connections manually:

ssh -O exit all

Security Tips

  • Never share your password

  • Lock your terminal/screen when stepping away