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# Quick Start Guide: Launching an Interactive Desktop on an HPC Cluster with Open OnDemand

## What is Open OnDemand?

Open OnDemand is a web-based interface that provides access to HPC cluster resources through a browser. It allows you to launch interactive desktop sessions, run applications, manage files, and submit jobs without using the command line.

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# Launching an Interactive Desktop Session

## 1. Log In

Open your cluster’s Open OnDemand URL in a web browser and sign in with your HPC credentials.

Typical login page methods include: - Institution SSO - Username/password - Multi-factor authentication

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## 2. Open the Interactive Apps Menu

After logging in:

1. Locate the Interactive Apps menu at the top of the page. 2. Select the desired desktop environment, such as:

1. Interactive Desktop
2. Remote Desktop
3. XFCE Desktop
4. GNOME Desktop

(The exact names vary by cluster.)

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## 3. Configure the Job

You will be presented with a job submission form.

Typical options include:

Choose resources appropriate for your workload.

Example: - 4 CPU cores - 8 GB RAM - 2-hour wall time

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## 4. Launch the Session

Click:

- Launch - Submit - or Start

depending on your site configuration.

The job will enter the scheduler queue.

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## 5. Wait for the Job to Start

Your session status will typically show: - Queued - Starting - Running

Once the job starts, a button such as Launch Desktop or Connect to Desktop will appear.

Click it to open the remote desktop in your browser.

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## 6. Use the Desktop Environment

Inside the desktop session, you can: - Open terminals - Run GUI applications - Use IDEs - Visualize data - Launch MATLAB, RStudio, ParaView, etc.

The session behaves similarly to a Linux desktop computer running on the cluster.

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# File Access

You can transfer and manage files using: - The Files menu in Open OnDemand - SCP/SFTP - Shared storage mounted on the cluster

Your home directory and project storage are typically available automatically.

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# Ending the Session

When finished:

1. Save your work. 2. Close applications. 3. Return to the Open OnDemand dashboard. 4. Select My Interactive Sessions. 5. Click Delete or Terminate to end the job.

Closing the browser tab alone may not stop the job.

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# Troubleshooting

## Job Stays Queued

Possible causes: - Cluster is busy - Requested resources are too large - Incorrect account or partition

Try reducing: - CPU count - Memory - Wall time

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## Desktop Will Not Open

Possible causes: - Browser popup blocker - Expired session - VNC/websocket startup failure

Try: - Refreshing the page - Relaunching the job - Using a different browser

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## Session Disconnects

Interactive jobs automatically terminate when: - Wall time expires - The job is canceled - Cluster maintenance occurs

Save work frequently.

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# Best Practices

- Request only the resources you need. - Use shorter wall times when possible. - Terminate unused sessions promptly. - Use interactive desktops for visualization and development, not large batch production runs.