Using screen on the Cluster

Created by: Gina Yu

Last Updated: July 30,2026

screen is a terminal utility that allows you to keep terminal sessions running in the background, even after you disconnect from the cluster, close your terminal, or lose your SSH connection.

screen can be used to:

  • Keep commands running in the background
  • Run long-running jobs or scripts
  • Maintain remote terminal sessions
  • Monitor interactive analyses over time
  • Return to the same terminal session at a later time
  • Organize multiple terminal sessions simultaneously

This page assumes that you are already familiar with logging into the cluster through SSH. For a broader introduction to cluster computing, please see the Cluster Computing page.

Screen terminology:

A screen session can have one of two states:

  • Attached — You are currently connected to the session.

  • Detached — The session is still running, but no terminal is currently connected to it.

Detached sessions continue running until they are explicitly terminated. A detached session is still active and any programs running inside it will continue executing.

Quick Reference

The table below summarizes the most commonly used screen commands.

Task Command
Start a new session screen
Start a named session screen -S my_session
List active sessions screen -ls
Reattach to a session screen -r my_session
Force reattach to a session screen -d -r my_session
Kill a session screen -S my_session -X quit
Detach from a session Ctrl + A, then D

Starting a screen Session

First, SSH into the Takim2 cluster

ssh yourPennKey@takim2

Replace yourPennKey with your actual PennKey.

After logging in, your terminal should look similar to:

yourPennKey@takim2 ~$

To start a new screen session, simply type:

screen

Alternatively, you can create a named session, which is recommended if you plan to have multiple sessions:

screen -S my_session

Working Inside a screen Session

Once inside a screen session, you can use the terminal just as you normally would after logging into the cluster.

For example, you can:

  • Start an interactive R session by typing R
  • Run scripts such as Rscript analysis.R or python script.py
  • Navigate directories using commands such as cd my_project
  • Submit jobs using bsub
  • Monitor log files or other running processes

Think of a screen session as a terminal that remains active even after you disconnect.

Note: screen does not provide additional computing resources. It simply keeps your terminal session alive. For computationally intensive jobs requiring specific CPU or memory resources, use the cluster scheduler with bsub.

To leave a screen session without stopping the commands running inside it, press:

Ctrl + A, then D

This detaches the session while allowing any running commands to continue executing in the background.

Managing Existing screen Sessions

To view all active screen sessions, type:

screen -ls

The output will look similar to:

123456.pts-2.takim2 (Detached)

where:

  • 123456 is the session ID.
  • (Detached) indicates that the session is still running in the background.

To reconnect to a session, type:

screen -r 123456

or, if you named your session:

screen -r my_session

To permanently end a session, type:

screen -S 123456 -X quit

or simply type exit from within the session.

If multiple screen sessions are active, the output may look similar to:

Example output:

There are screens on:
    123456.analysis    (Detached)
    987654.testing     (Detached)

2 Sockets in /run/screen/S-yourPennKey.

Best Practices

To keep your workspace organized, it is recommended to remove screen sessions that are no longer needed.

Unused sessions can:

  • Continue running programs that consume CPU, memory, or other cluster resources
  • Create clutter by accumulating detached sessions
  • Make it more difficult to identify active work when using screen -ls

Using descriptive session names (e.g., screen -S simulation) can also make it easier to manage multiple sessions.

Example Workflow

ssh yourPennKey@takim2
screen -S analysis
R

Run your analysis as usual.

When you want to disconnect without stopping your work:

  • Press Ctrl + A, then D

Later, reconnect by logging back into the cluster and running:

screen -r analysis

Troubleshooting

Recovering After a Disconnect

If your internet connection drops or you accidentally close your terminal, your screen session will continue running on the cluster.

Simply reconnect to the cluster using SSH:

ssh yourPennKey@takim2

Then list your available sessions:

screen -ls

Finally, reconnect to your session:

screen -r my_session

Session Already Attached

If screen reports that a session is already attached, you can force it to detach from the previous terminal and reconnect to your current one:

screen -d -r my_session

Managing Existing Sessions

To terminate the current screen session from within the session itself, simply type:

exit

In Summary

screen is especially useful for interactive work where you expect to reconnect later. For non-interactive analyses or jobs requiring substantial computational resources, submitting a job through the cluster scheduler (bsub) is generally the preferred approach.