How to Use the screen Command for Terminal Sessions

The screen command is a terminal multiplexer that allows you to manage multiple terminal sessions within a single window. It is particularly useful for managing long-running processes or remote sessions because it lets you disconnect from a session and reconnect later without disrupting the processes.

Key Features of screen

• Run multiple terminal sessions simultaneously.
• Detach from a session and reconnect later.
• Preserve long-running processes even after disconnecting from SSH.
• Split the terminal window into multiple regions.
• Scrollback buffer to review previous output.

Installing screen

On Linux

For most Linux distributions, screen is available in the default package manager:

• Ubuntu/Debian:

  sudo apt install screen

• CentOS/RHEL:

  sudo yum install screen

• Fedora:

  sudo dnf install screen

On macOS

screen comes pre-installed on macOS. You can verify by typing:

screen --version

On Windows

While screen is not natively available for Windows, you can use it through a WSL (Windows Subsystem for Linux) environment or a Unix-like terminal such as Cygwin.

Basic Usage of screen

1. Start a New Screen Session

To start a new session:

screen

This opens a new terminal window within screen.

To name the session for easier management:

screen -S session_name

2. Detach from a Session

To detach from the current screen session without ending it:

Ctrl-a d

You will return to the original terminal, but the session continues to run in the background.

3. List Active Sessions

To view all active screen sessions:

screen -ls

Example output:

There are screens on:
    1234.session_name (Detached)
    5678.another_session (Detached)
2 Sockets in /run/screen/S-username.

4. Reattach to a Session

To reattach to a specific session:

screen -r session_name

If there is only one session, you can simply type:

screen -r

5. End a Session

To terminate a session, reconnect to it and type:

exit

This will close the session and its processes.

Advanced Usage of screen

1. Splitting the Screen

Split the terminal window horizontally:

Ctrl-a S

Move between regions:

Ctrl-a Tab

To create a new shell in the active region:

Ctrl-a c

2. Naming Windows

Assign a name to a specific window for better organization:

Ctrl-a A

Type the desired name and press Enter.

3. Scrolling Back

To enable scrolling within a session:

Ctrl-a Esc

Use the arrow keys to navigate and press q to exit scrollback mode.

4. Logging Output

Save the session’s output to a log file:

Ctrl-a H

The log will be saved in the current directory as screenlog.0.

5. Locking a Session

To lock a screen session:

Ctrl-a x

You will need to enter your user password to unlock it.

Common screen Commands

Command	Description
Ctrl-a c	Create a new window
Ctrl-a n	Switch to the next window
Ctrl-a p	Switch to the previous window
Ctrl-a d	Detach from the session
Ctrl-a k	Kill the current window
Ctrl-a A	Rename the current window
Ctrl-a S	Split the terminal horizontally
Ctrl-a X	Close the current split region

Practical Use Cases

1. Long-Running Scripts: Run a script or process that might take hours, and detach from the session while it continues to run.

   screen -S long_process
   python script.py
   Ctrl-a d

   Reconnect later to check progress:

   screen -r long_process

2. Remote Sessions: Use screen during SSH sessions to ensure processes are not interrupted by connection drops.
3. Multiple Terminal Windows: Manage different tasks, such as monitoring logs, running scripts, or editing files, all within a single terminal window.

Conclusion

The screen command is a versatile tool for managing terminal sessions efficiently. Its ability to detach and reattach to sessions makes it indispensable for remote work and long-running tasks. By mastering the commands and features outlined above, you can significantly improve your productivity in terminal-based workflows.