What is Screen

screen is a Linux program that can be used to to create several virtual terminals running different processes from a single terminal window, or in the case of the HPC, a single ssh connection. This makes it easy to manage multiple detached, long-running jobs (e.g., rsync commands).

Using Screen with the HPC Cluster

Why you should use it

When your wifi cuts out and jobs fail, you can reattach your jobs back to terminal through the screen program. Generally speaking, there are 4 advantages to using screen. It enables you to:

Use multiple shell windows from a single SSH session.
Keep a shell active even through network disruptions.
Disconnect and re-connect to a shell sessions from multiple locations.
Run a long running process without maintaining an active shell session.

Where to use it

Only the login nodes install the screen. i.e. only login.storrs.hpc.uconn.edu.

How to use it

To start using screen

Simply run screen

[jth10001@login4 ~]$ screen

Congratulations, you are now inside of a window within screen. This functions just like a normal shell except for a few special characters.

Below is a complete guide of screen commands adapted from Carlos Tosta’s (jctosta) GitHub page.

Screen Quick Reference

Basic

Description	Command

Description	Command
Start a new session with session name	`screen -S <session_name>`
List running sessions / screens	`screen -ls`
Attach to a running session	`screen -x`
Attach to a running session with name	`screen -r <session_name>`
Detach a running session	`screen -d <session_name>`
Kill a running session	`screen -X -S [session # you want to kill] kill`
Accessing a screen that is already attached	`screen -r -d [session name]`

Escape Key

All screen commands are prefixed by an escape key, by default Ctrl-a (that's Control-a, sometimes written ^a). To send a literal Ctrl-a to the programs in screen, use Ctrl-a a. This is useful when when working with screen within screen. For example Ctrl-a a n will move screen to a new window on the screen within screen.

Getting Out

Description	Command

Description	Command
detach	`Ctrl-a d`
detach and logout (quick exit)	`Ctrl-a D D`
exit screen	`Ctrl-a :` quit or exit all of the programs in screen.
force-exit screen	`Ctrl-a C-\` (not recommended)

Help

Description	Command

Description	Command
See help	`Ctrl-a ?` (Lists keybindings)

Window Management

Description	Command

Description	Command
Create new window	`Ctrl-a c`
Change to last-visited active window	`Ctrl-a Ctrl-a` (commonly used to flip-flop between two windows)
Change to window by number	`Ctrl-a <number>` (only for windows 0 to 9)
Change to window by number or name	`Ctrl-a ' <number or title>`
Change to next window in list	`Ctrl-a n` or `Ctrl-a <space>`
Change to previous window in list	`Ctrl-a p` or `Ctrl-a <backspace>`
See window list	`Ctrl-a "` (allows you to select a window to change to)
Show window bar	`Ctrl-a w` (if you don't have window bar)
Kill current window	`Ctrl-a k` (not recommended)
Kill all windows	`Ctrl-a \` (not recommended)
Rename current window	`Ctrl-a A`

Split screen

Description	Command

Description	Command
Split display horizontally	`Ctrl-a S`
Split display vertically	`Ctrl-a
Jump to next display region	`Ctrl-a tab`
Remove current region	`Ctrl-a X`
Remove all regions but the current one	`Ctrl-a Q`

Misc

Description	Command

Description	Command
Redraw window	`Ctrl-a C-l`
Enter copy mode	`Ctrl-a [` or `Ctrl-a <esc>` (also used for viewing scrollback buffer)
Paste	`Ctrl-a ]`
Monitor window for activity	`Ctrl-a M`
Monitor window for silence	`Ctrl-a _`
Enter digraph (for producing non-ASCII characters)	`Ctrl-a Ctrl-v`
Lock (password protect) display	`Ctrl-a x`
Enter screen command	`Ctrl-a :`
Enable logging in the screen session	`Ctrl-a H`

Scrolling

Description	Command

Description	Command
Enter scrolling mode	`Ctrl-a esc`
Scroll Up	`Ctrl-u`
Scroll Down	`Ctrl-d`
Exit scrolling mode	`esc esc`

More Information

For more help visit GNU screen website. screen has functionality beyond just resuming and detaching from sessions.