Screen sessions¶

GNU screen keeps terminal sessions running on the login node after you disconnect, and lets you open several shells ("windows", shown as tabs below) in one SSH connection. It is how you keep an interactive session or a VS Code tunnel alive. The login node has screen 4.6.

Start, leave and come back¶

Command	What it does
`screen -S work`	start a new session named `work`
`screen -ls`	list your sessions
`screen -r work`	reattach to the session `work`
`screen -d -r work`	reattach, detaching it first from wherever else it is still attached
`exit` in the last window	end the session

A detached session keeps running, including everything started in it, until you end it or the login node restarts.

Keys inside screen¶

Every screen command starts with the prefix key Ctrl+A. The command is two separate key presses, not one chord: press Ctrl+A, release both keys, then type the command character. For example, to open a new window, press Ctrl+A, let go, then type c.

Command characters are case-sensitive: a and A do different things.

Keys	What it does
`Ctrl`+`A` then `d`	detach: leave the session running and return to the login shell
`Ctrl`+`A` then `c`	create a new window
`Ctrl`+`A` then `n` / `p`	go to the next / previous window
`Ctrl`+`A` then `0` … `9`	go to window 0 to 9
`Ctrl`+`A` then `"`	list the windows and choose one
`Ctrl`+`A` then `A` (capital, `Shift`+`A`)	rename the current window
`Ctrl`+`A` then `[`	scroll back through the output (move with the arrow keys, leave with `Esc`)
`Ctrl`+`A` then `k`	close the current window (asks for confirmation)
`Ctrl`+`A` then `a`	send a literal `Ctrl`+`A` to the program, for example to jump to the start of the line in Bash
`Ctrl`+`A` then `?`	show all key bindings

The full list is in the GNU Screen manual, under default key bindings; see also the whole manual.

Show windows as tabs¶

By default screen shows no sign of which windows are open. With this ~/.screenrc on the login node, a status line at the bottom lists the windows like tabs, with the host name and the time:

# Use bash
shell /bin/bash

autodetach on

# Big scrollback
defscrollback 5000

# No annoying startup message
startup_message off

# Display the status line at the bottom
hardstatus on
hardstatus alwayslastline
hardstatus string "%{.kW}%-w%{.bW}%t [%n]%{-}%+w %=%{..G} %H %{..Y} %Y/%m/%d %c"

The current window is highlighted in the status line:

tmux¶

tmux (version 2.7) is installed too. It does the same job with a different prefix key (Ctrl+B) and commands; see its getting started guide.