D A T A W O K

Creation: August 28 2017
Modified: February 05 2022

Screen

One screen session can contain several screen windows. A window runs another program instance.

To start a new screen session

$ screen [command]

If an explicit command is not given then a shell is started.

A session has a unique identifier by default following the following pattern: pid.tty.host. You can give a more useful name (to reattach later) using the following command

$ screen -R name [command]

A window has a numeric identifier.

From a running session you can enter command mode holding the control key and pressing the 'a' character. Command mode allows you to enter speial characters to: create new windows, detach from screen session, etc.

`<C-a>` : enters command mode from a running `screen` session.

When in command mode, one command is one character. After the command is executed then the program goes back to normal mode.

Core commands

c : create and enter a new window
n : next window
p : prev window
N : print current window
d : detach

Split screen commands

S : split display horizontally
| : split display vertically
tab : jump to next display region
X : remove current region
Q : remove all regions bu the current one

Clipboard commands

[ : freely navigate buffer
] : paste

Use "space bar" to toggle selection to copy.

Core command line options

-list: List running screen sessions.
-r <session-id>: reattach to a screen session.
-R <session-id>: reattach to a screen session or create it first.
-RR <session-id>: like -R but resume the yungest if there are multiple possibilities (*).
-d <session-id>: detach a screen session
-D <session-id>: detach a screen session (logout if necessary)

(*): a session id is unique, however a partial session-id (without the pid prefix) can be specified. In this case there can be a conflict.

For example to detach a running screen session from the holding terminal and reattach it in the current one (given session-id: 123.pts-1.localhost)

$ screen -d -r pts-1

Run screen in a remote server

Screen can be extremely useful when is run above an SSH session because allows to:

Execute multiple programs in a single SSH session
Disconnect and reconnect later to an interactive program or to avoid waiting for a long run operation.

We use "weechat-curses" program as an example.

ssh <host> -t screen -D -RR mysessionid top

The command, after login, will

allocate a pseudo-tty (-t) and connects it to the screen session
look for a screen session named "weechat". It a session with that name exists, it will reattach to it (-D -RR).

Detach

Extra tip

To know if the current shell is running under screen or tmux check the STY and TMUX environment variables, respectively. If they are empty then you are not under a multiplexer.

Add the following to the .bashrc file to have the information always in the prompt.

if [ -n "$STY" ]; then
    export PS1="(s) $PS1";
fi
if [ -n "$TMUX" ]; then
    export PS1="(t) $PS1";
fi

The default statusbar may be little lacking. You may find this one more helpful:

~/.screenrc

hardstatus off
hardstatus alwayslastline
hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{= kw}%?%-Lw%?%{r}(%{W}%n*%f%t%?(%uu)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B} %m-%d %{W} %c %{g}]'

References

Linux screen tutorial @ rackaid

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