Screen terminal multiplexer
screen is a terminal multiplexer. It's a good tool for e.g. remote support. It can also be used to start a command you want to keep running after you close your console session (you can later on attach to your running session). When you enter a screen session you will not notice too much.
To know if you are inside a screen session, use the notes in 'get help' section mentioned below.
Install
In order to use screen you will have to install it:
apk add screen
Usage
Start a new session
To enter a screen session you just enter:
screen
List existing sessions
When you have started some session(s) you can list them:
screen -list
You might get a list that looks like this:
There are screens on: 11151.pts-1.mhlab01 (Attached) 11131.pts-3.mhlab01 (Attached) 2 Sockets in /var/run/screen/S-root.
Attach to a existing session
Lets say you want to attach to a existing session (e.g. the above 11131.pts-3.mhlab01
session).
screen -x 11131
or
screen -x pts-3
Attaching from inside of screen?
, you are already inside a screen session.Controlling a screen session
While inside a screen session, you can control it using keyboard shortcuts. We will only describe some of those alternatives.
In the below examples this procedure is described as
^A
Get help
One of the most useful commands is the one that gives you 'help'.
While in your screen session, click:
^A ?
(Do not press/hold CTRL when clicking ?)
Detach from a session
Sometimes it's useful to just detach from a session without killing it.
^A d
ping 127.0.0.1
while inside a screen session and then detach from the session.After some while re-connect to the session using
screen -x
.Note that the "seq" value indicates that ping had continued running while you where detached from the session.
Close or kill a session
To 'kill' a session:
^A k
Confirm by clicking y when prompted.
You can also 'kill' your session by entering:
exit
Extra
Connect to serial console
screen is a good tool when you need to connect to a serial console (e.g. if you want to configure a switch using it's serial port). Connecting to a serial console could look like this:
screen /dev/ttyS0 9600
Force console users into a screen session
In some cases you might want to force only console users into a screen session.
Note that the this configuration will not force SSH-users into a screen.
Edit /etc/profile and add the following code to it:
if [ -n "$PS1" ] && [ -z "$STARTED_SCREEN" ] && [ -z "$SSH_TTY" ]; then STARTED_SCREEN=1 ; export STARTED_SCREEN screen -RR && exit 0 echo "Screen failed! continuing with normal startup" fi
Force console and SSH users into a screen session
The above example holds the if-statement:
&& [ -z "$SSH_TTY" ]
Remove this part from above configuration to force SSH sessions into a screen session.
Other terminal multiplexers
A similar tool is tmux which is documented here.
Configuring .screenrc (example)
#hardstatus off hardstatus alwayslastline '%{= kG}[ %{y}%H%? %1`%?%{g} ][%= %{= kw}%-w%{+b yk} %n*%t%?(%u)%? %{-}%+w %=%{g}][ %{y}%l %{g}][%{W}%c:%s %{g}]' msgwait 1 vbell off # Huge scrollback buffer defscrollback 5000 # No welcome message startup_message off # Clear the screen after closing some programs altscreen on # Get rid of the vertical bars rendition so =00 caption string "%{03} " # 256 colors term screen-256color terminfo rxvt-unicode 'Co#256:AB=\E[48;5;%dm:AF=\E[38;5;%dm' termcapinfo xterm* ti@:te@ attrcolor b ".I" # UTF-8 #defutf8 on #utf8 on # Default Windows # Switch windows with F3 (prev) and F4 (next) bindkey "^[OR" prev bindkey "^[OS" next # Get rid of silly xoff stuff bind s split bind c screen 1 bind ^c screen 1 bind 0 select 10 screen 1 # remove some stupid / dangerous key bindings bind k bind ^k bind . bind ^\ bind \\ bind ^h bind h hardcopy bind 'K' kill bind '}' history bind L screen -t dmesg 10 watch "dmesg | tail -n $((LINES-42))" bind T screen -t htop 11 htop bind A screen -t atop 12 atop bind N screen -t nethogs 15 nethogs bind V screen -t vnstat 16 vnstat bind S screen -t ss 17 ss -s
Where to find more examples
- Archlinux forums (https://bbs.archlinux.org/viewtopic.php?id=55618) - GithubGist (https://gist.github.com/search?utf8=%E2%9C%93&q=screenrc) - Github (https://github.com/search?utf8=%E2%9C%93&q=screenrc)