Difference between revisions of "Screen terminal multiplexer"

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(Extra: Serial port using screen)
(Fixed some typos and added link to tmux documentation)
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{{pkg|screen}} is a good tool for 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 {{pkg|screen}} session). When you enter a {{pkg|screen}} session you will not notice too much.<BR>
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{{pkg|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 {{pkg|screen}} session you will not notice too much.<BR>
 
To know if you are inside a {{pkg|screen}} session, use the notes in '[[#Get_help|get help]]' section mentioned below.
 
To know if you are inside a {{pkg|screen}} session, use the notes in '[[#Get_help|get help]]' section mentioned below.
  
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or
 
or
 
{{cmd|screen -x pts-3}}
 
{{cmd|screen -x pts-3}}
{{tip|If you see <code>Attaching from inside of screen?</code>, you are allready inside a screen session.}}
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{{tip|If you see <code>Attaching from inside of screen?</code>, you are already inside a screen session.}}
  
 
== Controlling a screen session ==
 
== Controlling a screen session ==
While inside a {{pkg|screen}} session, you can controll it using keyboard shortcuts. We will only describe some of those alternatives.
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While inside a {{pkg|screen}} session, you can control it using keyboard shortcuts. We will only describe some of those alternatives.
  
 
{{tip|To enter a keyboard shortcut that controls the current {{pkg|screen}} session, you should click {{key|A}} while holding down {{key|CTRL}}<br>In the below examples this procedure is described as <code>^A</code>}}
 
{{tip|To enter a keyboard shortcut that controls the current {{pkg|screen}} session, you should click {{key|A}} while holding down {{key|CTRL}}<br>In the below examples this procedure is described as <code>^A</code>}}
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Sometimes it's useful to just detach from a session without killing it.<br>
 
Sometimes it's useful to just detach from a session without killing it.<br>
 
{{cmd|^A d}}
 
{{cmd|^A d}}
{{tip|Try starting <code>ping 127.0.0.1</code> while inside a screen session and then detatch from the session.<br>After some while re-connect to the session using <code>screen -x</code>.<br>Note that the "seq" value indikates that ping had continued running while you where detatched from the session.}}
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{{tip|Try starting <code>ping 127.0.0.1</code> while inside a screen session and then detach from the session.<br>After some while re-connect to the session using <code>screen -x</code>.<br>Note that the "seq" value indicates that ping had continued running while you where detached from the session.}}
  
 
=== Close or kill a session ===
 
=== Close or kill a session ===
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Remove this part from above configuration to force SSH sessions into a screen session.<BR>
 
Remove this part from above configuration to force SSH sessions into a screen session.<BR>
 
{{Note|Console users will also be forced into a screen session when folowing these instructions}}
 
{{Note|Console users will also be forced into a screen session when folowing these instructions}}
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= Other terminal multiplexers =
 +
A similar tool is {{pkg|tmux}} which is documented [[Tmux_terminal_multiplexer|here]].
  
 
[[Category:Shell]]
 
[[Category:Shell]]

Revision as of 14:11, 24 October 2012

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

Tip: If you see 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.

Tip: To enter a keyboard shortcut that controls the current screen session, you should click A while holding down CTRL
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

Tip: Try starting 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' you 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 bash 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.

Note: Console users will also be forced into a screen session when folowing these instructions

Other terminal multiplexers

A similar tool is tmux which is documented here.