Difference between revisions of "Screen terminal multiplexer"

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(delete Category:Networking)
(Restructuring a bit. Adding some notes and examples that indicates how screen can be used)
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'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 'screen' session). When you enter a 'screen' session you will not notice too much.<BR>
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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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To know if you are inside a 'screen' session, use the notes in '[[#Get_help|get help]]' section mentioned below.
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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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= Install =
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= General =
 +
== Install ==
 +
In order to use {{pkg|screen}} you will have to install it:
 
{{cmd|apk add screen}}
 
{{cmd|apk add screen}}
  
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= Use screen =
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= Usage =
 +
 
 
== Start a new session ==
 
== Start a new session ==
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To enter a {{pkg|screen}} session you just enter:
 
{{cmd|screen}}
 
{{cmd|screen}}
  
 
== List existing sessions ==
 
== List existing sessions ==
 +
When you have started some session(s) you can list them:
 
{{cmd|screen -list}}
 
{{cmd|screen -list}}
 
You might get a list that looks like this:
 
You might get a list that looks like this:
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== Attach to a existing session ==
 
== Attach to a existing session ==
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Lets say you want to attach to a existing session (e.g. the above "11131.pts-3.mhlab01" session).
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Lets say you want to attach to a existing session (e.g. the above <code>11131.pts-3.mhlab01</code> session).
 
{{cmd|screen -x 11131}}
 
{{cmd|screen -x 11131}}
 
or
 
or
 
{{cmd|screen -x pts-3}}
 
{{cmd|screen -x pts-3}}
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{{tip|If you see <code>Attaching from inside of screen?</code>, you are allready inside a screen session.}}
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 +
== Controlling a screen session ==
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While inside a {{pkg|screen}} session, you can controll 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>}}
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=== Get help ===
 +
One of the most useful commands is the one that gives you 'help'.<br>
 +
While in your {{pkg|screen}} session, click:
 +
{{cmd|^A ?}}
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''(Do not press/hold {{key|CTRL}} when clicking {{key|?}})''
 +
 +
=== Detach from a session ===
 +
Sometimes it's useful to just detach from a session without killing it.<br>
 +
{{cmd|^A d}}
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{{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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== Close or kill a session ==
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=== Close or kill a session ===
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When you are inside a 'screen' session you can 'kill' it by using:
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To 'kill' a session:
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{{cmd|CTRL+A k}}
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{{cmd|^A k}}
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or you might just type:
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Confirm by clicking {{key|y}} when prompted.
 +
 
 +
You can also 'kill' you session by entering:
 
{{cmd|exit}}
 
{{cmd|exit}}
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== Get help ==
 
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'screen' has various options/commands.<BR>
 
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When your inside a 'screen' session you can get help and see what options you have by using:
 
−
{{cmd|CTRL+a ?}}
 
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''(Do not press/hold 'CTRL' when entering ''''?'''')''
 
  
 
= Extra =
 
= Extra =
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In some cases you might want to force only console users into a screen session.<BR>
 
In some cases you might want to force only console users into a screen session.<BR>
 
Note that the this configuration will not force SSH-users into a screen.<BR>
 
Note that the this configuration will not force SSH-users into a screen.<BR>
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Edit `/etc/profile` and add the following code to it:
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Edit {{path|/etc/profile}} and add the following code to it:
 
<pre>
 
<pre>
 
if [ -n "$PS1" ] && [ -z "$STARTED_SCREEN" ] && [ -z "$SSH_TTY" ]; then
 
if [ -n "$PS1" ] && [ -z "$STARTED_SCREEN" ] && [ -z "$SSH_TTY" ]; then

Revision as of 10:05, 24 October 2012

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 screen 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.

General

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 allready inside a screen session.

Controlling a screen session

While inside a screen session, you can controll 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 detatch from the session.
After some while re-connect to the session using screen -x.
Note that the "seq" value indikates that ping had continued running while you where detatched 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

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
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