how to install and configure screen on centos 7

How To Install and Configure Screen on CentOS 7

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Table of Contents

Overview ....................................................................................................................................................... 1

Applies To ...................................................................................................................................................... 1

Pre-Requisites ............................................................................................................................................... 1

Install Package – Screen ................................................................................................................................ 1

Verify – Package Installation ..................................................................................................................... 2

Launch – New Screen Session ................................................................................................................... 2

List – Screen Session ................................................................................................................................. 3

Attach – Screen Session ............................................................................................................................ 3

Detach – Screen Session ........................................................................................................................... 4

Lock – Screen Session ............................................................................................................................... 4

Create – New Screen ................................................................................................................................. 4

Switch – Next Screen Session................................................................................................................ 5

Switch – Previous Screen Session ......................................................................................................... 5

Switch – List Screen Session .................................................................................................................. 5

Stop – Screen Session ............................................................................................................................... 6

Wipe – Screen Session .............................................................................................................................. 6

Scroll back – Screen Session...................................................................................................................... 7

Split – Screen Session ................................................................................................................................ 7

Split – Screen Session – Start Session ................................................................................................... 8

Split – Screen Session – Switch Session ................................................................................................ 8

Split – Screen Session – Exit Session ..................................................................................................... 9

Share – Screen Session – Other Users ...................................................................................................... 9

SUID Permissions – Modify ................................................................................................................... 9

SUID Permission – Error ...................................................................................................................... 10

Start – Screen Session – Name............................................................................................................ 10

Access – Screen Session – Name ......................................................................................................... 11


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Overview

GNU Screen is a terminal multiplexer, a software application that can be used to multiplex several virtual consoles, allowing a user to access multiple separate login sessions inside a single terminal window, or detach and reattach sessions from a terminal.

It is useful for dealing with multiple programs from a command line interface, and for separating programs from the session of the Unix shell that started the program, particularly so a remote process continues running even when the user is disconnected.

In this guide we will install screen, configure and check different options to utilize it.

Applies To

CentOS 7, tested on CentOS Linux release 7.3.1611 (Core)

Pre-Requisites

superuser access for installation.

Install Package – Screen

In this section we will go over the steps for installation of screen.

To install screen package, run the command;

yum install screen -y


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Verify – Package Installation

To check the package is installed, run the command;

yum list installed | grep screen or

rpm -qai screen | grep -E "Name|\ Install Date"

Launch – New Screen Session

To initialize / start a new screen session, run the command;

screen

A new “Screen 0” has been created.


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List – Screen Session

To list created screens and that are available to connect, run the command;

screen -ls

Attach – Screen Session

To list screen sessions available / started session, screen ID is associated with the process ID of the session, run the command;

screen -r 14733


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Detach – Screen Session

After starting / connecting, to disconnect and keep the processes running without being terminated, you need to detach the screen session, to disconnect an active session run the command;

Ctrl + A and D or Ctrl + A and Ctrl + D

Lock – Screen Session

At times locking screen would be required typically when you intended to step away from the system, to lock screen run the command; password of the login user has to be entered to unlock the screen session.

Ctrl + X

Create – New Screen

To will launch a new screen session within existing screen session, we can create 10 screen sessions, these screen session windows will be will be titled from screen:[0 to 10], run the command;

screen


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Switch – Next Screen Session

To navigate to next screen, run the command;

Ctrl + A and n

Switch – Previous Screen Session

To navigate to next screen, run the command;

Ctrl + A and p

Switch – List Screen Session

To list and switch to selected screen, run the command;

Ctrl + A and "


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Stop – Screen Session

To stop / kill a screen session, run the command;

Ctrl + A and k

Or Ctrl + D

Wipe – Screen Session

In some scenarios, screen session is abruptly killed or process ID of “SCREEN” is killed in such cases screen session ID is in a defunct or dead state or it is also considered as unreachable session, you have to clean the screen by running the command;

screen -ls

screen -wipe


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Scroll back – Screen Session

By default screen scroll back buffer is configured to display 100 lines; to increase the scroll back buffer, this option can be tweaked by running the command;

screen -h 200

Split – Screen Session

At times you want to split screen to work on some task and would like to see the progress of the task simultaneously, for this you can utilize split screen sessions. Screen splits can be done horizontally or vertically. In this section we check different options.

This option is useful to check real time logs in one window and other window you are performing some task that would impact the log generated.

Ctrl A + S


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Split – Screen Session – Start Session

After Splitting the screen, to utilize the split screen you need to create a new screen session, shell prompt will be enabled / created to work in the split screen, run the command;

Ctrl A + C

Split – Screen Session – Switch Session

After creating the screen if you want to switch between screen sessions, run the command;

Ctrl A + <TAB Key>

Note: To split vertically, run the command “Ctrl A + |”


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Split – Screen Session – Exit Session

If you intended to close the split session, run the command;

Ctrl A + Q

Share – Screen Session – Other Users

At times you intended to share the screens with others on the servers, in this section we will configure to be able to share the screen sessions with other users.

SUID Permissions – Modify

First step is to configure SUID permission, in order to share the screen sessions between different users on the server, permissions have to be tweaked. Again this security poses a security risk, though this configuration is a necessity to ensure that users have access to see screen sessions.

chmod +s /usr/bin/screen

chmod 755 /var/run/screen


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SUID Permission – Error

If the SUID permissions has not been configured and try to share the session, error message will be displayed as below;

“Must run suid root for multiuser support”

Start – Screen Session – Name

Next step is to start the screen session associated with a name which will help us in easier identification, to start a screen session associated with a name to it, run the command;

screen -S TestingSharingSession


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Access – Screen Session – Name

Now that we have configured and started the session, when the other user wants to access, from his login session run the command;

screen -x root/TestingSharingSession

how to install and configure screen on centos 7

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