Description

Screen allows you to run scripts or commands in their own virtual window within the terminal, essentially allowing you to have a terminal multi-tasking environment where you can switch between your windows or another users at will. This howto will give you the basics of screen plus some other useful features that may help you in your daily administration tasks. This howto is intended to get you up and running with basic screen functionality within just a few minutes. Please read the manpage for a far more in-depth description of features and options.

Requirements

These are requirements for successfully completing this document.

1. Root or appropriate sudo access to the system.

Doing the Work

Basic description of what will be done and what is expected.

1. Install screen if it’s not already installed.

yum install screen

2. Setup screen for multi-user mode.

Multi-user mode is helpful for sharing a terminal and showing something in real-time because multi-user mode allows 1 or more people observe another performing commands or other system maintenance, or it could allow more than one user access to the status of scripts or custom commands running in separate screens.

Further reading on Screen multi-user mode and available commands.

setuid the screen binary.
chmod u+s /usr/bin/screen

Edit /etc/screenrc and add this at the top:

###Multi-user Mode### multiuser on acladd your_username,username,username aclchg your_username,username,username acldel your_username,username,username ###End Multi-user Mode###

1 2 3 4 5 6

###Multi-user Mode### multiuser on acladd your_username,username,username aclchg your_username,username,username acldel your_username,username,username ###End Multi-user Mode###

Useful screen commands

• List a particular users screen sessions.

screen -list username/ (the forward slash is important)

• List your own active screen sessions.

screen -ls

• Re-attach to a specific users screen and session.

screen -x username/shared-session

• Start a screen session and give it a unique name.

screen -S unique_name

• Detach from a running screen session leaving it running in the background.

Hit the key combination:
Control + A/a + D/d (not case sensitive)

• Re-attach to a specific screen you’ve named.

screen -R unique_name

• Power detach a screen that you are logged into from another location.

This is helpful if you’ve been accidentally disconnected from ssh while in a remote screen session and it’s still attached.
screen -D unique_name

Troubleshooting & Testing

Explanation troubleshooting basics and expectations.

1. Read the manpage:

man screen

2. Can’t find screen or it can’t be found via Yum?

Make sure you’re running authentic Centos and not using a custom 3rd party VPS container, Cpanel, or other shared hosting discount server.

The output of this command should tell you what you have:
uname -a; cat /etc/redhat-release

Output:


Linux example.com 2.6.32-573.12.1.el6.x86_64 #1 SMP Tue Dec 15 21:19:08 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux CentOS release 6.7 (Final)

1 2	Linux example.com 2.6.32-573.12.1.el6.x86_64 #1 SMP Tue Dec 15 21:19:08 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux CentOS release 6.7 (Final)