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Using screen for support and/or surveillance

Often support customers want to see what you do on their databases. For this screen is the ideal tool.

Screen commands typically look like this:

screen> Ctrl+a ?

This means press Ctrl+a, release Ctrl+a, press ? and NOT press Ctrl+a+? together. Often you can find Ctrl+A which is wrong. It is a lower case a!

Start first screen

Start and leave a screen:

shell> screen
screen> exit

or k for kill

screen> Ctrl+a k

Comment: Does not work if done with sudo, typically used with ssh.

A screen can be named as follows:

shell> screen -S support

List available screens

You can find your available screens like this:

user1_shell> screen -ls
There are screens on:
        11212.support   (05/21/2012 03:10:23 PM)        (Attached)
        5358.pts-4.master       (05/21/2012 03:08:08 PM)        (Attached)
2 Sockets in /var/run/screen/S-user1.

User2 cannot see those:

user2_shell> screen -ls
No Sockets found in /var/run/screen/S-user2.

but user2 can see all screens like this:

user2_shell> ps -ef | grep screen | grep -v grep
user1     5357 24626  0 15:08 pts/4    00:00:00 screen
user1    11211 11105  0 15:10 pts/7    00:00:00 screen -S support

Screen help

You get help about screen:

shell> screen --help
shell> man screen
screen> Ctrl+a ?

Create a new window in screen

To create several windows in screen use c for create:

screen> Ctrl+a c

List all available windows:

screen> Ctrl+a "

Scroll to previous/next or nth window:

screen> Ctrl+a n
screen> Ctrl+a p
screen> Ctrl+a 0
screen> Ctrl+a 1

Detach and re-attach to a screen

Detach from screen:

screen> Ctrl+a d

List available screens and attach to a screen:

shell> screen -ls
shell> screen -r 4670.pts-4.master

Logging screen sessions

Ctrl+a h

Configure screen

#
# ~/.screenrc
#

# Don't show the slash screen
startup_message off

# Use visual bell
vbell on

# Set a big scrolling buffer
defscrollback 5000

# Support UTF-8
defutf8 on

Assign meaningful names to a screen window

screen> Ctrl+a A
Server1

Scroll in screen

Start scroll mode:

screen> Ctrl+a ESC

Then scroll up and down. To get back in normal screen mode press ESC.

Lock/unlock screen

screen> Ctrl+a s
screen> Ctrl+a q

Sharing screen with same shell user

user1_shell> screen -S support

user1_shell> screen -r support
There is a screen on:
        17831.support   (05/21/2012 03:36:29 PM)        (Attached)
There is no screen to be resumed matching support.
user1_shell> screen -r support -x

Caution: If one of both windows does an exit, both windows will close!

If you get the following error message: Cannot open your terminal '/dev/pts/2' - please check. the following can help (as the owner of the device):

chmod 666 /dev/pts/2

Sharing screen with other shell user

You have to prepare as user root:

chmod u+s /usr/bin/screen
chmod 755 /var/run/screen

Then as user1:

user1_shell> screen -S support
user1_screen> Ctrl+a :multiuser on
user1_screen> Ctrl+a :acladd user2

and as user2:

shell_user2> screen -x user1/support

Literature

  1. Screen - howto
  2. LinuxQuestions.org > Linux Wiki > Screen
  3. Screen User's Manual