How can I take a screenshot of the login screen?

Question

How can I take a screenshot of the login screen?

I do not want to recreate my Ubuntu installation in a virtual machine.

Answer 1

This blog might be helpful: http://ptspts.blogspot.com/2010/02/how-to-create-screen-shot-of-gdm-login.html

Install ImageMagick for the image file format conversion below:

$ sudo apt-get install imagemagick

Create a helper script:

$ echo 'DISPLAY=:0 XAUTHORITY=/var/lib/gdm/:0.Xauth xwd -root' >/tmp/shot.sh

Make sure your login screen is active (log out or reboot the machine, and wait until you see the login screen). Log in in text mode (by pressing Ctrl-Alt-F1), or using SSH. Create the screen shot by running

$ sudo bash /tmp/shot.sh >/tmp/shot.xwd

You can log in now (by pressing Ctrl-AltF7 first to get back to the GDM login screen). Convert the screen shot to JPEG and/or PNG:

$ convert -quality 50 /tmp/shot.xwd /tmp/shot.jpg
$ convert /tmp/shot.xwd /tmp/shot.png

View the screen shot in your favourite image viewer.

Answer 2

For 11.10 and Lightdm and later

You can try running unity-greeter --test-mode in a terminal. It displays the login screen within the session. You can then take a screenshot of the login screen like you normally do with any other application.

Answer 3

Just wanted to note that I had a bunch of problems doing this on Ubuntu 10.04 LTS with this - here's my solution:

I'm on machine A, and I log on to machine B via ssh:

myusername@pcA:~$ ssh pcB
myusername@pcB's password: 
Linux pcB 2.6.32-44-generic #98-Ubuntu SMP Mon Sep 24 17:32:45 UTC 2012 i686 GNU/Linux
Ubuntu 10.04.4 LTS

Welcome to Ubuntu!
 * Documentation:  https://help.ubuntu.com/

myusername@pcB:~$ 

Then, I proceed with several attempts to grab screenshot, which all failed. The problem can be reduced down to xwininfo being unable to probe for the window state:

myusername@pcB:~$  xwininfo
xwininfo:  unable to open display ''

myusername@pcB:~$ sudo xwininfo
[sudo] password for myusername: 
xwininfo:  unable to open display ''

myusername@pcB:~$ DISPLAY=:0.0 xwininfo
No protocol specified
xwininfo:  unable to open display ':0.0'

myusername@pcB:~$ DISPLAY=:0 xwininfo
No protocol specified
xwininfo:  unable to open display ':0'

Well, it turns out that for some reason, the correct invocation for targeting X-windows via ssh is DISPLAY=:0.0 sudo xwininfo ... - that is, the DISPLAY=:0.0 environment variable goes first; the sudo goes second - and then the corresponding X command:

myusername@pcB:~$ DISPLAY=:0 sudo xwininfo

xwininfo: Please select the window about which you
          would like information by clicking the
          mouse in that window.

myusername@pcB:~$ DISPLAY=:0.0 sudo xwininfo -root

xwininfo: Window id: 0x109 (the root window) (has no name)

  Absolute upper-left X:  0
  Absolute upper-left Y:  0
  Relative upper-left X:  0
  Relative upper-left Y:  0
  Width: 1366
  Height: 768
  Depth: 24
  Visual: 0x21
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x20 (installed)
  Bit Gravity State: ForgetGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: no
  Map State: IsViewable
  Override Redirect State: no
  Corners:  +0+0  -0+0  -0-0  +0-0
  -geometry 1366x768+0+0

Now that we know xwininfo can probe the state, there is also no problem with capturing the screenshot via xwd:

myusername@pcB:~$ DISPLAY=:0.0 sudo xwd -root > /tmp/shot.xwd

Hope this helps someone,
Cheers!