I tried using DISPLAY=:0 import -window root "$HOME/Pictures/screenshot.png" (import is part of the ImageMagick suite), but that just displays a black screen.
I want to do this as I wanted to automate opening an app and taking screenshots of it in different languages, and to change languages, I need to restart lightdm. therefore, run on a tty so your script continues running...
In addition to the existing answers, to display the screenshot in ASCII in the terminal:
xwd -root -display :0 | convert - jpg:- | jp2a - --colors(Requires x11-apps for xwd, imagemagick for convert and jp2a.)
xwd format from magic numbers, so it's better to specify the input format explicitly: xwd -root -display :0 | convert xwd:- jpg:- | jp2a - --colors
xwd -name "$win_name" | convert xwd:- /tmp/"$win_name".png, where win_name=$(xwininfo -tree -root | grep 'The Window Name Im Looking For' | awk -F\" '{print $2}')
Here is solution using xwd, which is is available in almost all Xorg installations:
xwd -root -out screenshot.xwd
The screenshot.xwd file can be opened with GIMP:
For more info see http://www.x.org/wiki/UserDocumentation/GettingStarted/.
Here's what worked for me.
chvt 7
DISPLAY=:0 import -window root "$HOME/Pictures/screenshot.png
chvt 1
Try using shutter
DISPLAY=:0 shutter -f -e -n -o "$HOME/Pictures/screenshot.png"
Import won't work, because the root window is not in use. Compositing "bypasses" it (each window is rendered in its own buffer then multiplexed to the display, instead of the old way, where they were all rendered on the "root" window).
In addition you need to make sure the VTY is active before you take the screenshot. So for example,
#!/bin/bash
X :1 &
export DISPLAY=:1
sleep 10 # give time for X to start
gedit &
sleep 10 # give time for app to do something
chvt 8 # ensure the X display is active
shutter -f -e -n -o "$HOME/Pictures/screenshot.png" # screenshot
killall xorg # terminate X
Sitting on the same computer and doing it from a different virtual terminal than the X server is running does not work.
It is explained there: http://www.karlrunge.com/x11vnc/faq.html#faq-linuxvc. Quote:
Q-108: I use Linux Virtual Terminals (VT's) to implement 'Fast User Switching' between users' sessions (e.g. Betty is on Ctrl-Alt-F7, Bobby is on Ctrl-Alt-F8, and Sid is on Ctrl-Alt-F1: they use those keystrokes to switch between their sessions.) How come the view in a VNC viewer connecting to x11vnc is either completely black, doesn't update, or pixels messed up unless the X session x11vnc is attached to is in the active VT?
This seems to have to do with how applications (the X server processes in this case) must "play nicely" if they are not on the active VT (sometimes called VC for virtual console.) That is, they should not read from the keyboard or mouse or manage the video display unless they have the active VT. Given that it appears the XGetImage() call must ultimately retrieve the framebuffer data from the video hardware itself, it would make sense x11vnc's polling wouldn't work unless the X session had active control of the VT.
There does not seem to be an easy way to work around this. Even xwd(1) doesn't work in this case (try it.) Something would need to be done at a lower level, say in the XFree86/Xorg X server. Also, using the Shadow Framebuffer (a copy of the video framebuffer is kept in main memory) does not appear to fix the problem (last checked 2007.)
If no one is sitting at the workstation and you just want to remotely switch the VT over to the one associated with your X session (so x11vnc can poll it correctly), one can use the chvt(1) command, e.g. "chvt 7" for VT #7.
