HOWTO take a screenshot
Taking a screenshot of your application or desktop in GNU/Linux can be done with almost countless ways. Here are some.
The Print Screen Button
While somewhat obvious that pressing this key would let you take a screenshot in XFCE4 and KDE Plasma it's actually something few people know. Now you know: Pressing this button opens a small program which allows you to take a full-screen screenshot and either save it or open it directly in a program like Krita or GIMP.
Using a graphical program
You can take a screenshot with GIMP by going to the main menu
Using the command-line in a terminal
If you have
imagemagick installed, and you probably do (click here to install on Ubuntu if you don't) then you can use it's
import (manual page) program to take a snapshot of your dekstop. Use it like this:
import -window root screenshot.png
You can also use xv.
<!/--- add manual page link later /--->
xv is in principle for interactive image display but it's secretly got quite a few image conversion and manipulation features listed in
xv --help (not in the manual page for some reason). You can use it to take a screenshot with:
xv -grabdelay 2 myimage.jpg
then there is scrot. It is a standalone program you probably don't have pre-installed but it's easy to install since it's in all distributions repositories. It's been around since 2000. One interesting advantage it has is that you can save filenames using patters,
scrot '%Y-%m-%d_$wx$h.png' will create a screenshot file named something like 2019-10-30_2560x1024.png which makes it easy to know time and resolution later on.
Then there is
xwd. It's been around since forever and comes with X so probably have it installed. You probably don't want to use it but if you do you can use it like this:
xwd -root -out test.xwd
Screenshots created by xwd has to be saved as .xwd files. GIMP supports those and so does some obscure thing called xwud but that's about it.
Taking a screenshot of a framebuffer terminal
The best option for taking a screenshot of your framebuffer terminal at VT1 appears to be
fbgrab. Using it once you have it is strait forward,
however getting it is not. Distributions do not come with it and most don't have it in their repositories. Thus, you need to get it from it's homepage at https://www.fbgrab.monells.se/ and compile it yourself.