I have run out of space on my boot drive, so I decided to remove old kernels. I found this page which describes exactly what I should do: Lubuntu Documentation: Remove Old Kernels.
I have deleted the oldest kernel manually and now it is okay, but I don’t understand one thing: at the end of the article there is some code that can delete all old kernel versions, but it is marked as for advanced users only.
I don’t really understand what the danger is here. It sounds silly, but they seem to say that there might be more than one kernel used by a specific machine at the same time.
Is it possible that different applications on my Ubuntu machine can use different kernels simultaneously? Why is deleting all old kernels automatically considered to be dangerous?