If I run this command in Ubuntu
sudo cat /proc/sys/kernel/random/entropy_avail
it returns a number that indicates how much "entropy" is available to the kernel, but that's about all I know. What unit is this entropy measured in? What is it used for? I've been told it's "bad" if that number is "low". How low is "low" and what "bad" things will happen if it is? What's a good range for it to be at? How is it determined?