I was wondering how they did come up with the way of setting permissions using the linux program chmod by just using numbers. For example: Code (Text): 1 is for execute 2 is for write 4 is for read Any sum of those give a unique permission to a file: 2+4=6 Lets you write and read it. 1+4=5 Let's you execute and read it. So is there an algorithm behind this? Say for example that I have 5 different items and I want to be able to pass a single number and the other person to understand which combination of items I made.