Historically, one of the great advantages unix systems had over their competitors was the notion of permissions: being able to control exactly what people can do with your files. If you want to stop other people from copying that final year project you've been working on for months, permissions is the way to do it; similarly, if you want to share documents or files with other users, understanding permissions is very important.

Understanding permissions is important for:

• Keeping files private from other users
• Sharing files with other users
• Dynamic websites