LinuxPowered.com: Linux file permissions & ownershipDec 19, 1999, 18:18 (0 Talkback[s])
(Other stories by Ofir Arkin)
"In a multi user system you need a way to protect each user from another. One of the reasons is that a user can abuse the system for his needs, or be able to read/modify/kill another user work. Even if your using your linux box in a single-user mode you need to protect your self from making deadly mistakes that can kill your system."
"On a plain file thier are three permission attributes: read (r), write (w), execute (x). Read permission let you read the data from a file. Write permission let you write new data to a file. Execute permission let you use the file as a program or a shell sctipt."
"Same permission apply fot directories but they have a different meaning. If a directory has read permission you can see what files are in the directory, write permission to a directory means you can add, remove or rename files in the directory. Execute permission (also called the "search bit") allow you to use the directory name when accessing files inside that directory."