“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.”