Every file and directory in a Linux system is governed by a set of security-related properties. These properties govern the life of the file or directory in two ways:
Each file or directory must be owned by someone: In Linux, there is no such thing as a file or directory without an owner.
Each file or directory is associated with a list of the operations that can be performed on it, both by the owners and at times by other users as well. This list is known as the file's permissions and it is generally represented in a particular visual format that we discuss in a moment.
Both ownership and permissions are assigned from default values when a file or directory is created; file or directory owners can then change this information ...