One vital set of properties is the file's permissions. File permissions help prevent unwanted deletion and safeguard your data. In order to use Linux's file permissions, you need to understand Linux's categories of users and groups. You are asked to enter a login name and password when you first log into Linux. When we talk of a user , we refer to the account issuing commands to the operating system at the time and not to the actual person operating the computer.
Users belong to one or more groups.
Each user has a default group. The owner of the file. A user who creates a file automatically owns it. The group of a file. One group of users is given special access to a file.