chmod, chgrp, and chown
A sophisticated system of users and permissions precisely controls who has access to what on Linux. At the command line, you can define ownership with the chmod, chgrp, and chown tools.
Granular access privileges for files and directories are what make Linux a safe operating system. A precise definition of who is permitted to read, modify data, or execute specific programs provides excellent protection against any prying eyes and intentional misconfiguration. The administrator, root, is subject to no restrictions, and this includes assigning read, write, and execute permissions to other users throughout the system. If you are the owner of a file or directory, you can grant access to these resources to other accounts. If you are also a member of a specific group, you can modify the group ownership of files and folders for more granular permission assignments to files.