Setting Ownership
Linux’s security model is based on that of Unix, which was designed as a multiuser OS. This security model therefore assumes the presence of multiple users on the computer, and it provides the means to associate individual files with the users who create them—that is, files have owners. You should thoroughly understand this concept, and with that understanding, you can change a file’s ownership, using either a GUI file manager or a text-mode shell.
Ownership also applies to running programs (or processes). Most programs that you run are tied to the account that you used to launch them. This identity, in conjunction with the file’s ownership and permissions, determines whether a program may modify a file.
Understanding Ownership
Chapter 12, ...