Setting Ownership and Permissions
Christine Bresnahan, Richard Blum · 2012
This chapter describes how to manage file permissions and ownership. The security model for Linux 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 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 knowledge, you can help protect your files, using either a GUI file manager or a text-mode shell command. Ownership also applies to running programs. Most programs you run are tied to the account you used to launch them. This identity, in conjunction with the file's ownership and permissions, determines whether a program may modify a file. File ownership is meaningless without some way to specify what particular users can do with their own or other users' files. That's where permissions enter the picture. Linux's permission structure is modeled after that of Unix, and it requires a bit of explanation before you tackle the issue. After you understand the basics, you can begin modifying permissions, using either a GUI file manager or a text-mode shell. You can also set default permissions for new files you create.