Understanding file and directory permissions is critical for Linux security because Linux is a multiuser environment, and permissions are designed to protect your work from others. To understand permissions, you first need to know the types of permissions available in Linux and how they differ when applied to files versus to directories.
Once you understand the different permissions, you need to know how to set them. Linux provides two methods: the symbolic method and the octal (or numeric) method.
You also learn about special permissions in this chapter, including SUID, SGID, and sticky bit. These permissions provide special access to files and directories and are typically managed by the system administrator.