How is the permission system and access control to files implemented in the Linux operating system?

In Linux, the permission system for files is based on three types of access rights: read (r), write (w), and execute (x). These rights are set for three categories of users:

• File owner
• Group to which the file belongs
• All other users

Each right is represented by a bit, and the combination of these bits determines what the user can do with the file.

For example, the permissions rwxr-xr-- mean:

• Owner: read, write, execute
• Group: read, execute
• Others: read only

To manage permissions, commands like chmod (change permissions), chown (change owner), and chgrp (change group) are used.

Besides basic permissions, Linux also has advanced access control mechanisms such as ACLs (Access Control Lists), which allow setting more fine-grained permissions for individual users or groups.