Unix by Nick Gomez, Chris Rees, Brian Hernandez, Hector Rodriguez

Why Special Files?

• Provides little distinction between files and devices
• Programs expecting files to read/write to can also accept devices without needing to differentiate the two
• Devices are subject to the same protection mechanics that files have

Removable File System

Another unique feature of the UNIX file system is removable file systems. Using the system command mount, you can attach removable volumes to a leaf in the file structure. There is virtually no distinction between the removable volume and the permanent file system.

Protection

Another innovation of UNIX was access control on files.

• Files created with owner name
• 6 bits for read/write/execute permissions for owner and others
• 7th bit can allow other users to temporarily become owner of the file

Super-User

• Regular users have limited access on a machine in some form or another
• Super-user is the highest privileged user on the machine, able to perform any action
• Usual constraints on the machine do not apply to super-user
• Should only allow one person access