Introducing UNIX and Linux

Files

Overview
The UNIX directory hierarchy
Filesystems
Manipulating files
      Creating directories
      Creating files
      links
      'Dot' files
Protecting files
      Groups
      File access control
      Changing privileges
File contents
      Text files
      Comparing files
      Filtering files
      Non-text files
Printing files
File archives and file compression
Other relevant commands
Summary
Exercises

Protecting files

Some data you store on the machine should not be readable by other users. If you are doing a programming assignment for your course, for example, other students should not read it. If your institution has purchased software which has conditions attached to its use (as is often the case nowadays) it may be necessary to restrict its use to a specific group of users.

You may also wish to prevent yourself accidentally overwriting a file and destroying important data. In this section we look at a basic mechanism for enabling file protection. First, however, we must explore UNIX' formal notion of a group of users, which is important for understanding how to protect files.