Permissions

• Most operating systems -- including Mac OS, other UNIX-based systems, and many versions of Windows -- support file permissions. This means that the "owner" of a file gets to decide which users can do what to it. A file owner may decide that everyone can read a file, but that only he can write to it, or he may lock the file up completely to every user but him.
  
  

Permission Error

• A permission error is returned when a user attempts to read or write a file for which he doesn't have the necessary permission. It might be possible for the user to resolve the problem himself -- for example, if the file is simply set to "read-only" as a safety measure, but the user has the power to change permissions, he can give himself permission to modify the file.
  
  

Changing Permissions

• How to change permissions depends on your operating system. Check your OS documentation or search online for the relevant instructions. Mac OS has the advantage of using a permissions system identical to the venerable UNIX system, and is thus standardized and useful to learn. Windows uses its own approximation of this system.