Types of Access

• The need to protect files is a direct result of the ability to access files.
  • Systems that do not permit access to the files of other users do not need protection.
  • Alternatively, we could provide free access with no protection.
• Both approaches are too extreme for general use. What is needed is controlled access.
• Several different types of operations may be controlled:
  • Read.
  • Write.
  • Execute. Load the file into memory and execute it.
  • Append. Write new information at the end of the file.
  • Delete.
  • List. List the name and attributes of the file.
• Other operations, such as renaming, copying, and editing the file, may also be controlled. These higher-level functions may be implemented by a system program that makes lower-level system calls.