File Protection and Permissions

No one wishes to have people mess up with their files, either carelessly or intentionally. For this purpose, the operating system enforces a permissions system that tells who (which users) can do what (what actions) to which files.

The goal of such access control policies is to ensure the protection of files from the actions of other users.

Every OS has different access control policies. For example, each system defines different types of 'actions' that can be applied to files, among which are reading, writing, appending to, executing, deleting, and listing the names (and other metadata) of files.

Some systems can apply passwords, either to individual files, to specific sub-directories, or to the entire file system.