File system permissions are your data’s first line of defense in a multiuser environment. A well-managed permission scheme ensures that your data is accessible and modifiable only by the proper people. The file system, after all, is the gateway to your data. An ineffective permission scheme is the equivalent of handing your data out to anyone who would express interest in it, or even worse, allowing them to destroy it. Furthermore, poorly implemented permissions can serve a different evil, preventing honest, hardworking Joe from accessing either his own documents or documents created by his collaborators.