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Chapter 2. Managing Multiple Users > WHY WE HAVE MULTIPLE USERS - Pg. 32

32 CHAPTER 2 Managing Multiple users a consistent meaning on every workstation and server on the network, extending the user's sandbox to cover file servers, mail services and so on provided by remote systems. The user account paradigm on modern UNIX systems including Mac OS X is largely unchanged from that of the workstations of the 1980s. We shall see below how the concept of multiple users provides security protection to the system our applications are running on, how to fit in and potential risks introduced by multi-user systems. CAvEAT foR IPHoNE DEvEloPERS The UNIX multiple-user paradigm is present in the implementation of the iPhone OS, but is not exposed via the iPhone SDK. Applications have their user accounts set up for them by the operat- ing system, which then uses alternative access control methods to prevent disruption of each app by the other. The iPhone sandbox is described in "Playing in the Sandbox" in Chapter 4. The rest of this chapter may provide an interesting diversion to iPhone developers interested to see how a more general-purpose UNIX system works, but none of the rest of this chapter is directly applicable to iPhone apps. WHy WE HAvE MulTIPlE uSERS