Suggest an efficient scheme for maintaining a per-user protection scheme. That is, the system maintains one directory per user, and that directory lists all the objects to which the user is allowed access. Your design should address the needs of a system with 1000 users, of whom no more than 20 are active at any time. Each user has an average of 200 permitted objects; there are 50,000 total objects in the system

A Unix process may call another process without fully trusting it. In this situation, the caller may want the called process to have access only to the objects that the caller explicitly passes to it, and not to arbitrary files owned by the caller. One possible solution is to create a restricted user ID, and execute the called process under this restricted UID. In some flavors of UNIX, any process can use setuid() to set its EUID to RUID. Are thereany security implications for the situation described above, where one process calls another under a restricted UID? Assume that either the caller, or the callee may be malicious.

Suggest an efficient scheme for maintaining a per-user protection scheme.That is, the system maintains one directory per user, and that directory lists allthe objects to which the user is allowed access. Your design should address theneeds of a system with 1000 users, of whom no more than 20 are active at anytime. Each user has an average of 200 permitted objects; there are 50,000 totalobjects in the system.

Write a Python script that starts 3 counters using 3 new processes. All processes should be based on a single function (i.e. "counting()"). The function should take 1 parameter representing the target of the counter (i.e. if count_to=12 then the process should print 1,2,3,4...,12 ). Start each process with a different target of the counter.   How many objects does the gc track in each process before and after the counter completes its task?

Suppose that an operating system supports two kinds of sequential processes: high-priority interactive processes, and low-priority non-interactive processes. The behavior of the high-priority processes is to alternate between periods of computation of duration Tc and periods of blocking (waiting for input) of duration Tb. The behavior of the low-priority processes is to compute constantly, with no blocking. The operating system’s scheduling policy is round-robin with a quantum q, where Tc < q. Scheduling decisions are made only when a quantum expires, or when the running process blocks. The scheduler selects a low-priority process to run only if no high-priority processes are ready. Suppose there is one high-priority process and one low-priority process in the system, and that both processes will run for a long time. For what fraction of the time does the low-priority process run?

Consider a file system that uses a modifed contiguous-allocation scheme with support for extents. A file is a collection of extents, with each ex- tent corresponding to a contiguous set of blocks. A key issue in such systems is the degree of variability in the size of the extents. What are the advantages and disadvantages of the following schemes: a. All extents are of the same size, and the size is predetermined. b. Extents can be of any size and are allocated dynamically. c. Extents can be of a few fixed sizes, and these sizes are predeter- mined.

Consider a computer environment in which there are 4 magnetic drives, 2 printers, 3 scanners, and 1 optical drive. Three processes P1, P2, P3 are using these resources. At any point in time, the allocations and requests for these resources are as follows. Allocations: Magnetic drive Printer Scanner Optical drive P1 1 P2 2 1 P3 1 Requests: Magnetic drive 2 Printer Scanner Optical drive P1 1 P2 1 1 P3 2 1 Is there any way that the processes can complete without deadlock? If yes, explain how. If not, explain why not.

Suppose a system has 5 processes, P = {P1, P2, P3, P4, P5}, and 4 resources, R = {R1, R2, R3, R4}, where there are 2 instances of R1, 1 instance of R2, 3 instances of R3, and 3 instances of R4. The current state of the system is defined by the following requests and assignments: P1 is requesting an instance of R3 and has been assigned an instance of R2; P2 is requesting an instance of R1 and has been assigned an instance of R3; P3 is requesting an instance of R4 and has been assigned an instance of R1 and an instance of R3; P4 is requesting an instance of R3; P5 is requesting an instance of R2 and has been assigned an instance of R4. Is there deadlock in this system? (Explicitly state yes, there’s deadlock or no, there isn’t.) If applicable, draw a wait-for graph or resource-allocation graph, and use the appropriate graph to justify your answer. If you conclude there is no deadlock, your justification should contain a sequence of execution for the processes which shows that…

Given a directory tree of a file system, if /usr/jeff is the working directory, what is the absolute path name for the file whose relative path name is ../ast/z?

The WIMP layout is used in computer displays. Most WIMP implementations adhere to the Desktop metaphor, which links common actions to their physical counterparts. A file may be relocated by selecting it and dragging it to a new location, such as a folder or a filing cabinet. Provide two actions and their corresponding real-world instances.