COP 4600 - Final Exam With Correct Solutions

COP 4600 - Final Exam What must I/O devices be connected to in order to do anything? - ANS A computer What is a port? - ANS A set of wires that connects an I/O device and the computer. A device that allows other devices to hook up to it in turn is said to support what? - ANS Daisy-chained devices What is a bus? - ANS A common set fo wires used by more than one I/O device If devices connect to ports, what do ports connect to? - ANS Buses What is a controller? - ANS The electronics that manage a port, bus or I/O device What does the operating system actually talk to? - ANS The device's controller What is a data in register? - ANS Allows the computer to get input from the device What is a data out register? - ANS Allows the computer to send output to the device What is a status register? - ANS Indicates the current state of the device, including whether the current command has completed, whether the data registers are ready, and whether there is an error. What is a control register? - ANS A register that is used to send commands to the device What does the interrupt/trap mechanism handle? - ANS User-process calls for I/O, and notifications for those calls. Notifications from hardware about I/O completion, memory exceptions, arithmetic exceptions (divide by zero), and privilege exceptions. What is required in order for direct memory access to work? - ANS Device controllers must be given their own channel to system memory, with its own control registers. What is a device driver? - ANS A piece of software intended to handle interfacing with a particular device's controller. What are some I/O device characteristics? - ANS Stream versus block, sequential versus random, synchronous versus asynchronous, sharable versus dedicated, read/write versus read-only write-only, speed of operation. What are the fundamental functions of block devices? - ANS Read, write, and seek. What are fundamental functions of character-stream devices? - ANS Get and put (often still mapped to read and write with bufferring to allow multiple bytes to be read and written) What is a socket interface? - ANS Provides a file-like metaphor for reading and writing to a network connection What are the three main functions of hardware clocks? - ANS Report the current ime, report the elapsed time, and set an interval timer to report in the future. What are clocks used by the OS for, at a minimum? - ANS To preempt processes, flush cache buffers, and to report the failure of timed-out network connections. What is the device status table? - ANS A table that is used to keep track of each device and related pending request queues. What is a spool? - ANS A special-purpose buffer that serves entire coherent jobs. What is the print spool? - ANS The OS accepts jobs quickly on the printer's behalf, and presents them to the printer in order. What are disks? - ANS Secondary storage devices that represent both the effective bottom of the memory hierarchy and the most obvious I/O devices. What are the three types of disks? - ANS Magnetic disks, optical disks, and solid state disks. What are magnetic disks? - ANS Fixed disks that are made up of a series of plateers. The platters are divided into circular tracks, and the track are then divided into sectors, and the collection of tracks at the same distance from the center is referred to as a cylinder. What allows the disk to run? - ANS A drive motor spins it What are the two important speed metrics for magnetic disks? - ANS Transfer rate and the random accss time. What is the transfer rate? - ANS The effective rate of data flow between the disk and the computer. What is the random access time? - ANS Equal to the seek time plus the rotational latency. What is the seek time? - ANS The time is takes to move the disk arm to the right of the cylinder. What is the rotational latency? - ANS The time it takes the right sector to rotate to the disk head. Most personal disks nowadays are host attached. What does this mean? - ANS ATA in its various forms for magnetic disks and low-end SSDs, PCI Express for high-end SSDs, USB for low-end external drives, or Thunderbolt for high-end external drives. How does network attached storage work? - ANS By using standard networking protocols to provide storage over the network. This typically means NFS/CIFS network devices or shares. What is low level formatting? - ANS The process of writing the storage structures that order the disk at the sector level. What is the partition referred to where code from is loaded by the chain of bootstrap programs? - ANS Boot partition What is RAID? - ANS Redundant array of independent disks How do RAID arrays help? - ANS They increase the reliability of data by implementing redundancy and also increase performance of the data retrieval and manipulation process by storing it across multiple devices. How does RAID 0 work? - ANS Strips data block-by-block across multiple disks What are the performance ratings for RAID 0? - ANS Write and Read performance are theoretically equal to the combined disks, severe decrease in reliability, disk space of all disks combined. How does RAID 1 work? - ANS Mirrors data across multiple disks, writing identical data to each disk in the array What are the performance ratings for RAID 1? - ANS Write performance is equal to a single disk, read performance is equal to RAID 0, all but 1 disk must fail for data to be lost, disk space of a single disk. What is the final disk used for in RAID 5 and 6? - ANS Used to store a parity block What is the difference between RAID 5 and RAID 6? - ANS RAID 6 does the same thing, but uses two disks for parity instead of one. What is typically the primary logical, user-facing unit of secondary storage? - ANS A file What is a file at minimum? - ANS A named, sequential array of bytes. What are files stored in? - ANS Volumes What are volumes stored in? - ANS Partitions What are the different attributes that files can have? - ANS Name, identifier, type, location, size, protection, last-access information What are the different operations that can be performed on a file? - ANS creation, writing, reading, seeking, deleting, truncating What is truncating? - ANS Like deleting, but preserves the directory entry. What is implicit per-file state information? - ANS Where the file is in the file system What are the three operations that require explicit per-file, per-process state? (the position pointer) - ANS reading, writing, and seeking Where is the metadata for files contained? - ANS The file table, maintained by the operating system. What is an open count? - ANS A variable used by the operating system to determine when all the processes using a file have closed it. On the disk where are files stored? - ANS In sectors What does the directory contain at a minimum? - ANS A file's core attributes -- name, identifier, type, location, size, protection, and last-access info What is the primary job of the directory? - ANS Allowing the operating system to find files What is the secondary job of the directory? - ANS Allowing the user to find files At a minimum, the directory must let us...? - ANS Locate a file, create a file, delete a file, list the files, rename a file, traverse the file system What are soft or symbolic links? - ANS Pointers from a directory to another directory where the file actually resides. These are links to names and not the actual files What are hard links? - ANS Actual, equal-footing valid references to the file itself What are mount points? - ANS Places where file systems are located When it comes to file sharing, at a minimum, the operating system must keep track of? - ANS The owner of a given file, which other users are allowed to access a file, what those others are allowed to do with the file. What do distributed file system protocols allow us to do? - ANS Provide the ability to actually mount remote file systems -- or subdirectories of them -- as we would mount locally attached storage. What are some file operations the might have separate access requirements? - ANS Reading from a file, writing to a file, executing a program, deleting a file, and listing a directory. For directories, what does the execute permission allow for? - ANS Allows items in the directory to be located without reading it, if their name is known. What are the classes of users on UNIX-like systems? - ANS User, group, and others What are access control lists? - ANS Allow any set of users to be arbitrarily granted a given set of access rights to any file What are some attributes that are common to essentially all file systems? - ANS divide disks into partitions, format partitions using file systems, file systems have hierarchical directories, directories provide references to files, file are stored in blocks, blocks are one or more sectors on disk. What happens when the application makes file requests through the system libraries? - ANS requests arrvie at logical file system, logical file system the consults the fire organization module which manages the actual location of files on the physical disk, including free space, which then consults the basic file system, which brokers the commands to actually read and write blocks on the physical disk, by consulting the I/O control layer, which consists of the device drivers and interrupt handlers that then consult the disk. What does the boot control block contain? - ANS Information necessary to boot an operating system from a partition What does the volume control block contain? - ANS Contains (at least) the number of blocks in the partition, the size of the blocks, free-block information, and information about file control blocks. Every file has a file control block that consists of what? - ANS Permissions and access control, dates, size, information required to locate the file What is an example of a partition that doesn't contain a file system? - ANS Swap space or high-end databases What are virtual file systems? - ANS OS-internal programming interfaces that allow support for new fil systems to be easily added to the kernel A VFS specification describes a means by which a file system will provide, in part...? - ANS Information to the kernel about files on the disk, open files, file systems, directory entries, and a means of traversing, reading, and writing directory entries, and opening, closing, reading, and writing files. Do virtual file systems have to reside on disks? - ANS Nope What is contiguous allocation? - ANS Requires that all the blocks of a file reside one next to another on the disk, in order What is linked allocation? - ANS Each file is a linked list of disk blocks. Each block contains a pointer to the next blocks. Seeking is slow O(n) What is the file allocation table method? - ANS implements a linked allocation, but keeps all the pointers at the beginning of the disk. What is indexed allocation? - ANS Alternate method of solving the seek problem. Each file is given its own index block, linked to by its FCB. The nth entry in the blocks points to the nth block of a file. What are unified memory techniques? - ANS Where all physical memory not in use by processes is available for use by the disk cache. When must synchronous writes occur? - ANS must occur immediately When can asynchronous writes occur? - ANS In any order What are consistency checking programs? - ANS Programs that examine partitions and recover them from standard patterns of inconsisten metadata. What is journaling? - ANS Greatly alleviates the problem of inconsistent metadata by synchronously writing to a journal at a later time and are then updated asynchronously on the disk from there. What happens when a crash occurs if journaling is enabled? - ANS The system completes all changes that are still in the journal. Does journaling improve performance? - ANS Yes, by simplifying the need for synchronous writing. What are the three types of addressing when it comes to message passing? - ANS Symmetric, asymmetric, and mailbox Symmetric? - ANS message = receive(P) Asymmetric? - ANS receive(var message, var sender) Mailbox? - ANS send(M, message) message = receive(M) Is sending/receiving a blocking or non-blocking procedure? - ANS Either or What is a blocking procedure? - ANS forces a process to wait until there is space in the send queue What is a non-blocking send? - ANS fails if there isn't space in the send queue What is a blocking receive? - ANS forces a process to wait until data is available What is a non-blocking receive? - ANS fails if no data is available What are pipes? - ANS implements message passing using the file metaphor How do ordinary pipes communicate? - ANS Between parent and child processes How do named pipes communicate? - ANS Can communicate between any number of processes Where do pipes live? - ANS In the file system -- can be opened, closed, read, and written by any process with permissions to do so What are sockets? - ANS Metaphors for the pipes that go between machines on a network How many sockets does each active network connection have? - ANS Two Instead of a filename, a socket has what? - ANS A network address and a por What is the Open Systems Interconnect Model? - ANS Defines every layer of networking -- including the data to be exchanged What does the session layer do? - ANS defines the exchange of the data What does the presentation layer do? - ANS Defines the format of the data What does the application layer do? - ANS Determines the semantics and usage of the data. What is a medium? - ANS What packets travel over What is the physical layer? - ANS Transmitters and receivers that in turn render symbols into physical signals, commit the signals tot he medium, retrieve the signals from the medium, and convert the signals back into symbols. What layer devices are the radios on your wireless networking adapters? - ANS Physical-layer What is the data link layer? - ANS The protocl layer that transmits and receives data between nodes in a single network What is Media Access Control (MAC)? - ANS Addresses frames between devicdes on the same network and manages collisions between multiple devices trying to use the network at once. Network adapters, switches, and hubs are ______ layer devices? - ANS Data-link What is the network layer? - ANS Provides transmission of data packets between points on an arbitrarily large network of networks What is the internet protocol? - ANS Allows individual networks to be interconnected, and packets to be routed between these sub-networks. What is the transport layer? - ANS Provides reliable transmission of data packets between points on an arbitrarily large network When you open a socket, what are you using? - ANS TCP What is the application layer? - ANS What provide network services to the user Which network layers are exclusively handled by the OS? - ANS Transport and Network layers What is authentication? - ANS Determining who a user is What is LDAP? - ANS The lightweight directory access protocol -- an example of a directory service that holds info about users, including passwords. What is Kerberos? - ANS A key-based protocol specificall designed for authentication What is the first thing that you do when you log into any server within a Kerberos realm? - ANS Communicate with an authentication server What does the authentication server in a Kerberos realm do? - ANS Encrypts an authentication packet using a key derived from your password and sends it to you Is your password ever sent over the network when using Kerberos authentication? - ANS No When you obtain your session key from a Kerberos auth packet, who do you then send that session key to? - ANS Ticket Granting / Authorization server What is shibboleth? - ANS Similar to kerberos but designed for use over the web by not requiring servers to belong to specific realms What are the first major source of large-scale password breaches? - ANS Password files obtained from servers with bad hashing algorithms What is the second major source of large-scale password breaches? - ANS If an attacker obtains a hashed password file they can run the hashing algorithm with a list of simple words and bruteforce their way into the system by testing the algorithm with the list of words. What are the three main factors the affect the strength of passwords? - ANS Longer passwords are stronger, passwords that use more types of characters, and randomness is much harder to quantify What is two-factor authentication? - ANS Using two factors of authentication to authenticate a user... What is a time-based one-time password? - ANS A password that is used for standard 2FA What is the hierarchy of security? - ANS Keyfobs, cell phoe apps, and then any form of 2FA is etter than no 2FA What are you trying to protect in the first place when it comes to security? - ANS Confidentiality, integrity, and availability. What are targets? - ANS What the attackers want, or want to disrupt What is the attack surface? - ANS Where you are exposed to the attack What are threats? - ANS How you can be attacked What is mitigation? - ANS How you avoid or neutralize attacks Where are the five easy attack surfaces that attackers try to utilize? - ANS Physical computer, computer's network, computer's software, online accounts, yourself (social engineering) What are the two kinds of mitigation measures? - ANS Administrative measures and technical measures What are administrative measures? - ANS What you don't do What are technical measures? - ANS the tools that you use