User “ahmed” owns a directory, “stuff,” containing a text file called “ourstuff.txt” that he shares with users belonging to the group “staff.” Those users may read and change this file, but not delete it. They may not add other files to the directory. Others may neither read nor write or execute anything in “stuff.” What would appropriate ownerships and permissions for both the directory “stuff” and the file “ourstuff.txt” look like? (Write your answers in the form of “long listing” output.)
> Figure 21.3 shows the number of items in a system as a function of time. This can be viewed as the difference between an arrival process and a departure process, of the form a. On one graph, show the functions a(t) and d(t) that produce the n(t) shown
> Section 21.3 provided an intuitive argument to justify Little’s formula. Develop a similar argument to justify the relationship r=λTr.
> The continuous random variable R has a uniform density between 900 and 1,100, and 0 elsewhere. Find the probability that R is between 950 and 1,050.
> The mean and variance of X are 50 and 4, respectively. Evaluate the following: a. The mean of X2 b. The variance and standard deviation of 2X+3 c. The variance and standard deviation of - X
> In the carnival game known as chuck-a-luck, a player pays an amount E as an entrance fee, selects a number between one and six, and then rolls three dice. If all three dice show the number selected, the player is paid four times the entrance fee; if two
> A player tosses a fair die. If a prime number greater than 1 appears, he wins that number of dollars, but if a nonprime number appears, he loses that number of dollars. a. Denote the player’s gain or loss on one toss by the random variable X. Enumerate t
> A pair of fair dice (the probability of each outcome is 1/6) is thrown. Let X be the maximum of the two numbers that comes up. a. Find the distribution of X. b. Find the expectation E[X], the variance Var[X], and the standard deviation σX.
> The birthday paradox is a famous problem in probability that can be stated as follows: What is the minimum value of K such that the probability is greater than 0.5 that at least two people in a group of K people have the same birthday? Ignore February 29
> A taxicab was involved in a fatal hit-and-run accident at night. Two cab companies, the Green and the Blue, operate in the city. You are told that: 85% of the cabs in the city are Green and 15% are Blue A witness identified the cab as Blue The court test
> A patient has a test for some disease that comes back positive (indicating he has the disease). You are told that the accuracy of the test is 87% (i.e., if a patient has the disease, 87% of the time, the test yields the correct result, and if the patient
> What is the distinction between spatial locality and temporal locality?
> Let {Zn} be a set of uncorrelated real-valued random variables, each with a mean of 0 and a variance of 1. Define the moving average Yn=∑i=0KαiZn−i for constants α0, α1, …, αK. Show that Y is stationary and find its autocovariance function
> Suppose x(t) is a stochastic process with μ(t)=3 R(t1, t2)=9+4e −0.2| t1−t2 |.Determine the mean, variance, and covariance of the following random variables: Z=x(5) and W=x(8).
> An artificial example of a stochastic process is a deterministic signal x(t)=g(t). Determine the mean, variance, and autocorrelation of x(t).
> Consider a random variable X with the following distribution: Pr[X= −1]=0.25;Pr[X=0]=0.5; Pr[X=1]=0.25. Let Y=X2. a. Are X and Y independent random variables? Justify your answer. b. Calculate the covariance Cov(X, Y). c. Are X and Y uncorrelated? Justif
> Suppose X and Y each have only two possible values, 0 and 1. Prove if X and Y are uncorrelated, then they are also independent.
> Show that, all other things being equal, the greater the correlation coefficient of two random variables is, the greater the variance of their sum and the less the variance of their difference will be.
> You are asked to play a game in which I hide a prize in one of three boxes (with equal probability for all three boxes) while you are out of the room. When you return, you have to guess which box hides the prize. There are two stages to the game. First,
> In to retransmit lost packets, TFTP must keep a copy of the data it sends. How many packets of data must TFTP keep at a time to implement this retransmission mechanism?
> The TFTP specification (RFC 1350) states that the transfer identifiers (TIDs) chosen for a connection should be randomly chosen, so the probability that the same number is chosen twice in immediate succession is very low. What would be the problem of usi
> In Figure 19.11b, explain why the second line cannot simply read "request (j)=t." Figure 19.11b: (b) Second Part Notation send (j, access, end message of type access, with token, by process j token) broadcast (request, send message from process i of
> In Table 6.2, some of the Linux atomic operations do not involve two accesses to a variable, such as /. A simple read operation is obviously atomic in any architecture. Therefore, why is this operation added to the repertoire of atomic operations? Table
> For the token-passing mutual exclusion algorithm, prove that it: a. guarantees mutual exclusion. b. avoids deadlock. c. is fair
> In the token-passing mutual exclusion algorithm, is the timestamping used to reset clocks and correct drifts, as in the distributed queue algorithms? If not, what is the function of the timestamping?
> For the mutual exclusion algorithm of [RICA81], a. Prove that mutual exclusion is enforced. b. If messages do not arrive in the order that they are sent, the algorithm does not guarantee that critical sections are executed in the order of their requests.
> For Lamport’s algorithm, are there any circumstances under which Pi can save itself the transmission of a Reply message?
> For Figure 19.9, it is claimed that all four processes assign an ordering of to the two messages, even though q arrives before a at Work through the algorithm to demonstrate the truth of the claim Figure 19.9: PI P4 (a,1,1) I (q.1,4) Time (local clo
> In priority-based process scheduling, the scheduler only gives control to a particular process if no other process of higher priority is currently in the Ready state. Assume no other information is used in making the process scheduling decision. Also ass
> Some have argued that Unix/Linux systems reuse a small number of security features in many contexts across the system; while Windows systems provide a much larger number of more specifically targeted security features used in the appropriate contexts. Th
> What are the advantages and disadvantages of using a file integrity checking tool (e.g., tripwire). This is a program which notifies the administrator of any changes to files on a regular basis? Consider issues such as which files you really only want to
> TFTP’s time-out-and-retransmission scheme implies that all data packets will eventually be received by the destination host. Will these data also be received uncorrupted? Why or why not?
> We have seen that in order to deal with lost packets, TFTP implements a time-out-and-retransmit scheme, by setting a retransmission timer when it transmits a packet to the remote host. Most TFTP implementations set this timer to a fixed value of about fi
> What is the difference between a multiprocessor and a multicore system?
> TFTP, like most protocols, will never send an error packet in response to an error packet it receives. Why?
> The flushing policy is described in the subsection on process migration strategies in Section 19.1. a. From the perspective of the source, which other strategy does flushing resemble? b. From the perspective of the target, which other strategy does flush
> A user on a UNIX host wants to transfer a 4,000-byte text file to a Microsoft Windows host. In order to do this, he transfers the file by means of TFTP, using the netascii transfer mode. Even though the transfer was reported as being performed successful
> What is the limiting factor in the time required to transfer a file using TFTP?
> The previous version of the TFTP specification, RFC 783, included the following statement: All packets other than those used for termination are acknowledged individually unless a timeout occurs. The new specification revises this to say All packets othe
> Why does the TCP header have a header length field while the UDP header does not?
> The following FORTRAN program is to be executed on a computer, and a parallel version is to be executed on a 32- b computer cluster: L1: DO 10 I=1,1024 L2: SUM(I)=0 L3: DO 20 J=1, I L4: 20 SUM(I)=SUM(I)+I L5: 10 CONTINUE Suppose lines 2 and 4 each take t
> An application program is executed on a nine-computer cluster. A benchmark program takes time T on this cluster. Further, 25% of T is time in which the application is running simultaneously on all nine computers. The remaining time, the application has t
> Let be the percentage of program code that can be executed simultaneously by n computers in a cluster, each computer using a different set of parameters or initial conditions. α Assume the remaining code must be executed sequentially by a single processo
> A TCP segment consisting of 1,500 bits of data and 160 bits of header is sent to the IP layer, which appends another 160 bits of header. This is then transmitted through two networks, each of which uses a 24-bit packet header. The destination network has
> Figure 6.18 shows another solution to the dining philosophers problem using monitors. Compare to Figure 6.14 and report your conclusions. Figure 6.18: Figure 6.14: monitor dining_controller; enum states (thinking, hungry, eating) state [5]; cond ne
> List the major disadvantages of the layered approach to protocols.
> For this problem, first consider the case where you wish to order pizza for a party of guests. The layer models in Figure 17.8 can be used to describe the ordering and delivery of a pizza. The guest effectively places the order with the cook. The host co
> Consider user accounts on a system with a Web server configured to provide access to user Web areas. In general, this scheme uses a standard directory name, such as , in a user’s home directory. This acts as the user’s Web area if it exists. However, to
> In the traditional UNIX file access model, UNIX systems provide a default setting for newly created files and directories, which the owner may later change. The default is typically full access for the owner combined with one of the following: no access
> UNIX treats file directories in the same fashion as files; that is, both are defined by the same type of data structure, called an inode. As with files, directories include a 9-bit protection string. If care is not taken, this can create access control p
> Set user (SetUID) and set group (SetGID) programs and scripts are a powerful mechanism provided by Unix to support “controlled invocation” to manage access to sensitive resources. However, precisely because of this, it is a potential security hole, and b
> For the DAC model discussed in Section 15.3, an alternative representation of the protection state is a directed graph. Each subject and each object in the protection state is represented by a node (a single node is used for an entity that is both subjec
> Rewrite the function shown in Figure 15.2a so it is no longer vulnerable to a stack buffer overflow. Figure 15.2a: (a) Basic buffer overflow C code $ cc -g -o bufferl buffer1.c $ . /buffer1 START bufferl: str1 (START), str2 (START), valid (1) $ ./bu
> In the context of an IDS, we define a false positive to be an alarm generated by an IDS in which the IDS alerts to a condition that is actually benign. A false negative occurs when an IDS fails to generate an alarm when an alert-worthy condition is in ef
> What is cache memory?
> Consider an automated audit log analysis tool (e.g., swatch). Can you propose some rules which could be used to distinguish “suspicious activities” from normal user behavior on a system for some organization?
> Why is logging important? What are its limitations as a security control? What are pros and cons of remote logging?
> Assume a system with N job positions. For job position i, the number of individual users in that position is and the number of permissions required for the job position is a. For a traditional DAC scheme, how many relationships between users and permissi
> State some threats that result from a process running with administrator or root privileges on a system.
> Figure 13.12 is a listing of code intended for use on the eCos kernel. Figure 13.12: a. Explain the operation of the code. Assume thread B begins execution first, and thread A begins to execute after some event occurs. b. What would happen if the mutex
> The implementation of mutexes within the eCos kernel does not support recursive locks. If a thread has locked a mutex then attempts to lock the mutex again, typically as a result of some recursive call in a complicated call graph, then either an assertio
> Why does the eCos bitmap scheduler not support time slicing?
> In Table Q.1, what limitations should be placed in the use of/. Table Q.1: cyg_drv_mutex_destroy? Table Q.1 Device Driver Interface to the eCos Kernel: Concurrency cyg_drv_spinlock_init Initialize a spinlock in a locked or unlocked state. cyg_drv_sp
> Virtual machines are presented with storage in manners similar to physical machines via TCP/IP, Fibre-Channel, or iSCSI connections. There are features in virtualization that optimize memory and processor usage, and advanced features that can provide mor
> Providing additional bandwidth for virtualization servers initially involved additional network interface cards (NICs) for more network connections. With the advent of increasingly greater network backbone bandwidths (10Gbit/s, 40Gbit/s, and 100Gbit/s)
> Suppose there are two types of philosophers. One type always picks up his left fork first (a “lefty”), and the other type always picks up his right fork first (a “righty”). The behav
> How is the process address space handled during process migration?
> When virtualization first appeared in the x86 marketplace, many server vendors were skeptical of the technology and were concerned that consolidation would impact the sales of servers. Instead, server vendors found that they were selling larger, costlier
> Type 1 hypervisors operate directly on physical hardware without any intervening operating system. Type 2 hypervisors run as an application installed on an existing operating system. Type 1 hypervisors perform much better than Type 2 hypervisors since th
> Which type of process is generally favored by a multilevel feedback queuing scheduler—a processor-bound process, or an I/O-bound process? Briefly explain why.
> Consider the organization of a UNIX file as represented by the inode (see Figure 12.15). Assume there are 12 direct block pointers, and a singly, doubly, and triply indirect pointer in each inode. Further, assume the system block size and the disk sector
> In UNIX System V, the length of a block is 1 Kbyte, and each block can hold a total of 256 block addresses. Using the inode scheme, what is the maximum size of a file?
> Consider a hierarchical file system in which free disk space is kept in a free space list. a. Suppose the pointer to free space is lost. Can the system reconstruct the free space list? b. Suggest a scheme to ensure that the pointer is never lost as a res
> The discussion of eCos spinlocks included an example showing why spinlocks should not be used on a uni-processor system if two threads of different priorities can compete for the same spinlock. Explain why the problem still exists even if only threads of
> Techniques like memory over commit and page sharing permit virtual machines to be allocated more resources than are physically in a single virtualization host. Does this allow the aggregate of the virtual machines to perform more real work than a physica
> In Table Q.1, what should be the limitations on the use of / Explain? Table Q.1: cyg_drv_spinlock_destroy? Table Q.1 Device Driver Interface to the eCos Kernel: Concurrency cyg_drv_spinlock_init Initialize a spinlock in a locked or unlocked state. c
> Also in Table Q.1, it is recommended that / should be used sparingly, and in situations where deadlocks/livelocks cannot occur. Explain why. Table Q.1: cyg_drv_spinlock_spin Table Q.1 Device Driver Interface to the eCos Kernel: Concurrency cyg_drv_
> What characteristics distinguish the various elements of a memory hierarchy?
> With reference to the device driver interface to the eCos kernel (see Table Q.1), it is recommended that device drivers should use the / variants to claim and release spinlocks rather than the non- / variants. Explain why Table Q.1: intsave ()
> a. The TinyOS Resource interface does not allow a component that already has a request in the queue for a resource to make a second request. Suggest a reason. b. However, the TinyOS Resource interface allows a component holding the resource lock to re-re
> TinyOS’s scheduler serves tasks in FIFO order. Many other schedulers for TinyOS have been proposed, but none have caught on. What characteristics of the sensornet domain might cause a lack of need for more complex scheduling?
> Suggest pros and cons for fat client and thin client strategies.
> What are fat clients and thin clients, and what are the differences in philosophy of the two approaches?
> Discuss the rationale for locating applications on the client, the server, or split between client and server.
> What is the role of a communications architecture such as TCP/IP in a client/server environment?
> What distinguishes client/server computing from any other form of distributed data processing?
> What is client/server computing?
> What conditions are generally associated with the readers/writers problem?
> A fraction P of the traffic from a single exponential server is fed back into the input as shown in Figure 21.11. In the figure, Λ denotes the system throughput, which is the output rate from the server. Figure 21.11: a. Determine the syste
> What is the difference between demand cleaning and precleaning?
> List and briefly define three file allocation methods.
> What is RIOT?
> What requirements should an IoT OS satisfy?
> List and briefly define the principal components of an IoT-enabled thing.
> Define the Internet of Things.
> What is the purpose of the Sockets interface?
> What is TCP/IP?
> What is a protocol architecture?
> What is a protocol?
> How are multiple interrupts dealt with?
> What tasks are performed by the transport layer?
