Modern Operating Systems 4th edition Andrew S. Tanenbaum, Herbert Bos - Solutions

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An alternative algorithm for insertion into a B-tree is the following: As the insertion algorithm travels down the tree, each full node that is encountered is immediately split, even though it may turn out that the split was unnecessary. a. What is the advantage of this technique? b. What are the
Both the search and the insertion time for a B-tree are a function of the height of the tree. We would like to develop a measure of the worst-case search or insertion time. Consider a B-tree of degree d that contains a total of n keys. Develop an inequality that shows an upper bound on the height h
Ignoring overhead for directories and file descriptors, consider a file system in which files are stored in blocks of 16K bytes. For each of the following file sizes, calculate the percentage of wasted file space due to incomplete filling of the last block: 41,600 bytes; 640,000 bytes; 4.064,000
Directories can be implemented either as “special files” that can only be accessed in limited ways or as ordinary data files. What are the advantages and disadvantages of each approach?
Some operating systems have a tree–structured file system but limit the depth of the tree to some small number of levels. What effect does this limit have on users? How does this simplify file system design (if it does)?
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 result of a single memory failure.
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 the organization of a UNIX file as represented by the inode. Assume that there are 12 direct block pointers, and a singly, doubly, and triply indirect pointer in each inode. Further, assume that the system block size and the disk sector size are both 8K. If the disk block pointer is 32
What is an embedded system?
What are some typical requirements or constraints on embedded systems?
What are some of the key characteristics of an embedded OS?
Explain the relative advantages and disadvantages of an embedded OS based on an existing commercial OS compared to a purpose-built embedded OS.
What are the design goals for TinyOS?
What is a TinyOS component?
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-request the lock. This request is en-queued
The implementation of mutexes within the eCos kernel does not support recursive locks. If a thread has locked a mutex and then attempts to lock the mutex again, typically as a result of some recursive call in a complicated call graph, then either an assertion failure will be reported or the thread
Figure is a listing of code intended for use on the eCos kernel.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 unlock and wait code execution in the call to cyg_cond_wait, on line
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 the same priority can claim the same
Techniques like memory overcommit and page sharing permits 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 physical workload would be capable of on the same
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 there is no intervening layer to negotiate
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 servers. Why did this happen?
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), fewer NICs are necessary. What issues might
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 more efficient use of I/O resources. What do you
List and briefly define three classes of intruders.
In general terms, what are four means of authenticating a user’s identity?
Briefly describe the difference between DAC and RBAC.
What types of programming languages are vulnerable to buffer overflows?
List and briefly describe some of the defenses against buffer overflows that can be used when compiling new programs.
List and briefly describe some of the defenses against buffer overflows that can be implemented when running existing, vulnerable programs.
State some threats that result from a process running with administrator or root privileges on a system.
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 effect. Using the following diagram, depict two
Rewrite the function shown in Figure so that it is no longer vulnerable to a stack buffer overflow.
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 subject and object). A directed line from a subject
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 bugs in such programs have led to many
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
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 problems. For example, consider a file with
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 for group and other, read/execute access for
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 public_html, in a user’s home directory. This acts as the user’s Web area if it exists. However, to allow the Web server to
Assume a system with N job positions. For job position i, the number of individual users in that position is Ui and the number of permissions required for the job position is Pi.a. For a traditional DAC scheme, how many relationships between users and permissions must be defined?b. For an RBAC
Why is logging important? What are its limitations as a security control? What are pros and cons of remote logging?
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?
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 change rarely, which files may change more
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. This may be seen as a trade-off between
What distinguishes client/server computing from any other form of distributed data processing?
Discuss the rationale for locating applications on the client, the server, or split between client and server.
What are fat clients and thin clients, and what are the differences in philosophy of the two approaches?
Suggest pros and cons for fat client and thin client strategies.
Explain the rationale behind the three-tier client/server architecture.
What is middleware?
List some benefits and disadvantages of blocking and non-blocking primitives for message passing.
List some benefits and disadvantages of non-persistent and persistent binding for RPCs.
List some benefits and disadvantages of synchronous and asynchronous RPCs.
List and briefly define four different clustering methods.
Let a 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. Assume that the remaining code must be executed sequentially by a single processor. Each processor has an execution rate
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 to run on a single computer.a. Calculate the
The following FORTRAN program is to be executed on a computer, and a parallel version is to be executed on a 32-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 two machine cycle times,
What is the difference between kernel and user mode? Explain how having two distinct modes aids in designing an operating system.
A 255-GB disk has 65,536 cylinders with 255 sectors per track and 512 bytes per sector. How many platters and heads does this disk have? Assuming an average cylinder seek time of 11 ms, average rotational delay of 7 msec and reading rate of 100 MB/sec, calculate the average time it will take to
Consider a system that has two CPUs, each CPU having two threads (hyperthreading). Suppose three programs, P0, P1, and P2, are started with run times of 5, 10 and 20 msec, respectively. How long will it take to complete the execution of these programs? Assume that all three programs are 100% CPU
A computer has a pipeline with four stages. Each stage takes the same time to do its work, namely, 1 nsec. How many instructions per second can this machine execute?
Consider a computer system that has cache memory, main memory (RAM) and disk, and an operating system that uses virtual memory. It takes 1 nsec to access a word from the cache, 10 nsec to access a word from the RAM, and 10 ms to access a word from the disk. If the cache hit rate is 95% and main
When a user program makes a system call to read or write a disk file, it provides an indication of which file it wants, a pointer to the data buffer, and the count. Control is then transferred to the operating system, which calls the appropriate driver. Suppose that the driver starts the disk and
Why is the process table needed in a timesharing system? Is it also needed in personal computer systems running UNIX or Windows with a single user?
Is there any reason why you might want to mount a file system on a nonempty directory? If so, what is it?
In Section 1.4, nine different types of operating systems are described. Give a list of applications for each of these systems (one per operating systems type).
For each of the following system calls, give a condition that causes it to fail: fork, exec, and unlink.
Can the Count = write(fd, buffer, nbytes); call return any value in count other than nbytes? If so, why?
Suppose that a 10-MB file is stored on a disk on the same track (track 50) in consecutive sectors. The disk arm is currently situated over track number 100. How long will it take to retrieve this file from the disk? Assume that it takes about 1 ms to move the arm from one cylinder to the next and
What is the essential difference between a block special file and a character special file?
In the example given in Fig. 1-17, the library procedure is called read and the system call itself is called read. Is it essential that both of these have the same name? If not, which one is more important?
To a programmer, a system call looks like any other call to a library procedure. Is it important that a programmer know which library procedures result in system calls? Under what circumstances and why?
Figure 1-23 shows that a number of UNIX system calls have no Win32 API equivalents. For each of the calls listed as having no Win32 equivalent, what are the consequences for a programmer of converting a UNIX program to run under Windows?
What is the difference between timesharing and multiprogramming systems?
A portable operating system is one that can be ported from one system architecture to another without any modification. Explain why it is infeasible to build an operating system that is completely portable. Describe two high-level layers that you will have in designing an operating system that is
Explain how separation of policy and mechanism aids in building microkernel-based operating systems.
Here are some questions for practicing unit conversions: (a) How long is a nanoyear in seconds? (b) Micrometers are often called microns. How long is a megamicron? (c) How many bytes are there in a 1-PB memory? (d) The mass of the earth is 6000 yottagrams. What is that in kilograms?
To use cache memory, main memory is divided into cache lines, typically 32 or 64 bytes long. An entire cache line is cached at once. What is the advantage of caching an entire line instead of a single byte or word at a time?
On early computers, every byte of data read or written was handled by the CPU (i.e., there was no DMA). What implications does this have for multiprogramming?
Instructions related to accessing I/O devices are typically privileged instructions, that is, they can be executed in kernel mode but not in user mode. Give a reason why these instructions are privileged.
The family-of-computers idea was introduced in the 1960s with the IBM System/360 mainframes. Is this idea now dead as a doornail or does it live on?
One reason GUIs were initially slow to be adopted was the cost of the hardware needed to support them. How much video RAM is needed to support a 25-line × 80-row character monochrome text screen? How much for a 1200 × 900-pixel 24-bit color bitmap? What was the cost of this RAM at 1980 prices
There are several design goals in building an operating system, for example, resource utilization, timeliness, robustness, and so on. Give an example of two design goals that may contradict one another.
In Fig. 2-2, three process states are shown. In theory, with three states, there could be six transitions, two out of each state. However, only four transitions are shown. Are there any circumstances in which either or both of the missing transitions might occur?
In the text it was stated that the model of Fig. 2-11(a) was not suited to a file server using a cache in memory. Why not? Could each process have its own cache?
In Fig. 2-8, a multithreaded Web server is shown. If the only way to read from a file is the normal blocking read system call, do you think user-level threads or kernel-level threads are being used for the Web server? Why?
In the text, we described a multithreaded Web server, showing why it is better than a single-threaded server and a finite-state machine server. Are there any circumstances in which a single-threaded server might be better? Give an example.
In Fig. 2-12 the register set is listed as a per-thread rather than a per-process item. Why? After all, the machine has only one set of registers.
Why would a thread ever voluntarily give up the CPU by calling thread yield? After all, since there is no periodic clock interrupt, it may never get the CPU back.
Can a thread ever be preempted by a clock interrupt? If so, under what circumstances? If not, why not?
In this problem you are to compare reading a file using a single-threaded file server and a multithreaded server. It takes 12 msec to get a request for work, dispatch it, and do the rest of the necessary processing, assuming that the data needed are in the block cache. If a disk operation is
Suppose that you were to design an advanced computer architecture that did process switching in hardware, instead of having interrupts. What information would the CPU need? Describe how the hardware process switching might work.
In the discussion on global variables in threads, we used a procedure create global to allocate storage for a pointer to the variable, rather than the variable itself. Is this essential, or could the procedures work with the values themselves just as well?
Consider a system in which threads are implemented entirely in user space, with the run-time system getting a clock interrupt once a second. Suppose that a clock interrupt occurs while some thread is executing in the run-time system. What problem might occur? Can you suggest a way to solve it?
Does the busy waiting solution using the turn variable (Fig. 2-23) work when the two processes are running on a shared-memory multiprocessor, that is, two CPUs sharing a common memory?
Does Peterson's solution to the mutual-exclusion problem shown in Fig. 2-24 work when process scheduling is preemptive? How about when it is nonpreemptive?
Can the priority inversion problem discussed in Sec. 2.3.4 happen with user-level threads? Why or why not?
In Sec. 2.3.4, a situation with a high-priority process, H, and a low-priority process, L, was described, which led to H looping forever. Does the same problem occur if roundrobin scheduling is used instead of priority scheduling? Discuss.
In a system with threads, is there one stack per thread or one stack per process when user-level threads are used? What about when kernel-level threads are used? Explain.
When a computer is being developed, it is usually first simulated by a program that runs one instruction at a time. Even multiprocessors are simulated strictly sequentially like this. Is it possible for a race condition to occur when there are no simultaneous events like this?
On all current computers, at least part of the interrupt handlers are written in assembly language. Why?

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Modern Operating Systems 4th edition Andrew S. Tanenbaum, Herbert Bos - Solutions

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