Berkeley Software Distribution (BSD) Interview Questions & Answers

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Berkeley Software Distribution (BSD) Interview Questions & Answers

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Berkeley Software Distribution (BSD) Interview Questions

Berkeley Software Distribution (BSD) Interview Questions
    1. Question 1. What Are The Key Objects Oriented Concepts Used By Windows Nt?

      Answer :

      • Encapsulation
      • Object class
      •  instance

    2. Question 2. Is Windows Nt A Full Blown Object Oriented Operating System?

      Answer :

      No Windows NT is not so, because its not implemented in object oriented language and the data structures reside within one executive component and are not represented as objects and it does not support object oriented capabilities.

    3. Question 3. What Is A Drawback Of Mvt?

      Answer :

      It does not have the features like ability to support multiple processors virtual storage source level debugging

    4. Question 4. What Is Process Spawning?

      Answer :

      When the OS at the explicit request of another process creates a process, this action is called process spawning

    5. Question 5. List Out Some Reasons For Process Termination?

      Answer :

      • Normal completion
      • Time limit exceeded
      • Memory unavailable
      • Bounds violation
      • Protection error
      • Arithmetic error
      • Time overrun
      • I/O failure
      • Invalid instruction
      • Privileged instruction
      • Data misuse
      • Operator or OS intervention
      • Parent termination.

    6. Question 6. What Are The Reasons For Process Suspension?

      Answer :

      Reasons for Process Suspension:

      • Swapping: OS needs to release some memory
      • Other OS reason: suspicion of causing problem or system performance
      • Interactive user request: debugging or other resource reasons
      • Timing:submit but hold (suspend) a process until another has completed

       

    7. Question 7. What Is Process Migration?

      Answer :

      It is the transfer of sufficient amount of the state of process from one machine to the target machine

    8. Question 8. What Are Rings In Windows Nt?

      Answer :

      Windows NT uses protection mechanism called rings provides by the process to implement separation between the user mode and kernel mode.

    9. Question 9. State And Explain About What An Operating System Is?

      Answer :

      Operating system is made up of basically two functions they are managing resources and extending the machine. Operating system gives a user interface through which he can perform various functions. It acts as a medium for communication between the machine and user.

    10. Question 10. Explain About What A Signal Is?

      Answer :

      A signal is a software mechanism that informs a process of the occurrence of asynchronous events. It does not employ priorities but it is more or less similar to a hardware interrupt. That is, all signals are treated equally. Signals that occur at the same time are presented to a process one at a time, with no particular ordering.

    11. Question 11. What Design And Management Issues Are Raised By The Existence Of Concurrency?

      Answer :

      The operating system must be able to keep track of the various active processes.

      The operating system must allocate and de-allocate various resources for each active process.

      The operating system must protect the data and physical resources of each process against unintended interference by other processes. This involves techniques that relate to memory, files, and I/O devices.

      The results of a process must be independent of the speed at which the execution is carried out relative to the speed of other concurrent process.

    12. Question 12. What Are The Contexts In Which Concurrency May Occur?

      Answer :

      Concurrency may arise in three different contexts.

      1. Multiple applications: -Processing time of the computer to be dynamically shared among a number of active jobs or applications
      2. Structured application: - With principles of modular design and structured programming some applications can be effectively implemented as a set of concurrent process.
      3. Operating system structure: -The same structuring advantages apply to the system programmer.

    13. Question 13. What Is A Data Register And Address Register?

      Answer :

      Data registers can be assigned to a variety of functions by the programmer. They can be used with any machine instruction that performs operations on data.

      Address registers contain main memory addresses of data and instructions or they contain a portion of the address that is used in the calculation of the complete addresses.

    14. Question 14. What Is Dispatcher?

      Answer :

      Dispatcher module gives control of the CPU to the process selected by the short-term scheduler; this involves: Switching context, Switching to user mode, Jumping to the proper location in the user program to restart that program, dispatch latency ? time it takes for the dispatcher to stop one process and start another running.

    15. Question 15. What Is Dram? In Which Form Does It Store Data?

      Answer :

      DRAM is not the best, but it?s cheap, does the job, and is available almost everywhere you look. DRAM data resides in a cell made of a capacitor and a transistor. The capacitor tends to lose data unless it?s recharged every couple of milliseconds, and this recharging tends to slow down the performance of DRAM compared to speedier RAM types.

    16. Question 16. What Is Fragmentation? Different Types Of Fragmentation?

      Answer :

      Fragmentation occurs in a dynamic memory allocation system when many of the free blocks are too small to satisfy any request.

      External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous.

      Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks. Allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used

    17. Question 17. What Is The Cause Of Thrashing? How Does The System Detect Thrashing?

      Answer :

      Once it detects thrashing, what can the system do to eliminate this problem? - Thrashing is caused by under allocation of the minimum number of pages required by a process, forcing it to continuously page fault. The system can detect thrashing by evaluating the level of CPU utilization as compared to the level of multiprogramming. It can be eliminated by reducing the level of multiprogramming.

    18. Question 18. What Is The Difference Between Hard And Soft Real-time Systems?

      Answer :

      A hard real-time system guarantees that critical tasks complete on time. This goal requires that all delays in the system be bounded from the retrieval of the stored data to the time that it takes the operating system to finish any request made of it. A soft real time system where a critical real-time task gets priority over other tasks and retains that priority until it completes. As in hard real time systems kernel delays need to be bounded

    19. Question 19. What Is The Important Aspect Of A Real-time System Or Mission Critical Systems?

      Answer :

      A real time operating system has well defined fixed time constraints. Process must be done within the defined constraints or the system will fail. An example is the operating system for a flight control computer or an advanced jet airplane. Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. Real-Time systems may be either hard or soft real-time.

      Hard real-time: Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM), Conflicts with time-sharing systems, not supported by general-purpose operating systems.

      Soft real-time: Limited utility in industrial control of robotics, Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

    20. Question 20. What Is Throughput, Turnaround Time, Waiting Time And Response Time?

      Answer :

      • Throughput : number of processes that complete their execution per time unit.
      • Turnaround time : amount of time to execute a particular process.
      • Waiting time : amount of time a process has been waiting in the ready queue.
      • Response time: amount of time it takes from when a request was submitted until the first response is produced, not output (for time-sharing environment).

    21. Question 21. What Resources Are Used When A Thread Created? How Do They Differ From Those When A Process Is Created?

      Answer :

      When a thread is created the threads does not require any new resources to execute the thread shares the resources like memory of the process to which they belong to. The benefit of code sharing is that it allows an application to have several different threads of activity all within the same address space. Whereas if a new process creation is very heavyweight because it always requires new address space to be created and even if they share the memory then the inter process communication is expensive when compared to the communication between the threads.

    22. Question 22. What Is Virtual Memory?

      Answer :

      Virtual memory is hardware technique where the system appears to have more memory that it actually does. This is done by time-sharing, the physical memory and storage parts of the memory one disk when they are not actively being used.

    23. Question 23. Why Paging Is Used?

      Answer :

      Paging is solution to external fragmentation problem which is to permit the logical address space of a process to be noncontiguous, thus allowing a process to be allocating physical memory wherever the latter is available.

    24. Question 24. How Did You Find Initial Support For A New Distro?

      Answer :

      The support from the community was awesome! As one of the first real Desktop oriented FreeBSD systems on the market, there was a ton of interest.

    25. Question 25. You Are Told That The Permissions Of A File Are 645. Quick, How Do You Calculate What It Means?

      Answer :

      The permissions value are always 4 for read, 2 for write, 1 for execute. The three numbers are always for owner, group, and everybody on the system. Therefore 645 means: owner - read and write, group - read only, everybody - read and execute. You'll rarely see such a permission set, but for interview question it might just work.

    26. Question 26. Explain The Difference Between Sighup, Sigusr1 And Sigusr2?

      Answer :

      Those are application specific and therefore are not defined on the OS level.

    27. Question 27. Explain The Difference Between Sigterm And Sigkill?

      Answer :

      SIGTERM asks the application to terminate in a polite way, it warns about the pending closure and asks the app to finish whatever it is doing. SIGKILL will kill the process no matter what. This is telling the application that it will be shut down no matter what.

    28. Question 28. How Do You Change Your Shell To Bash?

      Answer :

      % chsh -s /usr/local/bin/bash

    29. Question 29. What Is In The File /etc/ttys?

      Answer :

      Configuration for virtual consoles for the startup. By default FreeBSD has 8 virtual consoles.

    30. Question 30. Why Is/is Not Productx Included?

      Answer :

      People often ask why a particular product is or isn't included with OpenBSD. The answer is based on two things: the wishes of the developers and compatibility with the goals of the project. A product will not be included simply because it is "neat" -- it must also be "free" for use, distribution and modification by our standards. A product must also be stable and secure -- a bigger version number does not always mean a better product.

    31. Question 31. Is Openbsd Really Free?

      Answer :

      OpenBSD is all free. The binaries are free. The source is free. All parts of OpenBSD have reasonable copyright terms permitting free redistribution. This includes the ability to REUSE most parts of the OpenBSD source tree, either for personal or commercial purposes. OpenBSD includes NO further restrictions other than those implied by the original BSD license. Software which is written under stricter licenses cannot be included in the regular distribution of OpenBSD.

    32. Question 32. What Is New In Openbsd 4.3?

      Answer :

      The complete list of changes made to OpenBSD 4.2 to create OpenBSD 4.3 can be found on plus43.html, and highlights on the OpenBSD 4.3 Information page, however here are a few changes the OpenBSD team anticipate will require or warrant some special note to people upgrading or installing OpenBSD 4.3 who are familiar with older versions.

    33. Question 33. Who Maintains Openbsd?

      Answer :

      OpenBSD is maintained by a development team spread across many different countries. The project is coordinated by Theo de Raadt, located in Canada.

    34. Question 34. Explain About The Paging Systems?

      Answer :

      Paging systems can be modeled by abstracting the page reference string from the program and using the same reference string with different algorithms. These models can be used to make some predictions about paging behavior. Attention to issues such as determining the working set, memory allocations, and page size are required.

    35. Question 35. Describe The Two Phases Of Two-phase Locking?

      Answer :

      In the first phase, the process tries to lock all the records it needs, one at a time. If it succeeds, it begins the second phase, performing its updates and releasing the locks. No real work is done in the first phase.

    36. Question 36. Describe About Checkpointing?

      Answer :

      Checkpointing a process means that its state is written to a file so that it can be restarted later. The checkpoint contains not only the memory image, but also the resource state, that is, which resources are currently assigned to the process. To be most effective, new checkpoints should not overwrite old ones but should be written to new files. Whole sequences of checkpoint files are accumulated due to the process getting executed.

    37. Question 37. Give A Case Situation Where A Scheduling Is Needed?

      Answer :

      When an interrupt occurs, a scheduling decision may be made. If the interrupt came from an I/O device that has now completed its work, some process that was blocked waiting for the I/O may now be ready to run. It is up to the scheduler to decide if the newly ready process should run or not.

    38. Question 38. Describe About Preemptive Scheduling Algorithm?

      Answer :

      A preemptive scheduling algorithm picks a process and lets it run for a maximum of some fixed time. If it is still running at the end of the time interval, it is suspended and the scheduler picks another process to run. Doing preemptive scheduling requires having a clock interrupt occur at the end of the time interval to give control of the CPU back to the scheduler.

    39. Question 39. Give An Example Of Page Replacement In The Areas Of Computer Design?

      Answer :

      Majority of the computers have more than one memory caches consisting of 32-byte or 64-byte blocks of memory. Whenever a cache is full then some part of the block should be chosen for removal. This problem is precisely the same page replacement except on a shorter time scale.

    40. Question 40. Describe The Mechanism Of Upcall?

      Answer :

      When the kernel knows that a thread has blocked, the kernel notifies the processes run time system, passing as parameters on the stack the number of the thread in question and a description of the event that occurred. The notification happens by having the kernel activate the run-time system at a known starting address, roughly analogous to a signal in UNIX.

    41. Question 41. Describe About Threads?

      Answer :

      Different threads in a process are not quite as independent as different process. All threads share the same global variables as they have the same address space. One thread can read, write, or even completely wipe out another threads stack.

    42. Question 42. Describe About Multics?

      Answer :

      MULTICS is described as having a series of concentric rings, with the inner ones being more privileged than the outer ones. When a procedure in an outer ring wanted to call a procedure in an inner ring, it had to make the equivalent of a system call which is a TRAP instruction. MULTICS hardware made it possible to designate individual process as protected against reading, writing, or executing.

    43. Question 43. What Are Server Operating Systems?

      Answer :

      These run on servers, which are very large personal computers, work stations, or even mainframes. They serve multiple users at once over a network and allow the users to share hardware and software resources. Server O.S. provide various functions such as file and print service, or web service. Typical server operating systems are UNIX and Windows 2000.

    44. Question 44. Describe System Calls For File Management?

      Answer :

      To make changes a file must be opened. This call specifies the file name to be opened, either as an absolute path name or relative to the working directory, and a code of O_RDONLY, O_WRONLY or O_RDWR, meaning open for reading, writing or both. The file descriptor can then be used for reading or writing.

    45. Question 45. When Blue Screen Error Will Occur In Computer?

      Answer :

      It is an error screen displayed by certain operating systems, most notably Microsoft Windows, after encountering a critical system error. Bluescreens can be caused by poorly written device drivers, faulty memory, a corrupt Registry, or incompatible DLLs

       

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