Frequently- asked Basic UNIX Interview Questions With Answers – Download PDF file. Frequently- asked Basic UNIX Interview Questions With Answers – Download PDF file. Also you can Download this “UNIX Interview Questions With Answers” as a PDF file. The execlp call overlays the existing program with the new one , runs that and exits. The original program gets back control only when an error occurs. What are the various schemes available? The term IPC (Inter- Process Communication) describes various ways by which different process running on some operating system communicate between each other. Various schemes available are as follows: Pipes: One- way communication scheme through which different process can communicate. The problem is that the two processes should have a common ancestor (parent- child relationship). However this problem was fixed with the introduction of named- pipes (FIFO). Message Queues : Message queues can be used between related and unrelated processes running on a machine. Over the past three weeks, I’ve been asked by a number of administrators in the international world for a list of skills and questions for interviewing potential. Best Study Guide is exam questions and answers certification fees 2015 practice labs. Ccna are exam questions download. Basics - 135 Basics interview questions and 709 answers by expert members with experience in Basics subject. Discuss each question in detail for better understanding. SAS Certified Base Programmer Certification Questions and Online Practice Exam for A00-211 Certification Exams. Latest sample questions and free demo exams included. Business intelligence Interview Questions and Answers will guide all of us here that Business intelligence (BI) refers to all the skills, technologies, applications. Hi, Thanks for visiting my blog. The basic of C and SAS programming is same like loop, conditional statement but still its a programming language from. Shared Memory: This is the fastest of all IPC schemes. The memory to be shared is mapped into the address space of the processes (that are sharing). The speed achieved is attributed to the fact that there is no kernel involvement. But this scheme needs synchronization. Various forms of synchronisation are mutexes, condition- variables, read- write locks, record- locks, and semaphores. Process size must be less than or equal to the available main memory. Sunbelt Midwest, with 4 offices in Minneapolis, Chicago and Milwaukee, has a trusted team of business brokers to help you buy or sell your business at the highest. MetaPack are the leading provider of delivery management technology to enterprise retailers and retail delivery partners across the world. Our platform integrates to. Learn about new USPSTF latent TB infection recommendation. Like CDC TB’s new Facebook page. See newly released TB Treatment Guidelines. See the Take on Latent. Avaya Certification is ip office configuration and maintenance exam 3001 jobs. Certification Path are 4000 ip office basic. It is easier to implementation and overhead to the system. Swapping systems does not handle the memory more flexibly as compared to the paging systems. Paging: Only the required memory pages are moved to main memory from the swap device for execution. Process size does not matter. Gives the concept of the virtual memory. It provides greater flexibility in mapping the virtual address space into the physical memory of the machine. Allows more number of processes to fit in the main memory simultaneously. Allows the greater process size than the available physical memory. Demand paging systems handle the memory more flexibly. Historic Unix uses one Swap Device and Unix System V allow multiple Swap Devices. Fault handlers sleep in the context of the process that caused the memory fault. The fault refers to the running process and no arbitrary processes are put to sleep. This happens when the swapping system identifies any invalid memory reference. A process also incur the protection fault when it attempts to write a page whose copy on write bit was set during the fork() system call. After copying the Kernel updates the page table entry with the new page number. Then Kernel decrements the reference count of the old pfdata table entry. In cases like, where the copy on write bit is set and no processes are sharing the page, the Kernel allows the physical page to be reused by the processes. By doing so, it clears the copy on write bit and disassociates the page from its disk copy (if one exists), because other process may share the disk copy. Then it removes the pfdata table entry from the page- queue as the new copy of the virtual page is not on the swap device. It decrements the swap- use count for the page and if count drops to 0, frees the swap space. Kernel handles the validity fault and the process will incur the protection fault if any one is present. It recalculates the process- priority and checks for signals. If the sum of the working sets of all processes is greater that the physical memory then the fault handler will usually sleep because it cannot allocate pages for a process. This results in the reduction of the system throughput because Kernel spends too much time in overhead, rearranging the memory in the frantic pace. And on a page fault the kernel updates the working set by reading the page from the secondary device. They are,– Page table entries,– Disk block descriptors,– Page frame data table (pfdata),– Swap- use table. Thus, device files and other files are named and accessed in the same way. The inode contains info about the file- size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode. In addition to descriptions about the file, the inode contains pointers to the data blocks of the file. If the file is large, inode has indirect pointer to a block of pointers to additional data blocks (this further aggregates for larger files). A block is typically 8k. Inode consists of the following fields: – File owner identifier– File type– File access permissions– File access times– Number of links– File size– Location of the file data. A directory is a special file that the kernel maintains. Only kernel modifies directories, but processes can read directories. The contents of a directory are a list of filename and inode number pairs. When new directories are created, kernel makes two entries named . Links can be used to assign more than one name to a file, but cannot be used to assign a directory more than one name or link filenames on different computers. Symbolic link . One of the most obvious is that the parent can get the exit status of the child. To be able to get this information, the parent calls `wait()’; In the interval between the child terminating and the parent calling `wait()’, the child is said to be a `zombie’ (If you do `ps’, the child will have a `Z’ in its status field to indicate this.)3. Unix processes have the following states: Running : The process is either running or it is ready to run . Waiting : The process is waiting for an event or for a resource. Stopped : The process has been stopped, usually by receiving a signal. Zombie : The process is dead but have not been removed from the process table. This environment contains everything needed for the system to run the program as if no other program were running on the system. Each process has process context, which is everything that is unique about the state of the program you are currently running. Every time you execute a program the UNIX system does a fork, which performs a series of operations to create a process context and then execute your program in that context. The steps include the following: – Allocate a slot in the process table, a list of currently running programs kept by UNIX.– Assign a unique process identifier (PID) to the process.– i. Copy the context of the parent, the process that requested the spawning of the new process.– Return the new PID to the parent process. This enables the parent process to examine or control the process directly. After the fork is complete, UNIX runs your program. This creates a new process that the shell will use to run the ls program. The shell has UNIX perform an exec of the ls program. This replaces the shell program and data with the program and data for ls and then starts running that new program. The ls program is loaded into the new process context, replacing the text and data of the shell. The ls program performs its task, listing the contents of the current directory. It can also be defined as the background process that does not belong to a terminal session. Many system functions are commonly performed by daemons, including the sendmail daemon, which handles mail, and the NNTP daemon, which handles USENET news. Many other daemons may exist. Some of the most common daemons are: – init: Takes over the basic running of the system when the kernel has finished the boot process.– inetd: Responsible for starting network services that do not have their own stand- alone daemons. For example, inetd usually takes care of incoming rlogin, telnet, and ftp connections.– cron: Responsible for running repetitive tasks on a regular schedule. The information given are the process identification number (PID),the amount of time that the process has taken to execute so far etc. The PID of a process can be got using . At the end of the command you add the special background symbol, &. This symbol tells your shell to execute the given command in the background. Example: cp *.* ./backup& (cp is for copy)4. Regions are sharable among the process. If the reference count becomes zero, swaps the region out of the main memory,– Kernel allocates the space for the swapping process in the swap device,– Kernel locks the other swapping process while the current swapping operation is going on,– The Kernel saves the swap address of the region in the region table. Give reason. Process before swapping is residing in the primary memory in its original form. The regions (text, data and stack) may not be occupied fully by the process, there may be few empty slots in any of the regions and while swapping Kernel do not bother about the empty slots while swapping the process out. After swapping the process resides in the swap (secondary memory) device. The regions swapped out will be present but only the occupied region slots but not the empty slots that were present before assigning. While swapping the process once again into the main memory, the Kernel referring to the Process Memory Map, it assigns the main memory accordingly taking care of the empty slots in the regions. This is local to the Process, i. When the parent process calls fork() system call, the child process is created and if there is short of memory then the child process is sent to the read- to- run state in the swap device, and return to the user state without swapping the parent process. When the memory will be available the child process will be swapped into the main memory. To do this Kernel reserves enough space in the swap device. Then the address translation mapping is adjusted for the new virtual address space but the physical memory is not allocated. At last Kernel swaps the process into the assigned space in the swap device. The Swapper operates only in the Kernel mode and it does not uses System calls instead it uses internal Kernel functions for swapping. It is the archetype of all kernel process.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
January 2017
Categories |