Operating System-Unix [3i Infotech Placement]: Sample Questions 26 - 28 of 78

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Question 26

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Describe in Detail

Essay▾

What is a zombie?

Explanation

  • Process that has completed execution but still retains entry in the process table.
  • At end of the process, every memory resource is deallocated and can be used by other processes, however, entry of the process remains unavailable.
  • When exit status of a child is read by the parent using the wait system call- zombie can be removed.
  • Ones the zombie is removed, the process id in the process table is removed and reused.
  • Zombie state finishes when the parent dies.
  • Zombie processes accumulate in the system when parent process is not programmed properly and never calls wait () -zombine children remain in the memory.

Question 27

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Describe in Detail

Essay▾

What are the criteria for choosing a process for swapping out of the memory to the swap device?

Explanation

Swapping Process Out
  • The kernel gathers the page addresses of data at primary memory to be swapped out.
  • Kernel copies the physical memory assigned to a process to the space allocated on the swap device.
  • The mapping between physical memory and swap device is kept in page table entry.

Question 28

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Describe in Detail

Essay▾

What are links and symbolic links in UNIX file system?

Explanation

Define Symbolic Links
  • A link is a pointer or reference to another file.
  • A directory UNIX has a list of file names and corresponding inodes.
  • Link points to another file.

Hard Link

  • In hard link- the i-numbers of two difference directory file entries point to the same inode.

Soft Link

  • A symbolic link or a soft link a special type of link containing links or references to another file or directory in the form of the path.
  • To create a symbolic link, following command is used:

    Ln-s target link_name

  • Path is the target and name of the link is link_name.
  • Symbolic link can created to creare a file system based on different views of the user.

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