What is a zombie?

Unix Interview Questions

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20. What is a zombie?

When a program forks and the child finishes before the parent, the kernel still keeps some of its information about the child in case the parent might need it - for example, the parent may need to check the child's exit status. 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.)

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Other Interview Questions

• How are devices represented in UNIX?
• What is 'inode'?
• Brief about the directory representation in UNIX
• What are the Unix system calls for I/O?
• How do you change File Access Permissions?
• What are links and symbolic links in UNIX file system?
• What is a FIFO?
• How do you create special files like named pipes and device files?
• Discuss the mount and unmount system calls
• How does the inode map to data block of a file?
• What is a shell?
• Brief about the initial process sequence while the system boots up.
• What are various IDs associated with a process?
• Explain fork() system call.
• Predict the output of the following program code
• Predict the output of the following program code
• List the system calls used for process management:
• How can you get/set an environment variable from a program?:
• How can a parent and child process communicate?
• What is a zombie?
• What are the process states in Unix?
• What Happens when you execute a program?
• What Happens when you execute a command?
• What is a Daemon?
• What is 'ps' command for?
• How would you kill a process?
• What is an advantage of executing a process in background?
• How do you execute one program from within another?
• What is IPC? What are the various schemes available?
• What is the difference between Swapping and Paging?
• What is major difference between the Historic Unix and the new BSD release of Unix System V in terms of Memory Management?
• What is the main goal of the Memory Management?
• What is a Map?
• What scheme does the Kernel in Unix System V follow while choosing a swap device among the multiple swap devices?
• What is a Region?
• What are the events done by the Kernel after a process is being swapped out from the main memory?
• Is the Process before and after the swap are the same? Give reason.
• What do you mean by u-area (user area) or u-block?
• What are the entities that are swapped out of the main memory while swapping the process out of the main memory?
• What is Fork swap?
• What is Expansion swap?
• How the Swapper works?
• What are the processes that are not bothered by the swapper? Give Reason.
• What are the requirements for a swapper to work?
• What are the criteria for choosing a process for swapping into memory from the swap device?
• What are the criteria for choosing a process for swapping out of the memory to the swap device?
• What do you mean by nice value?
• What are conditions on which deadlock can occur while swapping the processes?
• What are conditions for a machine to support Demand Paging?
• What is ‘the principle of locality’?
• What is the working set of a process?
• What is the window of the working set of a process?
• What is called a page fault?
• What are data structures that are used for Demand Paging?
• What are the bits that support the demand paging?
• How the Kernel handles the fork() system call in traditional Unix and in the System V Unix, while swapping?
• Difference between the fork() and vfork() system call?
• What is BSS(Block Started by Symbol)?
• What is Page-Stealer process?
• Name two paging states for a page in memory?
• What are the phases of swapping a page from the memory?
• What is page fault? Its types?
• In what way the Fault Handlers and the Interrupt handlers are different?
• What is validity fault?
• What does the swapping system do if it identifies the illegal page for swapping?
• What are states that the page can be in, after causing a page fault?
• In what way the validity fault handler concludes?
• At what mode the fault handler executes?
• What do you mean by the protection fault?
• How the Kernel handles the copy on write bit of a page, when the bit is set?
• For which kind of fault the page is checked first?
• In what way the protection fault handler concludes?
• How the Kernel handles both the page stealer and the fault handler?
• Explain different types of Unix systems.
• 73. Explain kernal and shell.
• 74. What is ex and vi ?
• Which are typical system directories below the root directory?
• Construct pipes to execute the following jobs.
• Explain the following commands.
• What is the significance of the “tee” command?
• What does the command “ $who | sort –logfile > newfile” do?
• What does the command “$ls | wc –l > file1” do?
• Which of the following commands is not a filter man , (b) cat , (c) pg , (d) head
• How is the command “$cat file2 “ different from “$cat >file2 and >> redirection operators ?
• Explain the steps that a shell follows while processing a command.
• What difference between cmp and diff commands?
• What is the use of ‘grep’ command?
• What is the difference between cat and more command?
• Write a command to kill the last background job?
• Which command is used to delete all files in the current directory and all its sub-directories?
• Write a command to display a file’s contents in various formats?
• What will the following command do?
• Is it possible to create new a file system in UNIX?
• Is it possible to restrict incoming message?
• What is the use of the command "ls -x chapter[1-5]"
• Is ‘du’ a command? If so, what is its use?
• Is it possible to count number char, line in a file; if so, How?
• Name the data structure used to maintain file identification?
• How many prompts are available in a UNIX system?
• How does the kernel differentiate device files and ordinary files?
• How to switch to a super user status to gain privileges?
• What are shell variables?
• What is redirection?
• How to terminate a process which is running and the specialty on command kill 0?
• What is a pipe and give an example?
• Explain kill() and its possible return values.