Unix Interview Questions & Answers
Showing 10 of 53 questions | Page 5
Unix technical interview questions and answers are frequently asked in system administration, DevOps, backend development, and support engineering roles. Unix forms the base for Linux and macOS, so companies expect candidates to understand file permissions, commands, shell scripting, process management, filters, pipes, and environment variables. Interviews in TCS, Infosys, Wipro, Cognizant, Capgemini, and Accenture often include Unix questions during both technical rounds and written tests. This guide explains frequently asked Unix commands and concepts using simple language, making it easy for freshers and experienced candidates to prepare. You can also download Unix interview questions PDFs and practice mock commands for better preparation.
Showing 10 of 53 questions
41. Difference between the fork() and vfork() system call?
During the fork() system call the Kernel makes a copy of the parent processs address space and attaches it to the child process.
But the vfork() system call do not makes any copy of the parents address space, so it is faster than the fork() system call. The child process as a result of the vfork() system call executes exec() system call. The child process from vfork() system call executes in the parents address space (this can overwrite the parents data and stack ) which suspends the paren
42. What is BSS(Block Started by Symbol)?
A data representation at the machine level, that has initial values when a program starts and tells about how much space the kernel allocates for the un-initialized data. Kernel initializes it to zero at run-time.
43. What is Page-Stealer process?
This is the Kernel process that makes rooms for the incoming pages, by swapping the memory pages that are not the part of the working set of a process. Page-Stealer is created by the Kernel at the system initialization and invokes it throughout the lifetime of the system. Kernel locks a region when a process faults on a page in the region, so that page stealer cannot steal the page, which is being faulted in.
44. Name two paging states for a page in memory?
The two paging states are:
The page is aging and is not yet eligible for swapping,
The page is eligible for swapping but not yet eligible for reassignment to other virtual address space.
45. What are the phases of swapping a page from the memory?
Page stealer finds the page eligible for swapping and places the page number in the list of pages to be swapped.
Kernel copies the page to a swap device when necessary and clears the valid bit in the page table entry, decrements the pfdata reference count, and places the pfdata table entry at the end of the free list if its reference count is 0.
46. In what way the Fault Handlers and the Interrupt handlers are different?
Fault handlers are also an interrupt handler with an exception that the interrupt handlers cannot sleep. 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.
47. What is validity fault?
If a process referring a page in the main memory whose valid bit is not set, it results in validity fault.
The valid bit is not set for those pages:
that are outside the virtual address space of a process,
that are the part of the virtual address space of the process but no physical address is assigned to it.
48. What does the swapping system do if it identifies the illegal page for swapping?
If the disk block descriptor does not contain any record of the faulted page, then this causes the attempted memory reference is invalid and the kernel sends a “Segmentation violation” signal to the offending process. This happens when the swapping system identifies any invalid memory reference.
49. At what mode the fault handler executes?
At the Kernel Mode.
50. What do you mean by the protection fault?
Protection fault refers to the process accessing the pages, which do not have the access permission. 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.