Operating Systems Midterm (2026)

1. Data type Rec is defined below. What will be returned by sizeof(Rec) (64-bit machine)?

   typedef struct {
     char a;
     short b;
     char c;
   } *Rec;
   

   Answer: 8

2. Data type Union is defined below. What will be returned by sizeof(Union) (64-bit machine)?

   typedef union {
     int x;
     float y;
     char z[5];
   } Union;
   

   Answer: 8

3. A pointer to an array called parr is defined below. What will be the result of sizeof(parr)/sizeof(parr[0]).

   int arr[10];
   int *parr = arr;
   

   Answer: 2

4. You have the following small program. What value will be retuned by the main function if the program is compiled with default flags?

   #ifdef SUCCESS
     #define RET 0
   #else
     #define RET 1
   #endif
   
   int main() {
     return RET;
   }
   

   Answer: 1

5. What of the following global variables and functions are considered strong symbols by the linker?

   • A. void func();
   • B. void func() {}
   • C. static void func() {}
   • D. int x = 10;
   • E. static int x = 10;
   • F. extern int x;

   Answer: B and D

6. Write a declaration of variable p, which is a pointer to a function that returns int and has one parameter of type int.

   Answer: int (*p)(int)

7. Which is the slowest way of memory allocation?

   • A. Stack memory
   • B. Heap memory
   • C. Static memory

   Answer: B

8. What utility and system call is used to send a signal?

   Answer: kill

9. What of the following signals cannot be handled in a user program?

   • A. INT
   • B. STOP
   • C. CONT

   Answer: B and C

10. What number will be printed by a child process if it is successfully created?

    int main() {
      pid_t pid;
      pid = fork();
      if (pid < 0) {
        printf("1");
      } else if (pid == 0) {
        printf("2");
      } else {
        printf("3");
      }
      return 0;
    }
    

    Answer: 2

11. What will be printed by the following code?

    int fd1, fd2, fd3;
    char c1, c2, c3;
    char *fname = argv[1];
    fd1 = open(fname, O_RDONLY, 0);
    fd2 = open(fname, O_RDONLY, 0);
    fd3 = open(fname, O_RDONLY, 0);
    dup2(fd2, fd3);
    read(fd1, &c1, 1);
    read(fd2, &c2, 1);
    read(fd3, &c3, 1);
    printf("%c %c %c\n", c1, c2, c3);
    

    Answer: a a b

12. Write a command that will create a symbolic link called mylink for file called myfile.

    Answer: ln -s myfile mylink

13. Write a permission mask to give all rights to everyone (read/write/execute permissions to user/group/other). It looks like abc, where a/b/c are integer numbers.

    Answer: 777

14. Which file is the same as file file1.txt?

    35153094 -rw-rw-r-- 2 andrewt andrewt 9 Jun  3 18:08 file1.txt
    35153285 -rw-rw-r-- 1 andrewt andrewt 9 Jun  3 18:08 file2.txt
    35140410 lrwxrwxrwx 1 andrewt andrewt 9 Jun  3 18:07 file3.txt -> file1.txt
    35153094 -rw-rw-r-- 2 andrewt andrewt 9 Jun  3 18:08 file4.txt
    

    • A. file2
    • B. file3
    • C. file4

    Answer: C