Контрольная Работа по Операционным Системам (2026)

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

   typedef struct {
     unsigned int size;
     union {
       char *s;
       short i;
       int n;
     } u;
   } Var;
   

   Answer: 16

2. What will be the result of sizeof(p) for the code snippet below?

   char s[] = "Hello!";
   int *p = s;
   

   Answer: 8

3. You have the following small program. What value will be retuned by the main function if the program is compiled with this command gcc prog.c -DSUCCESS -o prog?

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

   Answer: 0

4. You have a project that uses static libraries: libfred.a, libjohn.a, and libmike.a. Library libfred.a has no dependencies, library libjohn.a depends on library libmike.a. Which commands will lead to linking errors?

   • A. gcc -o main main.o -L. -lfred -ljohn -lmike
   • B. gcc -o main main.o -L. -lfred -lmike -ljohn
   • C. gcc -o main main.o -L. -ljohn -lmike -lfred
   • D. gcc -o main main.o -L. -ljohn -lfred -lmike
   • E. gcc -o main main.o -L. -lmike -lfred -ljohn
   • F. gcc -o main main.o -L. -lmike -ljohn -lfred

   Answer: B, E and F

5. What of the following global variables and functions are considered weak 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: A and F

   Note: The question is not well-formulated. The correct answer should be “None”. So, the following answers are accepted: None (in any form) + A and/or F.

6. Write a declaration of variable p, which is a pointer to a function that:
   • has 1st parameter which is a constant C string (pointer to char);
   • has 2nd parameter which is a non-negative integer;
   • returns a C string (pointer to char).

   Answer: char* (*p)(const char*, unsigned int)

   Notes: Spaces and semicolon are not important here. Some answers were marked as invalid because of this, it will be fixed.

7. You have a malloc library based on an implicit list. The size of header/footer is 4 bytes and payload is 4-byte aligned. You call malloc with size: 1, 2, 3, 4, and 5 bytes. How many bytes are wasted on internal fragmentation?

   Answer: 49

8. What system call is used to map a file into memory (type just its name without parameters)?

   Answer: mmap

9. See the program below. Which variable is not guaranteed to have final value 50000?

   std::atomic<int> a = 0;
   thread_local int b = 0;
   int c = 0;
   std::mutex m;
   
   void increment() {
     for (int i = 0; i < 10000; ++i) {
       a++;
       {
         std::lock_guard<std::mutex> g(m);
         b++;
         c++;
       }
     }
   }
   
   int main() {
     std::vector<std::thread> threads;
     for (int i = 0; i < 5; ++i)
       threads.push_back(std::thread(increment));
     for (int i = 0; i < 5; ++i)
       threads[i].join();
     return 0;
   }
   

   • A. a
   • B. b
   • C. c

   Answer: B and C

10. What number will be printed by the parent process if the child 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: 3

11. What will be printed by the following code for a file with contents abcde?

    int fd1;
    char c1, c2;
    char *fname = argv[1];
    fd1 = open(fname, O_RDONLY, 0);
    read(fd1, &c1, 1);
    if (fork()) {
      wait(NULL);
      read(fd1, &c2, 1);
    } else {
      read(fd1, &c2, 1);
    }
    printf("%c%c", c1, c2);
    

    Answer: abac

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

    Answer: ln myfile mylink

13. Write a permission mask to give all permissions (read/write/execute) to user and nothing to anyone else. It looks like abc, where a/b/c are integer numbers.

    Answer: 700

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

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

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

    Answer: B

15. From which directory is user ejudge not allowed to delete a file?

    drwxrwxrwx 2 tatarnikov tatarnikov 4096 Jun 15 22:19 dir1
    drwxrwxr-x 2 tatarnikov ejudge     4096 Jun 15 22:19 dir2
    drwxrwxr-t 2 tatarnikov ejudge     4096 Jun 15 22:14 dir3
    drwxrwxr-x 2 ejudge     ejudge     4096 Jun 15 22:19 dir4
    

    • A. dir1
    • B. dir2
    • C. dir3
    • D. dir4

    Answer: C