Top Linux OS Management Interview Questions & Answers:

1. For the below mentioned code:

int main() {
int fd;
fd = open("logfile", O_CREAT|O_RDWR, 0600);
lseek(fd, 5, SEEK_CUR);
write(fd, "Hello", 5);
return 0;
}

What is the logfile size now if it's initially was 1024 bytes?

a) 5
b) 1024
c) 1029
d) 1034

b) 1024

2. Code snippets

str1="45678n"
str2="123n"
f1 = fopen(file1,RDWR,RWX)
f2 = dup(f1)
write(f1,str1,len_str1)
write(f2,str2,len_str2)

o/p:

a) 12378
b) 123(newline)8(newline)
c) 123(newline)78(newline)
d) 45678(newline)123(newline)

d) 45678(newline)123(newline)

3. Code snippet (file1 size is 2024)

f1 = fopen (file1, RDWR, RWX)
lseek(f1,1024,SEEK_SET)
write(f1,buf,10)
What is offset now.

a) 1024
b) 1034
c) 2034
d) 2054

b) 1034

4. Code snippets

str1="45678n"
str2="123n"
f1 = fopen(file1,RDWR,RWX)
f2 = fopen(file1,RDWR,RWX)
write(f1,str1,len_str1)
write(f2,str2,len_str2)

o/p:

a) 12378
b) 123(newline)8(newline)
c) 123(newline)78(newline)
d) 45678(newline)123(newline)

b) 123(newline)8(newline)

5. What is stored in logfile as per below mentioned code if we execute ./a.out > logfile?

int main() {
int fd;
close(1);
fd = open("logfile",O_RDWR, 0744);
write(fd, "Hello", 5);
printf("Worldn");
return 0;
}

a) Hello
b) HelloWorld
c) World
d) None

b) HelloWorld

6. Given a code snippet below?

#define PERMS (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH)
int main() {
int fd1, fd2;
umask(0);
fd1 = open("file1", O_CREAT | O_RDWR, PERMS)
umask(S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
fd2 = open("file2", O_CREAT | O_RDWR, PERMS)
return 0;
}

The newly created files file1 and file2 will have the permissions respectively
a) rw-rw-rw- r---
b) r--- rw-rw-rw-
c) rw-rw-rw- rw---
d) None of the above

c) rw-rw-rw- rw---

7. Below is the code:

int main() {
int fd1, fd2;
struct stat buff1, buff2;
fd1 = open("1.txt", O_RDWR);
fd2 = open("2.txt", O_RDWR | O_APPEND);
lseek(fd1, 10000, SEEK_SET);
write(fd1, "abcdefghij", 10);
write(fd2, "abcdefghij", 10);
fstat(fd1, &buff1);
fstat(fd2, &buff2);
printf(" %d %d", buff1.st_size, buff2.st_size);
return 0;
}

Before running the program, the file 1.txt and 2.txt size is 20 each. What is the output?
a) 30 30
b) 100020 20
c) 100030 30
d) 100010 30

d) 100010 30

8. Which function can be used instead of the dup2 to duplicate the file descriptor?
a) read()
b) open()
c) stat()
d) fcntl()

d) fcntl()

9. If one of the thread in multi-threaded process is blocked on an I/O, which of the following is true?
a) The entire process with block if their is no kernel supported threads
b) Other threads of the process will continue to execute even if there is no kernel supported threads
c) It depends on specific implementatation
d) All of the above

a) The entire process with block if their is no kernel supported threads

10. If the fork() system call returns -1, then it means?
a) No new child process is created
b) The child process is an orphan
c) The child process is in Zombie

a) No new child process is created

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11. dup2(1,0):
a) closes the stdout and copies the stdin descriptor to stdout
b) closes the stdin and copies the stdout descriptor to stdin
c) will produce compilation error
d) None of the above

b) closes the stdin and copies the stdout descriptor to stdin

12. namei() is:
a) ANSI C library function
b) C library function
c) System call
d) kernel routine

d) kernel routine

13. Which system call is used to create a hard link?
a) hard-link
b) link
c) symlink
d) ln

b) link

14. read() system call on success returns:
a) 0
b) -1
c) number of character
d) none

c) number of character

15. Printf() uses which system call:
a) open
b) read
c) write
d) close

c) write

16. The file system information is stored in:
a) Boot block
b) Super Block
c) Inode Table
d) Data Block

b) Super Block

17. What is the use of fcntl function?
a) locking a file
b) reading the file descriptor flag
c) changing the file status flag
d) all the above

d) all the above

18. Switch table is used by:
a) device special file
b) directory file
c) fifo
d) link file.

a) device special file

19. What is the default number of files open per user process?
a) 0
b) 1
c) 2
d) 3

d) 3

20. File descriptor table indexes which kernel structure?
a) struct file
b) strruct fs_struct
c) files_struct
d) struct inode

a) struct file

21. Each process has unique:
a) fd table
b) file table
c) inode table
d) data block table

a) fd table

22. Which one can be a real time schedule policy?
a) SCHED_FIFO
b) SCHED_SPF
c) SCHED_OTHER
d) SCHED_FILO

a) SCHED_FIFO

23. Among these files which has an ELF format:
a) shared objects
b) core
c) executables
d) all of the above

d) all of the above

24. Describe the use of strace command

Strace can be used to check the system calls called by the program. So, this can be used for debugging and benchmarking purposes.

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25. On x86-32 Linux, at which address the user stack resides normally?
a) 000000000
b) 0x3fff0000
c) 0x7fff0000
d) 0xbfff0000

d) 0xbfff0000

26. Is page table per process entity?
a) Yes
b) No

a) Yes

27. Which system call can be used by a user process to lock a memory so that it cannot be swapped out?

memlock()

28. Mm_struct maintains?
a) memory files
b) open files
c) pipe
d) active memory regions

d) active memory regions

29. LRU stands for:
a) Last received Unit
b) Least recently Used
c) Least recently usable
d) Lost Recoverd unit

b) Least recently Used

30. A system has 512MB of physical memory. Which among the following is not a suitable virtual memory size for this system architecture?
a) 512MB
b) 256M
c) 4GB
d) None of the above

d) None of the above

31. On x86-32 Linux, at which address the code segment of the program starts?
a) 000000000
b) 008048000
c) 080000000
d) 0xbfff0000

b) 008048000

32. Solaris real time class priority is:
a) 0-59
b) 60-99
c) 100-159
d) 160-169

c) 100-159

33. Solaris system class priority is:
a) 0-59
b) 60-99
c) 100-159
d) 160-169

b) 60-99

34. In Linux kernel-2.6 Real time priority ranges from:
a) 0 to 99
b) 0 to 139
c) -20 to 19
d) 100 to 139

a) 0 to 99

35. Nice can be used by an ordinary process to:
a) increase the priority of a process
b) decrease the priority of a process
c) increase or decrease the priority of a process

b) decrease the priority of a process