Operating Systems 2015F: Assignment 3

Please answer the following questions on cuLearn by 8 PM on Tuesday, October 6th.

1. Standard C library routines such as printf are available in the kernel. True or False
2. Without errors, what does the fork system call return?
   • the child’s process ID
   • 0
   • Both (a) and (b)
   • None of the above.
3. What is something that userspace programs can do easily that is difficult to do from kernel code?
   • Open a file
   • Display text on the screen
   • Send data over a socket
   • All of the above
4. System calls are used to access the kernel because...
   • The kernel runs in a separate process
   • function calls are too slow
   • processes cannot see kernel memory
   • All of the above
5. You can create a new process running an executable by...
   • making an execve system call
   • making a fork system call
   • Both A and B
   • None of the above
6. Which of the following is normally assigned character/stream device on UNIX-like systems?
   • Hard Disk drive
   • Sound card (audio device)
   • DVD drive
   • All of the above
7. If a process makes many system calls (as seen by strace) but produces no library calls (as seen by ltrace), what is a reasonable assumption regarding the process and the program it is running?
   • The program is multithreaded
   • The dynamic linker is broken
   • The process is running as root
   • The program was statically linked
8. If a process creates many child processes then changes an environment variable X...
   • X is also changed in its parent process
   • X is changed in all child processes
   • Wait, a process cannot change its environment variables
   • None of the above
9. In playing around with the dd command in /dev you accidentally overwrote a small part of a USB drive formatted with an ext4 filesystem. You run fsck and repair the filesystem. No files have been corrupted; however, you find a directory that had a few files is now empty, and its files have now appeared /lost+found but with seemingly random numeric filenames (like #5123). What part of the filesystem do you know you overwrote?
   • data blocks
   • inode blocks
   • directory blocks
   • All of the above
10. There is a directory called /mydisk, and in this directory there are three files, A, B, and C. You run the command "mount /dev/sdb1 /mydisk"; afterwards you see that /mydisk contains the file B along with a directory lost+found. We see the file B but not the files A and C because...
    • A, B, and C still exist but are now hidden; the file B that we see is a different file that just happens to have the same filename B.
    • A and C got randomly erased by the mount command but B was left alone.
    • lost+found contains the old A, B, and C
    • None of the above.

Solutions

1. Standard C library routines such as printf are available in the kernel. False
2. Without errors, what does the fork system call return?
   • the child’s process ID
   • 0
   • Both (a) and (b)
   • None of the above.
3. What is something that userspace programs can do easily that is difficult to do from kernel code?
   • Open a file
   • Display text on the screen
   • Send data over a socket
   • All of the above
4. System calls are used to access the kernel because...
   • The kernel runs in a separate process
   • function calls are too slow
   • processes cannot see kernel memory
   • All of the above
5. You can create a new process running an executable by...
   • making an execve system call
   • making a fork system call
   • Both A and B
   • None of the above
6. Which of the following is normally assigned character/stream device on UNIX-like systems?
   • Hard Disk drive
   • Sound card (audio device)
   • DVD drive
   • All of the above
7. If a process makes many system calls (as seen by strace) but produces no library calls (as seen by ltrace), what is a reasonable assumption regarding the process and the program it is running?
   • The program is multithreaded
   • The dynamic linker is broken
   • The process is running as root
   • The program was statically linked
8. If a process creates many child processes then changes an environment variable X...
   • X is also changed in its parent process
   • X is changed in all child processes
   • Wait, a process cannot change its environment variables
   • None of the above
9. In playing around with the dd command in /dev you accidentally overwrote a small part of a USB drive formatted with an ext4 filesystem. You run fsck and repair the filesystem. No files have been corrupted; however, you find a directory that had a few files is now empty, and its files have now appeared /lost+found but with seemingly random numeric filenames (like #5123). What part of the filesystem do you know you overwrote?
   • data blocks
   • inode blocks
   • directory blocks
   • All of the above
10. There is a directory called /mydisk, and in this directory there are three files, A, B, and C. You run the command "mount /dev/sdb1 /mydisk"; afterwards you see that /mydisk contains the file B along with a directory lost+found. We see the file B but not the files A and C because...
    • A, B, and C still exist but are now hidden; the file B that we see is a different file that just happens to have the same filename B.
    • A and C got randomly erased by the mount command but B was left alone.
    • lost+found contains the old A, B, and C
    • None of the above.