Operating Systems 2015F: Assignment 3

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

1. 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
2. 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
3. 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
4. Which of the following is a character/stream device?
   • Hard Disk drive
   • Sound card (audio device)
   • DVD drive
   • All of the above
5. 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 did you overwrite?
   • Data blocks
   • inodes
   • directory blocks
   • All of the above
6. 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.
7. Without errors, what does the fork system call return?
   1. the child’s process ID
   2. 0
   3. Both (a) and (b)
   4. None of the above.

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

Standard C library routines such as printf are available in the kernel. true or false

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 program?

• The process is multithreaded
• The dynamic linker is broken
• The process is running as root
• The process was statically linked