1. Tell the differences between Unix and Linux. Then please list some operating systems (at least three) which belong to Unix but not Linux.

2. What is the pipe mechanism in UNIX? And show one command using pipe and explain how the pipe works in it?

3. What does GNU stand for? What is the GNU project? Which organization funded the development of GNU project?

4. In class, you have learned the meaning of read, write and execute permission for regular file. However, these permissions are also applied to directories. So please describe the meaning of read, write, and execute permission for directory.