Question 1 :
Is it possible to restrict incoming message?
Yes, using the 'mesg' command.
Question 2 :
What is the use of the command "ls -x chapter[1-5]"
ls stands for list; so it displays the list of the files that starts with 'chapter' with suffix '1' to '5', chapter1, chapter2, and so on.
Question 3 :
Is 'du' a command? If so, what is its use?
Yes, it stands for 'disk usage'. With the help of this command you can find the disk capacity and free space of the disk.
Question 4 :
Is it possible to count number char, line in a file; if so, How?
Yes, wc-stands for word count.
wc -c for counting number of characters in a file.
wc -l for counting lines in a file.
Question 5 :
Name the data structure used to maintain file identification?
'inode', each file has a separate inode and a unique inode number.