1. Why is UNIX more portable than other operating system?Ans. UNIX is an operating system which is readily available, searchable and has complete documentation both on the system and online via the internet. Changes can easily do on this operating system. Taking an example, when C programming language was developed, the UNIX operating system itself was rewritten into C. This enabled UNIX to become the more open portable than other operating system today.2. Explain briefly the significance of a UNIX file system?Ans. The significance of a UNIX file system can be explained as:

a. It has excellent use and control of system resources.b. It has very high reliability (long uptimes between reboots).c. It is readily available, searchable, and has complete

documentation both on the system and online via the internet.

d. Massive stores of free software available for downloading and building.

e. It is able to interact with more than one user at a time.

3. Distinguish between internal and external commands with examples.

Ans. Some commands in UNIX are internal, built into the shell. For example, the cd command is built-in. That is, the shell interprets the command and changes the current directory. On the other hand, cat command is an external program stored in the file /bin/cat, which is used to make files.

The shell doesn’t start a separate process to run internal commands. External commands require the shell to run a new subprocess; this takes some time, especially if the system is busy.

4. Explain the output of the ls –l command.Ans. The command ls –l lists seven attributes of all the files in the working directory. The top list gives the file mode, which consists of a string of 10 characters. The first column gives the file mode, which consists of a string of 10 characters. The first character indicates the file type. The nine characters after the file type are the file permissions, which are displayed in three sets of three characters each.

The second column gives the number of filenames or links associated with the file.

(continue....)The third column gives the file ownership. The third column

displays the owner of the file.

The fourth column shows the group ownership of each file. At the time of user account creation, the system administrator assigns the user to a group.

The fifth column displays the file size in bytes.The sixth column gives the date and time of modification of the files. The last column gives the name of the file and the list is arranged in the alphabetical order.5. Write a UNIX command to display the current date in the form

dd/mm/yyyy.Ans. $ date +%D

6. Explain the different types of files in UNIX.Ans. There are four possible types of file in UNIX:

Ordinary files: These files cannot contain text, data, or program information. An ordinary file cannot contain another file, or directory. An ordinary file can be a text file or a binary file.

Directory files: Directories are containers that can hold files, and other directories. A directory is actually implemented as a file that has one line for each item contained within the directory.

Special files: These files represent input/output (i/o) devices, like a tty (terminal), a disk drive, or a printer. Because UNIX treats such devices as files, some of the commands used to access ordinary files will also work with device files. This allows for more efficient use of software.

Links: A link is a pointer to another file. Since a directory is a list of the names and i-numbers of files, a directory entry can be a hard link, in which the i-number points directly to another file.

1. Write a UNIX command to count how many users have logged on to the UNIX system.

Ans. who –q2. What is a process? Explain the mechanism of process

creation in UNIX system.Ans. A process is born when a program starts execution and exists as long as the program is running. After execution the process is said to die. The name of the process is usually the name of the program being executed.

The creation of a process is in three phases and uses three system calls known as fork, exec and wait. ‘fork’ is a system call that creates a new process from an existing process. The new process is called the child process, and the existing process is called the parent. The attributes of the parent and child are an identical image except for parameters like Parent-ID. The child gets a new Parent-ID and the process is forked. This is the mechanism used to multiply process in the system. The child process overwrites the image with a copy of program that is to be executed by using the ‘exec’ system call. No additional processes are created and the

existing program is replaced with a new program. The Parent-ID of this process is the same as that of the child process which was forked.

The ‘wait’ system call is executed by the parent process to wait for the child process to get completed. The exit status of the child process is picked up by the parent process.3. What is a filter? Explain any five filters in UNIX system.Ans. Filters are UNIX commands which are used for extracting related information from a given file.

Five mainly used filters in UNIX are –a. Paginating Files, ‘pr’ :- This command, i.e. ‘pr’, prepares

a file for printing by adding suitable headers, footers and formatted text. This command has to be used with a file name as an argument –

$ pr emp.lstb. ‘head’ :- This command, as the name implies, displays

the top of the file. When used without an option, it displays the first ten lines of the file. When used with –n option, it displays the first ‘n’ number of lines.

$ head emp.lst $ head –n 3 emp.lst

c. ‘tail’ :- The tail command displays the end of the file(as opposite to head command). Like head, it displays the last 10 lines when used without arguments and with –n option, it displays the last ‘n’ number of lines.

$ tail emp.lst $ tail –n 4 emp.lst

d. ‘cut’ :- The features of the ‘cut’ command will be illustrated with specific reference to the file “shortlist”, which stores the first five lines of ‘emp.lst’ file. We can extract both columns and fields from this file with the ‘cut’ command. Columns are specified with –c optionand fields with –f option.

Cut is powerful text manipulator often used in combination with other commands or filters

Cut uses the tab as the default field delimiter, but can also work with different delimiter.

e. ‘grep’ :- The ‘grep’ command in UNIX is used to search for a pattern in a given file. It displays the selected pattern, the line numbers or the file names where the pattern occurs. The syntax is :

$ grep options pattern filename(s)‘grep’ searches for pattern in one or more filenames. The

first argument is the pattern and ones remaining are filenames.

4. Write a shell script to check whether given year is a leap year or not.

Ans. The script will be as –echo “Enter the Year : ”read yearleap = `expr $year % 4`if test $leap –eq 0thenecho “$year is a leap year.”elseecho “$year is not a leap year”fi

5. What is the significance of write and talk command in UNIX.

Ans. Write and talk are communication programs that allow users to talk to each-other in a network.

The “write” command copies lines from one user’s terminal to that of another user. The command is used by typing the following –

$ write usernamewhere username is another logged in user. The recipient gets a message from the sender along with the sender’s username. If the recipient of the message now writes back, communication will start between the two users and continues until an end-of-file is read from the terminal or an interrupt is sent

How is UNIX different from other operating systems?

Ans.

The differences between UNIX and other operating systems are:

UNIX is a multi-user operating system. Unlike DOS and Windows, a number of users can access the UNIX operating system simultaneously.

UNIX has better scalability than Windows OS. UNIX is stable and can be operated continuously

without being rebooted compared to Windows

OS.

. What is the meaning of multitasking?

Ans.

A multitasking operating system allows a computer to run several programs at the same time. The multitasking operating system divides the CPU time among various processes and gives an impression of doing many tasks at the same time. The concept of dividing CPU time is known as time-sharing.

How are commands located in Unix?

Ans.

The commands can be located using the type command in Unix.

2. How does the type command work?

Ans.

The type command returns the location of the command that is passed as a parameter to the type command. For example,

$ type who

When the above command is entered, the shell searches for the command in the search path specified in the PATH environmental variable. If the command is found, the command's location is disp. How do you stop and resume the scrolling of the screen display?

Ans.

You can stop scrolling of the screen display by pressing CTRL-s and resume scrolling by pressing CTRL-q keys from the keyboard.

layed on the console.

How do you get one-line descriptions of any command in Unix?

Ans.

You can get one-line description of any command by using the whatis command in Unix. For example, to see the one-line description of cat command, you specify the following command:

$ whatis cat

Use the cal command to find out whether the year 1900 was a leap year.

Ans.

The following command can be used to find whether the year 1900 is a leap year or not:

$ cal 2 1900

As the output is showing 28 days in February, 1900 was not a leap year.

2. Use the echo command to display the message 'Good Morning'. The cursor should move to the next line after displaying the message.

Ans.

The command to display 'Good Morning' using the echo command is:

$ echo "Good Morning"

3. Display the current date in the mm/dd/yy format.

Ans.

The command to display current date in mm/dd/yy format is:

$ date +"%D"

4. Use bc to divide 35 by 9. Set the scale to 2.

Ans.

The following command is given for using the bc:

$ bc

scale=2

35/9

5. Record your login session into a file.

Ans.

The following command is given to record the login session into a file:

$ script <name of the script file>

6. List out the users logged on into the system.

Ans.

The command to list the current users is:

$ who

7. Display your terminal filename.

Ans.

The command to display the terminal file name is:

$ tty

8. Display the release version of your operating system.

Ans.

The command to display the release version of the operating system is:

$ uname -r

9. How do you check a file for spelling errors?

Ans.

A file can be checked for spelling errors by using the ispell command.

10. How do you lock your terminal for 20 minutes?

Ans.

The command to lock the terminal for 20 minutes is:

lock -20

11. How do you check your terminal settings?

Ans.

You can check your terminal settings using the stty command.

What happens if a directory has permissions 777?

Ans.

If a directory has 777 permissions, all the users have read, write, and execute permissions on that particular directory. They can add, delete, or modify any file present in that directory

How are default file and directory permissions changed?

Ans.

The default file and directory permissions can be changed using the umask command. For example,

umask 022

The above command sets the following permissions on a newly created files:

Read and Write permissions for file owner. Read permission for group owner. Read permission for other users.

How are hard links created?

Ans.

The hard links are created using the ln command.

8. What are the uses of hard links?

Ans.

The uses of hard links are:

a. Hard links prevent accidental deletion of files.

b. Hard links can make the files available to the users, when files in a directory are shifted to another directory.

How do you order the list of files by their modification time?

Ans.

The command to list the files based on their modification time is:

$ ls -t

11. Find all the directories in the /usr directory?

Ans.

The command to find all the directories in the /usr directory is:

find /usr -type d -print

1. How do you do the following using vi:

a. delete a line

b. overwrite text

c. move the cursor four lines down

d. add a new line above a line of text

e remove two lines from the end of a text and add it to the beginning of the file

f. open a file and move to the fifteenth line in the file

Ans.

a. dd

b. R

c. 4j

d. O

e. Keep the cursor at the second last line and in the escape mode press 2Y, press 1G, and press P.

f. Type vi <file name> at the shell prompt, press 15G in the escape mode.

3. How do you replace all the occurrences of the word printf with fprintf in a file?

Ans.

The following command needs to be given in the vi editor in escape mode to replace the word printf with fprintf in a file:

:1, $s/printf/fprintf/gp

4. What are the different ways of coming out of vi after saving the file?

Ans.

There are three different ways to quit vi after saving the file:

a. :wq

b. :x

c. ZZ5. How do you yank and paste lines?

Ans.

To yank and paste the lines, perform the following steps:

a. Keep the cursor at the line you want to copy.

b. Press Y or <n>Y, where n is the total number of lines that you want to copy.

c. Place the cursor at the line, where you want to paste the copied lines.

d. Press p to paste the line after the cursor or press P to paste the lines before the cursor.

4. How do you run a process in the background?

Ans.

To run a process in the background, you need to append & symbol to the command. For example,

$ wc Report &

The above command will count the characters, words, and lines in the Report file in the background.