System Engineer Profile Q & Ans.

Q1.What is router?

Ans. Router is a layer 3 device in a network used to transfer data b/w no. of host with the help of IP address it forms a route table to forward the packet.

Q2. Role of active directory?

Ans. Active Directory is a hierarchical database; it contains info about all the objects like users, computers, groups, printers of forest. Provides information services to its clients.

Q3. How will you check if router goes down?

Ans. Every router has a LED to indicate whether the connection to the internet is healthy/not.
If the connection is healthy i.e. smooth n going.... then the LED glows Green
if the connection is unhealthy i.e. the router goes down / there is some disruption in the n/w path. Then the LED glows Amber (Yellowish Orange)

Q4. What is the advantage of sub-netting an IP address?

Ans. Subnetting is a best technique for network. When we split a large n/w into small n/w it is called Subnetting. With the help of subnetting we can reduce the N/w congestion. Because all computer broadcast for transmission. So we break huge network into small network and now broadcasting will be done only small network with the help of subnetting we can save money. Because we buy an single IP address from ISP and increase the IP address from Subnetting. That's why we can say that subnetting is best tool for increase bandwidth and save the money.

Q5. What is static ip and dynamic IP?

Ans. static IP address- administratively assignments of IP address.
Dynamic - assigning the IP address dynamically by using DHCP.

Q6. Which intermediary device regenerates data signals?

Ans. basically when our signal is weak (on a network) then we should have a repeater device. This device used to regenerate the weak signal.

Q7. What is picking and packing in computer networking?

Ans. As far as I know this term is used for items that needs to be picked from various locations in a warehouse whenever a customer fills the shopping cart and & submits the list for purchase.

Q8. What are port numbers for telnet, ftp, http and rpc?

Ans. Port is registered with IANA for the application = Official Port is not registered with IANA for the application = Unofficial Telnet = port - 23(Official) FTP = port - 20(Data Tx), 21(Command), 22(S...

Telent: 23
FTP: 22/21
HTTP: 80
RPC: 135

Q9. IIS server backup?

Ans. It’s too simply to IIS backup. Take the system state backup in that only IIS will be consider, if the server is IIS.

Q10. You want to connect a cable modem to a switch. Which cable would you use?

Ans. Straight cable.
If we use different devices we can use straight cable.
If we use same devices we can use cross cable

Q11. What is difference between ipv4 & ipv6?

Ans. IPv4 means Internet Protocol version 4, whereas IPv6 means Internet Protocol version 6.
IPv4 is 32 bits IP address that we use commonly; it can be 192.168.8.1, 10.3.4.5 or other 32 bits IP addresses. IPv4 can support up to 232 addresses, however the 32 bits IPv4 addresses are finishing to be used in near future, so IPv6 is developed as a replacement.
IPv6 is 128 bits, can support up to 2128 addresses to fulfill future needs with better security and network related features. Here are some examples of IPv6 address:
1050:0:0:0:5:600:300c:326b
ff06::c3
0:0:0:0:0:0:192.1.56.10
The most important difference is that it has a larger address space. IPv6 uses 128 bits, instead of the 32 bits used in an IPv4 address.

Q12. How does Dora process works in DHCP?

Ans. DORA stands for Discover Offer Request Ack
When there is request been sent from the client and there should be a response should be sent from the server, So the process discovering the request been sent from which client and send the Ack to the client from to server that the request is been accepted
This is was DORA concept in DHCP :)

Q13. Can infrastructure master and Global catalog be on same domain?

Ans. No because Infrastructure master performs its task by comparing its state against the state of a GC      and updates other DCs in the same domain based on the outcome. Effectively, the update would never take place since no differences would be detected.

Q14. Mac address and ip address?

Ans. This is because different types of devices use different ways of communicating to hosts. Routers for example use the IP or logical address whereas level 2 switches and older HUBS use the MAC address to communicate.

Q15. Internet connection issue?

Ans. If someone finds that their internet connectivity is down, how would you fix the problem: If someone is using a laptop they may have accidentally turned their wifi connection off This is fixed by:
Looking for the wifi connection button on the top row of the keyboard. It looks similar to the letter A surrounded by parenthesis. Push it to turn the wifi connection back on.

Q16.A user can log on to the network but has no internet connection? Explain what could be the problem.

Ans. First check the user account's membership in AD
if account is allowed to access internet check proxy settings if proxy settings are all ok update the group policy of the client machine and rerun the login script if does not work reinstall the client software.

Interview Questions

Network

Q1.What is router?

Ans. Router is a layer 3 device in a network used to transfer data b/w no. of host with the help of IP address it forms a route table to forward the packet.

Q2. Role of active directory?

Ans. Active Directory is a hierarchical database; it contains info about all the objects like users, computers, groups, printers of forest. Provides information services to its clients.

Q3. How will you check if router goes down?

Ans. Every router has a LED to indicate whether the connection to the internet is healthy/not.
If the connection is healthy i.e. smooth n going.... then the LED glows Green
if the connection is unhealthy i.e. the router goes down / there is some disruption in the n/w path. Then the LED glows Amber (Yellowish Orange)

Q4. What is the advantage of sub-netting an IP address?

Ans. Subnetting is a best technique for network. When we split a large n/w into small n/w it is called Subnetting. With the help of subnetting we can reduce the N/w congestion. Because all computer broadcast for transmission. So we break huge network into small network and now broadcasting will be done only small network with the help of subnetting we can save money. Because we buy an single IP address from ISP and increase the IP address from Subnetting. That's why we can say that subnetting is best tool for increase bandwidth and save the money.

Q5. What is static ip and dynamic IP?

Ans. static IP address- administratively assignments of IP address.
Dynamic - assigning the IP address dynamically by using DHCP.

Q6. Which intermediary device regenerates data signals?

Ans. basically when our signal is weak (on a network) then we should have a repeater device. This device used to regenerate the weak signal.

Q7. What is picking and packing in computer networking?

Ans. As far as I know this term is used for items that needs to be picked from various locations in a warehouse whenever a customer fills the shopping cart and & submits the list for purchase.

Q8. What are port numbers for telnet, ftp, http and rpc?

Ans. Port is registered with IANA for the application = Official Port is not registered with IANA for the application = Unofficial Telnet = port - 23(Official) FTP = port - 20(Data Tx), 21(Command), 22(S...

Telent: 23
FTP: 22/21
HTTP: 80
RPC: 135

Q9. IIS server backup?

Ans. It’s too simply to IIS backup. Take the system state backup in that only IIS will be consider, if the server is IIS.

Q10. You want to connect a cable modem to a switch. Which cable would you use?

Ans. Straight cable.
If we use different devices we can use straight cable.
If we use same devices we can use cross cable

Q11. What is difference between ipv4 & ipv6?

Ans. IPv4 means Internet Protocol version 4, whereas IPv6 means Internet Protocol version 6.
IPv4 is 32 bits IP address that we use commonly; it can be 192.168.8.1, 10.3.4.5 or other 32 bits IP addresses. IPv4 can support up to 232 addresses, however the 32 bits IPv4 addresses are finishing to be used in near future, so IPv6 is developed as a replacement.
IPv6 is 128 bits, can support up to 2128 addresses to fulfill future needs with better security and network related features. Here are some examples of IPv6 address:
1050:0:0:0:5:600:300c:326b
ff06::c3
0:0:0:0:0:0:192.1.56.10
The most important difference is that it has a larger address space. IPv6 uses 128 bits, instead of the 32 bits used in an IPv4 address.

Q12. How does Dora process works in DHCP?

Ans. DORA stands for Discover Offer Request Ack
When there is request been sent from the client and there should be a response should be sent from the server, So the process discovering the request been sent from which client and send the Ack to the client from to server that the request is been accepted
This is was DORA concept in DHCP :)

Q13. Can infrastructure master and Global catalog be on same domain?

Ans. No because Infrastructure master performs its task by comparing its state against the state of a GC      and updates other DCs in the same domain based on the outcome. Effectively, the update would never take place since no differences would be detected.

Q14. Mac address and ip address?

Ans. This is because different types of devices use different ways of communicating to hosts. Routers for example use the IP or logical address whereas level 2 switches and older HUBS use the MAC address to communicate.

Q15. Internet connection issue?

Ans. If someone finds that their internet connectivity is down, how would you fix the problem: If someone is using a laptop they may have accidentally turned their wifi connection off This is fixed by:
Looking for the wifi connection button on the top row of the keyboard. It looks similar to the letter A surrounded by parenthesis. Push it to turn the wifi connection back on.

Q16.A user can log on to the network but has no internet connection? Explain what could be the problem.

Ans. First check the user account's membership in AD
if account is allowed to access internet check proxy settings if proxy settings are all ok update the group policy of the client machine and rerun the login script if does not work reinstall the client software.

Networking - Interview Questions and Answers

1. Define Network?

A network is a set of devices connected by physical media links. A network is recursively is a connection of two or more nodes by a physical link or two or more networks connected by one or more nodes.

2. What is a Link?

At the lowest level, a network can consist of two or more computers directly connected by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as Link.

3. What is a node?

A network can consist of two or more computers directly connected by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as Links and the computer it connects is called as Nodes.

4. What is a gateway or Router?

A node that is connected to two or more networks is commonly called as router or Gateway. It generally forwards message from one network to another.

5. What is point-point link?

If the physical links are limited to a pair of nodes it is said to be point-point link.

6. What is Multiple Access?

If the physical links are shared by more than two nodes, it is said to be Multiple Access.

7. What are the advantages of Distributed Processing?

a. Security/Encapsulation
b. Distributed database
c. Faster Problem solving
d. Security through redundancy
e. Collaborative Processing

8. What are the criteria necessary for an effective and efficient network?

a. Performance
   It can be measured in many ways, including transmit time and response time. b. Reliability
   It is measured by frequency of failure, the time it takes a link to recover from a failure, and the network's robustness.
c. Security
   Security issues includes protecting data from unauthorized access and virues.

9. Name the factors that affect the performance of the network?

a. Number of Users
b. Type of transmission medium
c. Hardware
d. Software

10. Name the factors that affect the reliability of the network?

a. Frequency of failure
b. Recovery time of a network after a failure

11. Name the factors that affect the security of the network?

a. Unauthorized Access
b. Viruses

12. What is Protocol?

A protocol is a set of rules that govern all aspects of information communication.

13. What are the key elements of protocols?

The key elements of protocols are
a. Syntax
   It refers to the structure or format of the data, that is the order in which they are presented.
b. Semantics
   It refers to the meaning of each section of bits.
c. Timing
   Timing refers to two characteristics: When data should be sent and how fast they can be sent.

14. What are the key design issues of a computer Network?

a. Connectivity
b. Cost-effective Resource Sharing
c. Support for common Services
d. Performance

15. Define Bandwidth and Latency?

Network performance is measured in Bandwidth (throughput) and Latency (Delay). Bandwidth of a network is given by the number of bits that can be transmitted over the network in a certain period of time. Latency corresponds to how long it t5akes a message to travel from one end off a network to the other. It is strictly measured in terms of time.

16. Define Routing?

The process of determining systematically hoe to forward messages toward the destination nodes based on its address is called routing.

17. What is a peer-peer process?

The processes on each machine that communicate at a given layer are called peer-peer process.

18. When a switch is said to be congested?

It is possible that a switch receives packets faster than the shared link can accommodate and stores in its memory, for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped and in this state is said to congested state.

19. What is semantic gap?

Defining a useful channel involves both understanding the applications requirements and recognizing the limitations of the underlying technology. The gap between what applications expects and what the underlying technology can provide is called semantic gap.

20. What is Round Trip Time?

The duration of time it takes to send a message from one end of a network to the other and back, is called RTT.

21. Define the terms Unicasting, Multiccasting and Broadcasting?

If the message is sent from a source to a single destination node, it is called Unicasting.
If the message is sent to some subset of other nodes, it is called Multicasting.
If the message is sent to all the m nodes in the network it is called Broadcasting.

22. What is Multiplexing?

Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.

23. Name the categories of Multiplexing?

a. Frequency Division Multiplexing (FDM)
b. Time Division Multiplexing (TDM)
   i. Synchronous TDM
   ii. ASynchronous TDM Or Statistical TDM.
c. Wave Division Multiplexing (WDM)

24. What is FDM?

FDM is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted.

25. What is WDM?

WDM is conceptually the same as FDM, except that the multiplexing and demultiplexing involve light signals transmitted through fiber optics channel.

26. What is TDM?

TDM is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices.

27. What is Synchronous TDM?

In STDM, the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.

28. List the layers of OSI

a. Physical Layer
b. Data Link Layer
c. Network Layer
d. Transport Layer
e. Session Layer
f. Presentation Layer
g. Application Layer

29. Which layers are network support layers?

a. Physical Layer
b. Data link Layer and 
c. Network Layers

30. Which layers are user support layers?

a. Session Layer
b. Presentation Layer and 
c. Application Layer

31. Which layer links the network support layers and user support layers?

The Transport layer links the network support layers and user support layers.

32. What are the concerns of the Physical Layer?

Physical layer coordinates the functions required to transmit a bit stream over a physical medium.
a. Physical characteristics of interfaces and media
b. Representation of bits
c. Data rate
d. Synchronization of bits
e. Line configuration
f. Physical topology
g. Transmission mode

33. What are the responsibilities of Data Link Layer?

The Data Link Layer transforms the physical layer, a raw transmission facility, to a reliable link and is responsible for node-node delivery.
a. Framing
b. Physical Addressing
c. Flow Control
d. Error Control
e. Access Control

34. What are the responsibilities of Network Layer?

The Network Layer is responsible for the source-to-destination delivery of packet possibly across multiple networks (links).
a. Logical Addressing
b. Routing

35. What are the responsibilities of Transport Layer?

The Transport Layer is responsible for source-to-destination delivery of the entire message.
a. Service-point Addressing
b. Segmentation and reassembly
c. Connection Control
d. Flow Control
e. Error Control

36. What are the responsibilities of Session Layer?

The Session layer is the network dialog Controller. It establishes, maintains and synchronizes the interaction between the communicating systems.
a. Dialog control
b. Synchronization

37. What are the responsibilities of Presentation Layer?

The Presentation layer is concerned with the syntax and semantics of the information exchanged between two systems.
a. Translation
b. Encryption
c. Compression

38. What are the responsibilities of Application Layer?

The Application Layer enables the user, whether human or software, to access the network. It provides user interfaces and support for services such as e-mail, shared database management and other types of distributed information services.
a. Network virtual Terminal
b. File transfer, access and Management (FTAM)
c. Mail services
d. Directory Services

39. What are the two classes of hardware building blocks?

Nodes and Links.

40. What are the different link types used to build a computer network?

a. Cables
b. Leased Lines
c. Last-Mile Links
d. Wireless Links

41. What are the categories of Transmission media?

a. Guided Media
  i. Twisted - Pair cable
    1. Shielded TP
    2. Unshielded TP
  ii. Coaxial Cable
  iii. Fiber-optic cable
b. Unguided Media
  i. Terrestrial microwave
  ii. Satellite Communication

42. What are the types of errors?

a. Single-Bit error
  In a single-bit error, only one bit in the data unit has changed
b. Burst Error
  A Burst error means that two or more bits in the data have changed.

3. What is Error Detection? What are its methods?

Data can be corrupted during transmission. For reliable communication errors must be deducted and Corrected. Error Detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination. The common Error Detection methods are 
  a. Vertical Redundancy Check (VRC)
  b. Longitudinal Redundancy Check (VRC)
  c. Cyclic Redundancy Check (VRC)
  d. Checksum

44. What is Redundancy?

The concept of including extra information in the transmission solely for the purpose of comparison. This technique is called redundancy.

45. What is VRC?

It is the most common and least expensive mechanism for Error Detection. In VRC, a parity bit is added to every data unit so that the total number of 1s becomes even for even parity. It can detect all single-bit errors. It can detect burst errors only if the total number of errors in each data unit is odd.

46. What is LRC?

In LRC, a block of bits is divided into rows and a redundant row of bits is added to the whole block. It can detect burst errors. If two bits in one data unit are damaged and bits in exactly the same positions in another data unit are also damaged, the LRC checker will not detect an error. In LRC a redundant data unit follows n data units.

47. What is CRC?

CRC, is the most powerful of the redundancy checking techniques, is based on binary division.

48. What is Checksum?

Checksum is used by the higher layer protocols (TCP/IP) for error detection

49. List the steps involved in creating the checksum.

a. Divide the data into sections
b. Add the sections together using 1's complement arithmetic
c. Take the complement of the final sum, this is the checksum.

50. What are the Data link protocols?

Data link protocols are sets of specifications used to implement the data link layer. The categories of Data Link protocols are 1. Asynchronous Protocols
2. Synchronous Protocols
  a. Character Oriented Protocols
  b. Bit Oriented protocols

51. Compare Error Detection and Error Correction:

The correction of errors is more difficult than the detection. In error detection, checks only any error has occurred. In error correction, the exact number of bits that are corrupted and location in the message are known. The number of the errors and the size of the message are important factors.

52. What is Forward Error Correction?

Forward error correction is the process in which the receiver tries to guess the message by using redundant bits.

53. Define Retransmission?

Retransmission is a technique in which the receiver detects the occurrence of an error and asks the sender to resend the message. Resending is repeated until a message arrives that the receiver believes is error-freed.

54. What are Data Words?

In block coding, we divide our message into blocks, each of k bits, called datawords. The block coding process is one-to-one. The same dataword is always encoded as the same codeword.

55. What are Code Words?

"r" redundant bits are added to each block to make the length n = k + r. The resulting n-bit blocks are called codewords. 2ⁿ - 2^k codewords that are not used. These codewords are invalid or illegal.

56. What is a Linear Block Code?

A linear block code is a code in which the exclusive OR (addition modulo-2) of two valid codewords creates another valid codeword.

57. What are Cyclic Codes?

Cyclic codes are special linear block codes with one extra property. In a cyclic code, if a codeword is cyclically shifted (rotated), the result is another codeword.

58. Define Encoder?

A device or program that uses predefined algorithms to encode, or compress audio or video data for storage or transmission use. A circuit that is used to convert between digital video and analog video.

59. Define Decoder?

A device or program that translates encoded data into its original format (e.g. it decodes the data). The term is often used in reference to MPEG-2 video and sound data, which must be decoded before it is output.

60. What is Framing?

Framing in the data link layer separates a message from one source to a destination, or from other messages to other destinations, by adding a sender address and a destination address. The destination address defines where the packet has to go and the sender address helps the recipient acknowledge the receipt.

40 Basic Linux Command Line

1.  Everything in Linux is a file including the hardware and even the directories.

2. # : Denotes the super(root) user

3.  $ : Denotes the normal user

4.  /root: Denotes the super user’s directory

/home: Denotes the normal user’s directory.

5.  Switching between Terminals

§  Ctrl + Alt + F1-F6: Console login

§  Ctrl + Alt + F7: GUI login

6.  The Magic Tab: Instead of typing the whole filename if the unique pattern for a particular file is given then the remaining characters need not be typed and can be obtained automatically using the Tab button.

7.   ~(Tilde): Denotes the current user’s home directory

8.   Ctrl + Z: To stop a command that is working interactively without terminating it.

9.  Ctrl + C: To stop a command that is not responding. (Cancellation).

10.  Ctrl + D: To send the EOF( End of File) signal to a command normally when you see ‘>’.

11.  Ctrl + W: To erase the text you have entered a word at a time.

12.  Up arrow key: To redisplay the last executed command. The Down arrow key can be used to print the next command used after using the Up arrow key previously.

13.  The history command can be cleared using a simple option –c (clear).

14.  cd :   The cd command can be used trickily in the following ways:

cd : To switch to the home user

cd * : To change directory to the first file in the directory (only if the first file is a directory)

cd .. : To move back a folder

cd - : To return to the last directory you were in

15.  Files starting with a dot (.) are a hidden file.

16.   To view hidden files: ls -a

17.   ls: The ls command can be use trickily in the following ways:

ls -lR : To view a long list of all the files (which includes directories) and their subdirectories recursively .

ls *.* : To view a list of all the files with extensions only.

18.   ls -ll: Gives a long list in the following format

drwxr-xr-x 2 root root 4096 2010-04-29 05:17 bin where

drwxr-xr-x : permission where d stands for directory, rwx stands for owner privilege, r-x stands for the group privilege and r-x stands for others permission respectively.

Here r stands for read, w for write and x for executable.

2=> link count

root=>owner

root=>group

4096=> directory size

2010-04-29=>date of creation

05:17=> time of creation

bin=>directory file(in blue)

The color code of the files is as follows:

Blue: Directory file

White: Normal file

Green: Executable file

Yellow: Device file

Magenta: Picture file

Cyan: link file

Red: Compressed file

File Symbol

-(Hyphen) : Normal file

d=directory

l=link file

b=Block device file

c=character device file

19.  Using the rm command: When used without any option the rm command deletes the file or directory ( option -rf) without any warning. A simple mistake like rm / somedir instead of rm /somedir can cause major chaos and delete the entire content of the /(root) directory. Hence it is always advisable to use rm command with the -i(which prompts before removal) option. Also there is no undelete option in Linux.

20.  Copying hidden files: cp .* (copies hidden files only to a new destination)

21. dpkg -l : To get a list of all the installed packages.

23. Use of ‘ > ‘ and ‘ >> ‘ : The ‘ > ‘ symbol ( input redirector sign) can be used to add content to a file when used with the cat command. Whereas ‘ >> ‘ can be used to append to a file. If the ‘ >> ‘ symbol is not used and content is added to a file using only the ‘>’ symbol the previous content of the file is deleted and replaced with the new content.

e.g: $ touch text (creates an empty file)

$ cat >text

This is text’s text. ( Save the changes to the file using Ctrl +D)

$cat >> text

This is a new text. (Ctrl + D)

Output of the file:

This is text’s text.

This is a new text.

23.  To count the number of users logged in : who |wc –l

24.  cat:  The cat command can be used to trickly in the following way:

- To count no. of lines from a file : cat <filename> |wc -l

- To count no. of words from a file : cat <filename> |wc -w

- To count no. of characters from a file : cat <filename> |wc –c

25.  To search a term that returns a pattern: cat <filename> |grep [pattern]

26.  The ‘tr’ command: Used to translate the characters of a file.

tr ‘a-z’ ‘A-Z’ <text >text1 : The command for example is used to translate all the characters from lower case to upper case of the ‘text’ file and save the changes to a new file ‘text1′.

27.  File permission using chmod: ‘chmod’ can be used directly to change the file permission of files in a simple way by giving the permission for root, user and others in a numeric form where the numeric value are as follows:

r(read-only)=>4

w(write)=>2

x(executable)=>1

e.g. chmod 754 text will change the ownership of owner to read, write and executable, that of group to read and executable and that of others to read only of the text file.

28.  more: It is a filter for paging through text one screenful at a time.

Use it with any of the commands after the pipe symbol to increase readability.

e.g. ls -ll |more

29.  cron : Daemon to execute scheduled commands. Cron enables users to schedule jobs (commands or shell scripts) to run periodically at certain times or dates.

1 * * * * echo “hi” >/dev/tty1 displays the text “hi” after every 1 minute in tty1

.—————- minute (0 – 59)

| .————- hour (0 – 23)

| | .———- day of month (1 – 31)

| | | .——- month (1 – 12) OR jan,feb,mar,apr …

| | | | .—– day of week (0 – 7) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat

* * * * * command to be executed

Source of example: Wikipedia

30.  fsck: Used for file system checking. On a non-journaling file system the fsck command can take a very long time to complete. Using it with the option -c displays a progress bar which doesn’t increase the speed but lets you know how long you still have to wait for the process to complete.

e.g. fsck -C

31.  To find the path of the command: which command

e.g. which clear

32. Setting up alias: Enables a replacement of a word with another string. It is mainly used for abbreviating a system command, or for adding default arguments to a regularly used command

e.g. alias cls=’clear’ => For buffer alias of clear

33.  The du (disk usage) command can be used with the option -h to print the space occupied in human readable form. More specifically it can be used with the summation option (-s).

e.g. du -sh /home summarizes the total disk usage by the home directory in human readable form.

34.  Two or more commands can be combined with the && operator. However the succeeding command is executed if and only if the previous one is true.

e.g. ls && date lists the contents of the directory first and then gives the system date.

35.  Surfing the net in text only mode from the terminal: elinks [URL]

e.g: elinks www.google.com 

Note that the elinks package has to be installed in the system.

36.  The ps command displays a great more deal of information than the kill command does.

37.  To extract a no. of lines from a file:

e.g head -n 4 abc.c is used to extract the first 4 lines of the file abc.c

e.g tail -n 4 abc.c is used to extract the last 4 lines of the file abc.c

38.  Any changes to a file might cause loss of important data unknowingly. Hence    Linux creates a file with the same name followed by ~ (Tilde) sign without the recent changes. This comes in really handy when playing with the configuration files as some sort of a backup is created.

39.   A variable can be defined with an ‘=’ operator. Now a long block of text can be assigned to the variable and brought into use repeatedly by just typing the variable name preceded by a $ sign instead of writing the whole chunk of text again and again.

e.g ldir=/home/my/Desktop/abc

cp abcd $ldir copies the file abcd to /home/my/Desktop/abc.

40. To find all the files in your home directory modified or created today: