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List of E-Books Available

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Cisco Packet Tracer - Networking Simulation Tool

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Enroll, download, and get started learning valuable tips and best practices for using the latest version of Packet Tracer with our brief introductory course.

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This is the command Terminal that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator

PROGRAM:

NAME

Terminal - GNUstep Terminal Emulator

SYNOPSIS

DESCRIPTION

This manual page documents briefly the Terminal GNUstep application. This manual page was
written for the Debian distribution because the original program does not have a manual
page.

Terminal provides terminal emulation in a GNUstep environment. It gives colorized
terminals with configurable fonts, and also allows users to configure shell utilities as
GNUstep services.

Fonts
You can change the fonts used for normal and bold text in the preferences panel. Terminal
will get the metrics for the character cells from the normal font, so this font really
should be a fixed pitch font or things will look messed up. The bold font should closely
match the normal font.

Terminal assumes that all characters, bold and normal, stay inside the normal font's
bounding box. If they don't, there will be visual glitches. However, it is more common
that a non-fixed pitch font's bounding box is very large (since it needs to enclose all
characters in the font), so that the terminal window will be very wide.

Keys
By default, the command key is used to access key equivalents for menu entries, and thus
can't be used as a meta key in the terminal. If you have command mapped to the key you
want to use as meta, you can enable `Treat the command key as meta' in the preferences
panel. However, this will disable all key equivalents in Terminal. The `proper' solution
to this problem is to remap the command key (and possibly alternate key). The alternate
key will always be treated as meta.

Often, the escape key can be used to emulate a meta key. This means that in some
programs, you might have to press escape twice to get a `real' escape, or there will be a
delay before it is handled. The `Send a double escape...' option causes Terminal to send
a double escape when you hit the escape key (ie. "\e\e"), which should work better (but
you can no longer use the escape key as meta).

Terminal services
Terminal can provide services for other applications by piping the selection through
arbitrary commands. Services are configured in one of the preferences panel's tabs. The
first time you open this tab, a default set of services will be loaded. To save these
where make_services will actually find them, press `Apply and save'. This will also run
make_services to update the services list, but it may take up to 30 seconds for running
applications to notice the change.

The `Add' and `Remove' buttons add and remove services. Using the `Export' button it is
possible to save a set of services to a file. These files can be imported using the
`Import' button, so it is possible for users to share terminal services definitions. The
extension of the file should be `.svcs'. The default set of services is such a file
located in the application wrapper's resource directory. If you import a service with the
same name as an existing service, and they aren't identical, the new one will be renamed
to avoid a conflict.

Name
This is the name of the service as it appears in the services menu. By default,
terminal services will be placed in a `Terminal' submenu of the Services menu, but
you can override this by giving the name a leading `/'. In this case, you can also
use a second `/' to create your own submenus. (gnustep-gui doesn't support submenus
of submenus, though.) Names must be unique.

Key The key equivalent for this command, if any. Note that if an application uses this
key for some other menu entry, the key will activate that menu entry, not the
service.

Command line
The command line. It is passed to /bin/sh, so any shell commands will work, and
arguments may have to be quoted. A `%p' in the command line will cause a prompt to
be brought up when the service is run. If input is to be placed on the command
line, you can mark the place to put it at with `%s' (otherwise it will be appended
to the command line). You can use `%%' to get a real `%'.

Run in background/new window/idle window
If a service is set to run in the background, the command will have to complete
before the service will return, and the service can return output. Otherwise, the
command's output will appear in a window. ``new window'' causes a completely new
window to be opened (and it will close automatically when the command is completed
if that option is set). ``idle window'' causes Terminal to try to reuse an
existing idle window. If there is no such window it will open a new window (and
that window won't close automatically).

Ignore/return output (only applies to background services)
If set to ignore, the output of the command will be discarded. Otherwise, it will
be parsed to a string or a bunch of filenames, depending on the acceptable types.
The output is assumed to be utf8 encoded.

No input/Input in stdin/Input on command line
If set to `No input', the service won't accept any input. Otherwise it is
necessary to select something to run it, and the selection will be either piped to
the command (`in stdin') or placed on the service's command line (either at the
`%s' or at the end, see above). Input will be sent to the command utf8 encoded.

Accept types
Plain text will be sent verbatim to the command. A list of filenames (possibly
just one) will be sent separated by ' ':s (if on the command line), or newlines (if
in stdin).

OPTIONS

Commands can be given on the command line which will be run in the newly opened shell
window.

EMULATION

The terminal emulation code is based on Linux's console code, and nearly all parts of it
are handled. Thus, the TERM environment variable is set to `linux'. Additionally,
`vt100', `vt220', `xterm', and others similar to these should mostly work. To distinguish
Terminal from a `real' linux console, the environment variable TERM_PROGRAM is set to
GNUstep_Terminal.

The xterm extensions for setting the window's title are also supported. You set the title
using:

' 33]'+0, 1, or 2+';'+the title+' 07'
1 sets the miniwindow title, 2 sets the window title, and 0 sets both.

Example (from Jeff Teunissen):

export PROMPT_COMMAND='echo -ne "\033]2;Terminal - ${HOSTNAME}:${PWD}\007"'

ENVIRONMENT

Terminal sets the following environment variables:

TERM Will be set to linux.

TERM_PROGRAM
Will be set to GNUstep_Terminal.

LANGUAGES

Terminal speaks English, French, German, Hungarian, Norwegian, Russian, Spanish, Italian,
Swedish and Turkish.

NOTES

The content of this manual page is taken from the packages README file and was converted
into a manual page for Debian.

Use Terminal online using onworks.net services

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Run online Terminal in free Ubuntu online, free Fedora online, free Windows online emulator or free MACOS online emulator by OnWorks

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Online Syllabus KIT's College of Engineering, Kolhapur

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An institute established in May 1983, KIT reflects the vision of leading industrialists and educationalists. The Institute has been awarded "A" status by Govt. of Maharashtra in recognition of its over all academic excellence and infrastructure. It is affiliated to Shivaji University, Kolhapur and is approved by AICTE, New Delhi.

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/****************** CLIENT CODE ****************/

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include<arpa/inet.h>

int main(){
  int clientSocket;
  char buffer[1024];
  struct sockaddr_in serverAddr;
  socklen_t addr_size;

  /*---- Create the socket. The three arguments are: ----*/
  /* 1) Internet domain 2) Stream socket 3) Default protocol (TCP in this case) */
  clientSocket = socket(PF_INET, SOCK_STREAM, 0);
  
  /*---- Configure settings of the server address struct ----*/
  /* Address family = Internet */
  serverAddr.sin_family = AF_INET;
  /* Set port number, using htons function to use proper byte order */
  serverAddr.sin_port = htons(7891);
  /* Set IP address to localhost */
  serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
  /* Set all bits of the padding field to 0 */
  memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero);  

  /*---- Connect the socket to the server using the address struct ----*/
  addr_size = sizeof serverAddr;
  connect(clientSocket, (struct sockaddr *) &serverAddr, addr_size);

  /*---- Read the message from the server into the buffer ----*/
  recv(clientSocket, buffer, 1024, 0);

  /*---- Print the received message ----*/
  printf("Data received: %s",buffer);   

  return 0;
}

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/****************** SERVER CODE ****************/

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include<arpa/inet.h>

int main(){
  int welcomeSocket, newSocket;
  char buffer[1024];
  struct sockaddr_in serverAddr;
  struct sockaddr_storage serverStorage;
  socklen_t addr_size;

  /*---- Create the socket. The three arguments are: ----*/
  /* 1) Internet domain 2) Stream socket 3) Default protocol (TCP in this case) */
  welcomeSocket = socket(PF_INET, SOCK_STREAM, 0);
  
  /*---- Configure settings of the server address struct ----*/
  /* Address family = Internet */
  serverAddr.sin_family = AF_INET;
  /* Set port number, using htons function to use proper byte order */
  serverAddr.sin_port = htons(7891);
  /* Set IP address to localhost */
  serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
  /* Set all bits of the padding field to 0 */
  memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero);  

  /*---- Bind the address struct to the socket ----*/
  bind(welcomeSocket, (struct sockaddr *) &serverAddr, sizeof(serverAddr));

  /*---- Listen on the socket, with 5 max connection requests queued ----*/
  if(listen(welcomeSocket,5)==0)
    printf("Listening\n");
  else
    printf("Error\n");

  /*---- Accept call creates a new socket for the incoming connection ----*/
  addr_size = sizeof serverStorage;
  newSocket = accept(welcomeSocket, (struct sockaddr *) &serverStorage, &addr_size);

  /*---- Send message to the socket of the incoming connection ----*/
  strcpy(buffer,"Hello World\n");
  send(newSocket,buffer,13,0);



  return 0;
}

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Slides for 『TCP/IP Protocol Suite』 4th
Ed.

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If you have been using a linux distro for quite long time now and you are not a newbee at linux anymore then you might have come across the terms like SSH and telnet. They are pretty similar when it comes to facility they provide but did SSH come into play when Telnet already existed?
SSH or Secure SHell
SSH or Secure SHell is now only major protocol to access the network devices and servers over the internet. SSH was developed by SSH Communications Security Ltd., it is a program to log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another.

It provides strong authentication and secure communications over insecure channels.

SSH runs on port 22 by default; however it can be easily changed. SSH is a very secure protocol because it shares and sends the information in encrypted form which provides confidentiality and security of the data over an un-secured network such as internet.

Once the data for communication is encrypted using SSH, it is extremely difficult to decrypt and read that data, so our passwords also become secure to travel on a public network.

SSH also uses a public key for the authentication of users accessing a server and it is a great practice providing us extreme security. SSH is mostly used in all popular operating systems like Unix, Solaris, Red-Hat Linux, CentOS, Ubuntu etc.

SSH protects a network from attacks such as IP spoofing, IP source routing, and DNS spoofing. An attacker who has managed to take over a network can only force ssh to disconnect. He or she cannot play back the traffic or hijack the connection when encryption is enabled.

When using ssh's slogin (instead of rlogin) the entire login session, including transmission of password, is encrypted; therefore it is almost impossible for an outsider to collect passwords.

Installation of the OpenSSH client and server applications is simpler.
To install it on your Ubuntu system, use this command at a terminal prompt:

$sudo apt-get update
$sudo apt install openssh-client

To install the OpenSSH server application, and related support files, use this command at a terminal prompt:

$sudo apt-get update
$sudo apt install openssh-serve

And that's pretty much it! Simple no?
Telnet
Telnet is the joint abbreviation of Telecommunications and Networks and it is a networking protocol best known for UNIX platform. Telnet uses the port 23 and it was designed specifically for local area networks.

Telnet is famous for being the original Internet when the Net first launched in 1969 and was built to be form of remote control to manage mainframe computers from distant terminals. In those original days of large mainframe computers, telnet enabled research students and professors to 'log in' to the university mainframe from any terminal in the building.

This remote login saved researchers hours of walking each semester. While telnet pales in comparison to modern networking technology, it was revolutionary in 1969, and telnet helped pave the way for the eventual World Wide Web in 1989. While telnet technology is very old, it is still in some use today by purists.

Telnet is not a secure communication protocol because it does not use any security mechanism and transfers the data over network/internet in a plain-text form including the passwords and so any one can sniff the packets to get that important information.

There are no authentication policies & data encryption techniques used in telnet causing huge security threat that is why telnet is no longer used for accessing network devices and servers over public network.

On a Ubuntu(a famous and my personal favourite linux distro.)
We can install the telnet server with following commands:

$sudo apt-get install xinetd telnetd

The service should be fired-up automatically once the installation is done. Your may also check the service status if required using:

$sudo /etc/init.d/xinetd status

To Telnet an IP:

$telnet serverip

If you would like to change its ports, you'll need to edit /etc/services with the line:

$telnet 23/tcp

Once changed, restart to apply the changes with:

$sudo /etc/init.d/xinetd restart

Right now it might looking like some tedious and wacky terminal commands but if you try to run them once on your terminal, trust me you'll find it extremely easy!

Just like SSH, Telnet is also apparently just a dull and boring terminal screen but with some unimaginable features.
Differences between SSH and Telnet

1. SSH is more secure compared to Telnet

2. SSH encrypts the data while Telnet sends data in plain text

3. SSH uses a public key for authentication while Telnet does not use any authentication

4. SSH adds a bit more overhead to the bandwidth compared to Telnet

5. Telnet has been all but replaced by SSH in almost all uses

6. SSH and Telnet commonly serves the same purpose

Lastly, there are some SSH clients, the software that you can use to setup a connection with the SSH server available for all the major operating systems and tablet operating systems.

Mac OS X & Linux: built-in, available in Terminal

Windows: PuTTY, others

Andriod: JuiceSSH, others

iOS: Prompt, others

If you want to connect your Windows PC with a Linux PC then you a software called 'PuTTY' which you can download from here.
After installation it'll look a lot like this:

References : askubuntu.com

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Difference between SSH and Telnet - GeeksforGeeks

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If you have been using a linux distro for quite long time now and you are not a newbee at linux anymore then you might have come across the terms like SSH and telnet. They are pretty similar when it comes to facility they provide but did SSH come into play when Telnet already existed?

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TELNET stands for Teletype Network. It is a client/server application protocol that provides access to virtual terminals of remote systems on local area networks or the Internet. The local computer uses a telnet client program and the remote computers use a telnet server program. In this article, we will discuss every point about TELNET.

What is Telnet?

TELNET is a type of protocol that enables one computer to connect to the local computer. It is used as a standard TCP/IP protocol for virtual terminal service which is provided by ISO. The computer which starts the connection is known as the local computer. The computer which is being connected to i.e. which accepts the connection known as the remote computer. During telnet operation, whatever is being performed on the remote computer will be displayed by the local computer. Telnet operates on a client/server principle.

History of TELNET

The Telnet protocol originated in the late 1960s, it was created to provide remote terminal access and control over mainframes and minicomputers. Initially, it was designed to be a simple and secure method of connecting to a remote system. This protocol allowed users to access remote computers using a terminal or command-line interface. Over time, Telnet's use has diminished due to security concerns, and alternatives like SSH are now preferred for secure remote management

Logging in TELNET

The logging process can be further categorized into two parts:

1. Local Login

Whenever a user logs into its local system, it is known as local login.
The Procedure of Local Login

Keystrokes are accepted by the terminal driver when the user types at the terminal.

Terminal Driver passes these characters to OS.

Now, OS validates the combination of characters and opens the required application.

2. Remote Login

Remote Login is a process in which users can log in to a remote site i.e. computer and use services that are available on the remote computer. With the help of remote login, a user is able to understand the result of transferring the result of processing from the remote computer to the local computer.

The Procedure of Remote Login

When the user types something on the local computer, the local operating system accepts the character.

The local computer does not interpret the characters, it will send them to the TELNET client.

TELNET client transforms these characters to a universal character set called Network Virtual Terminal (NVT) characters and it will pass them to the local TCP/IP protocol Stack.

Commands or text which are in the form of NVT, travel through the Internet and it will arrive at the stack at the remote computer.

Characters are then delivered to the operating system and later on passed to the TELNET server.

Then TELNET server changes those characters to characters that can be understandable by a remote computer.

The remote operating system receives characters from a pseudo-terminal driver, which is a piece of software that pretends that characters are coming from a terminal.

The operating system then passes the character to the appropriate application program.

Network Virtual Terminal(NVT)

NVT (Network Virtual Terminal) is a virtual terminal in TELNET that has a fundamental structure that is shared by many different types of real terminals. NVT (Network Virtual Terminal) was created to make communication viable between different types of terminals with different operating systems.

How TELNET Works?

Client-Server Interaction

The Telnet client initiates the connection by sending requests to the Telnet server.

Once the connection is established, the client can send commands to the server.

The server processes these commands and responds accordingly.

Character Flow

When the user types on the local computer, the local operating system accepts the characters.

The Telnet client transforms these characters into a universal character set called Network Virtual Terminal (NVT) characters.

These NVT characters travel through the Internet to the remote computer via the local TCP/IP protocol stack.

The remote Telnet server converts these characters into a format understandable by the remote computer.

The remote operating system receives the characters from a pseudo-terminal driver and passes them to the appropriate application program .

Network Virtual Terminal (NVT)

NVT is a virtual terminal in Telnet that provides a common structure shared by different types of real terminals.

It ensures communication compatibility between various terminals with different operating systems.

TELNET Commands

Commands of Telnet are identified by a prefix character, Interpret As Command (IAC) with code 255. IAC is followed by command and option codes. The basic format of the command is as shown in the following figure :

Following are some of the important TELNET commands:

Following are some common options used with the telnet:

Uses of TELNET

Remote Administration and Management

Network Diagnostics

Understanding Command-Line Interfaces

Accessing Bulletin Board Systems (BBS)

Automation and Scripting

Advantages of TELNET

It provides remote access to someone's computer system.

Telnet allows the user for more access with fewer problems in data transmission .

Telnet saves a lot of time.

The oldest system can be connected to a newer system with telnet having different operating systems.

Disadvantages of TELNET

As it is somehow complex, it becomes difficult to beginners in understanding.

Data is sent here in form of plain text, that's why it is not so secured.

Some capabilities are disabled because of not proper interlinking of the remote and local devices.

Modes of Operation

Default Mode: If no other modes are invoked then this mode is used. Echoing is performed in this mode by the client. In this mode, the user types a character and the client echoes the character on the screen but it does not send it until the whole line is completed.

Character Mode: Each character typed in this mode is sent by the client to the server. A server in this type of mode normally echoes characters back to be displayed on the client's screen.

Line Mode: Line editing like echoing, character erasing, etc. is done from the client side. The client will send the whole line to the server.

Conclusion

Telnet is a client/server application protocol that allows remote access to virtual terminals via local area networks or the internet. Telnet's use has decreased due to security concerns, with protocols such as SSH chosen for safe remote management. Telnet is still useful for remote administration, network diagnostics, instructional purposes, and interacting with legacy systems.

Frequently Asked Questions on TELNET - FAQs

What is Telnet used for?

Terminal programs typically use TELNET to allow you to log into a remote host.

Is Telnet TCP or UDP?

A TELNET connection is a Transmission Control Protocol ( TCP).

Is Telnet secure?

Telnet is inherently insecure. Credential information (usernames and passwords) supplied over telnet is not encrypted and hence vulnerable to identity theft.

Which layer is Telnet?

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A Computer Science portal for geeks. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions.

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Your All-in-One Learning Portal: GeeksforGeeks is a comprehensive educational platform that empowers learners across domains-spanning computer science and programming, school education, upskilling, commerce, software tools, competitive exams, and more.