remote commands telnet ssh

Linux/Unix SSH, Telnet Remote Commands

Comparison Chart Basis  Telnet SSH Security Less secured Highly secured port  23 22 Data format Telnet sends the  data  in plain text. Encrypted format is used to send data and also uses a secure channel. Authentication No privileges are  provided for users authentication. Uses public  key encryption for authentication. Suitability of  network Private networks  are recommended. Suitable for  Public networks. Vulnerabilities Vulnerable to  security attacks. SSH has overcome many security  issues of telnet. Bandwidth  Usage Low High

Rlogin:

1. SSH traffic is encrypted while Rlogin traffic is not
2. SSH authenticates the user while Rlogin does not
3. SSH can be used for automation while Rlogin cannot
4. Rlogin is no longer being used in favor of SSH

telnet The telnet command allows you to communicate to another host using the TELNET protocol. The telnet command is used for interactive communication with another host using the TELNET protocol. It begins in command mode, where it prints a telnet command prompt("telnet>"). If telnet is invoked with a host argument, it performs an open command implicitly (see the Commands section below for details).

SSH:

SSH which stands for Secure Shell, It is used to connect to a remote computer securely. Compare to Telnet, SSH is secure wherein the client /server connection is authenticated using a digital certificate and passwords are encrypted. Hence it's widely used by system administrators to control remote Linux servers. The syntax to log into a remote Linux machine using SSH is SSH username@ip-address or hostname Once you are logged in, you can execute any commands that you do in your terminal Linux's ssh command allows you to log into and work on a remote computer, which can be located anywhere in the world. The command (syntax: ssh hostname) opens a window on your local machine through which you can run and interact with programs on the remote machine just as if it were right in front of you. You can use the remote computer's software, access its files, transfer files, and more. An ssh session is encrypted and requires authentication.​ Ssh stands for Secure SHell, referring to the operation's inherent security. Usage Examples To log into a computer with the network id comp.org.net and username jdoe, you'd use the following command: ssh jdoe@comp.org.net If the username of the remote machine is the same as on the local machine, you can omit the username in the command: ssh comp.org.net You'll then get a message something like this: The authenticity of host 'sample.ssh.com' cannot be established. DSA key fingerprint is 04:48:30:31:b0:f3:5a:9b:01:9d:b3:a7:38:e2:b1:0c. Are you sure you want to continue connecting (yes/no)? Entering yes tells the machine to add the remote computer to your list of known hosts (~/.ssh/known_hosts). You'll see a message such as this: Warning: Permanently added 'sample.ssh.com' (DSA) to the list of known hosts. Once you're connected, you'll be prompted for a password. After you enter it, you'll get the shell prompt for the remote machine. You also can use ssh to run a command on a remote machine without logging in. For example, ssh jdoe@comp.org.net ps will execute the command ps on the computer comp.org.net and show the results in your local window. SSH or Secure Shell daemon is a network protocol that is used to perform remotely secured log ins to Linux systems via a secured channel through unsecured networks using strong cryptography. One of the most basic utility of SSH protocol is the ability to access Unix shells on remote Linux machines and execute commands. However, SSH protocol can offer other implementations, such as the ability to create secured TCP tunnels over the protocol, to remotely and securely transfer files between machines or to act as a FTP like service. The standard port used by SSH service is 22/TCP. However, you might want to change SSH default port in your Linux server, in order to achieve some kind of security through obscurity because the standard 22/TCP port is continuously targeted for vulnerabilities by hackers and bots in internet. To change SSH service default port in Linux, first you need to open the main SSH daemon configuration file for editing with your favorite text editor by issuing the below command and make the following changes. # vi /etc/ssh/sshd_config In sshd_config file, search and comment the line that begins with Port 22, by adding a hashtag (#) in front of the line. Below this line, add a new port line and specify your desired port to bind SSH. In this example, we’ll configure SSH service to bind and listen on port 34627/TCP. Make sure you choose a random port, preferably higher than 1024 (the superior limit of standard well-known ports). The maximum port that can be setup for for SSH is 65535/TCP. #Port 22 Port 34627 After you’ve made the above changes, restart the SSH daemon to reflect changes and issue netstat or ss command to confirm that SSH service listens on the new TCP port. # systemctl restart ssh # netstat -tlpn| grep ssh # ss -tlpn| grep ssh