Practical uses of SSH

1. As you know, ssh is configured on port no 22. Due to security reason, your team lead asked you to change the port number. How will you perform this task?

Ans: First open the configuration file say (/etc/ssh/ssh_config) and then search for Port .Change it to the any other port number 3xxx or available port no. After doing this restart the ssh service using

 service ssh restart command.

In above diagram, as you can see we are changing the port number from 22 to 3xxx.

Benefits: It provide more security.

2. Suppose you are taking care of Linux server but forget to disable the root login.How will you disable the root login?

 Ans: First open the configuration file say (/etc/ssh/ssh_config) and then search for this string “PermitRootlogin” and make it to no. After doing this restart the ssh service.

As you can see in the above diagram we are disabling the root login.It is highly recommended not to enable the permitrootlogin in the production environment.

3. Suppose you are working with multiple numbers of Linux server and while login, every time you need to give a password.What is the solution for this?

 Ans: First create the public key as well as private key using ssh-keygen command and copy the 

 public key using ssh-copy-id to the remote server.

As you can see in the above diagram first we creating public as well as private key and copy the public key to the remote server.

 Note: After doing this verify whether you are able to login without a password or not.

4. Suppose In your organization there are multiple groups as well as users. Is it possible to give them SSH server access? If yes how will you perform this task?

Ans: First open the configuration file(/etc/ssh/ssh_config) and add users as well as group.Below is the Syntax:

AllowUsers Username

AllowGroups Groupname

 Save the file and restart the ssh service.

 As you can see in the above diagram we are adding the users as well group in the configuration file. After that restart the ssh service.

5. As you know ssh having two protocol ie is protocol 1 and protocol 2. Out of these two which one is more secure and where you have to edit these changes?

 Ans: Protocol 2 is more secure than Protocol 1. Open the configuration file and add the “Protocol 2” . After that restart the ssh service.

 As you can see in the above diagram we are adding the protocol 2 in the ssh configuration file

and then we need to restart the ssh service.

Note: In protocol 2 there are multiple authentication forms as compared to protocol 1.

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6. Suppose, you want to know the list of IP who try to do login attempt into your Linux server without proper authentication. Where are the logs will be stored?

Ans: It will be stored under /var/log/secure.It contains the information related to authentication and

authorization privileges.From the point of security, it is a very useful directory.

As you can see in the above diagram all failed login attempt information is stored in the /var/log/secure.

7. Suppose you want to access the ssh server without giving the password manually.But it should take a password from the file. Is this possible? if yes, How will you do this?

Ans: ssh username@remoteserver << filename.txt

By applying above command you don't need to enter the password manually. It will fetch the password from the file.In this way, we provide more security to our Linux server.

 As you can see in the above diagram we are login to the remote server with the help of file which contains the password information.

8. Suppose you are transferring the data using ssh connection but it is very slow. So what type of cipher will you use to increase the speed?

 Ans: Blowfish is a cipher which is used to increase the speed of data transfer by encrypting the data. A Command is: scp -c blowfish filename.txt username@remote.

 As you can see in the above diagram we are using blowfish cipher to transfer the data from local to the remote machine.

9. Suppose you are facing issue while logging to ssh server. In this case, what will you do to troubleshoot?

Ans: We will use -v option to debug the issue.Below is the command:

ssh -v username@Remotemachine

Above command give you all the logs.

 As you can see in the above diagram we are using -v option to find the login issue to the remote machine.

10. After copying a large file over the network to the ssh server. You started facing network issue. What will you do to get rid out of this problem?

Ans: We will limit the bandwidth using -l option while transferring the file over the network.Below is the command:

Scp -l 50kb/s filename username@remote-machine

l option is used to limit the bandwidth.

As you can see in the above diagram while tranferring the large file we need to limit the bandwidth to improve the network. 

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