How to use the ssh-keygen Command in Linux

Secure Shell (also known as SSH) is a cryptographic network protocol. Ssh-keygen is a tool in the Linux distro that is used for creating new authentication key pairs for SSH. Such key pairs are used for automating logins, single sign-on, and for authenticating hosts. In simple word, ssh keygen allow a user to connect to a remote system without supplying a password

It is also used to transfer files from one computer to another computer over the network using a secure copy (SCP) Protocol.

In this tutorial post, we will show you how to set up and use password-less login on Linux/Ubuntu, RHEL/CentOS, and Fedora using ssh keys to connect to remote Linux servers without entering a password. By using Password-less login with SSH keys will increase the trust-relation between two Linux servers for easy file synchronization or transfer.

In this example, we will set up SSH password-less automatic login from server 192.168.1.101 as user sr to 192.168.1.102 with user server.

Note:- Username in First Server 192.168.1.101 is :- sr

           Username in Second Server 192.168.1.102 is :- server

In your case IP address's and username would be different

Step 1: Create Authentication RSA SSH-Keygen Keys on – (192.168.1.101)

First login into server 192.168.1.101 with user sr and generate a pair of public keys using the following command.

sr@vetechno:~$  ssh-keygen -t rsa

Step 2: Now we create .ssh Directory on – 192.168.1.102

Use SSH from server 192.168.1.101 to connect server 192.168.1.102 using server as a user and create .ssh directory under it, using the following command.

Note:- Username in First Server 192.168.1.101 is :- sr

          Username in Second Server 192.168.1.102 is :- server

sr@vetechno:~$  ssh server@192.168.1.102 mkdir -p .ssh

Step 3: Upload/Move Generated Public Keys to Second Server – 192.168.1.102

Now use SSH from First Server 192.168.1.101 and upload a new generated public key (id_rsa.pub) on Second Server 192.168.1.102 under server‘s .ssh directory as a file name authorized_keys.

sr@vetechno:~$   cat .ssh/id_rsa.pub | ssh server@192.168.1.102 'cat >> .ssh/authorized_keys'

Step 4: Now we need to set Permissions on Second Server – 192.168.1.102

Set the remote ~/.ssh directory permissions to 700. Due to different SSH versions on servers, we need to set permissions on .ssh directory and authorized_keys file.

sr@vetechno:~$   ssh server@192.168.1.102 "chmod 700 .ssh; chmod 640 .ssh/authorized_keys"

Step 5: Login from First Server – 192.168.1.101 to Second Server – 192.168.1.102 Server without Password

From now onwards you can log into Second Server 192.168.1.102 as server user from First server 192.168.0.12 as sr user without a password.

sr@vetechno:~$   ssh server@192.168.1.102

Conclusion:

Congratulations you have successfully generated RSA ssh keygen to login server without Passwords. 

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