How to Configure SSH Passwordless Login on RHEL 7

How to Configure SSH Key Pair Authentication on RHEL 7/CentOS 7/RHEL 8/CentOS 8

SSH stand for Secure Shell or Secure Socket Shell. SSH is use to take Shell session securely, SSH is a cryptographic network protocol. Secure Socket Shell (SSH) is a network protocol that use port 22 of Transmission Control Protocol (TCP) and it is work on transport layer through application layer of OSI Model. The main purpose of Secure Socket Shell (SSH) is to take remote session securely. By use of Secure Socket Shell (SSH) data is encrypted between the computers means client and server, and Secure Socket Shell (SSH) protocol transfer the files securely. Secure Socket Shell (SSH) is the replacement of insecure terminal like telnet, rsh (remote shell) and rlogin (remote login) because Secure Socket Shell (SSH) provide a secure channel or tunnel for connectivity between client machine and server machine. For transferring a file, Secure Socket Shell (SSH) is also replacement of File transfer protocol due to its security feature.

Secure Socket Shell (SSH) is use to manage Linux base operating system by use of putty or tera term, routers, virtualization (VMware vCenter), servers and etc.

SSH Key Pair:

Secure Socket Shell (SSH) key pair is Private and Public Key Pair; user can login to other system without password that is Single Sign on (SSO). Secure Socket Shell (SSH) Key Pair use public key infrastructure algorithm that is a secure authentication without password. The Secure Socket Shell (SSH) key pair is use to secure the access credential by the use of private and public key, public key is store on server where user want to take Secure Socket Shell (SSH) remote session and private key is store on client machine that is a user machine to take the Secure Socket Shell (SSH) remote session.

Note: The important point is that to create a username for SSH key pair authentication on server and client both machine should have same name with same id.

To create User with name “Owais” and set its password on linux operating system (CentOS 7/RedHat7/CentOS 8/RedHat 8), type the below mention command.

useradd owais

passwd owais

To check the user id owais, type the below mention command.

id owais

To check the IP of host "rhel7" on which server user want to take the remote session, type the below mention command.

ip a

Create a user with name “owais” on client machine have hostname “Redhat7lvm” with a same name, id and password that similar to server host, from this client machine user will take the ssh session of server.

To check the id “owais” on client host “Redhat7lvm”, type the below mention command.

id owais

To check the IP address of client machine “Redhat7lvm”, type the below mention command.

ip a

To configure a server for SSH Key Pair Authentication. Create a key pair authentication of user “owais” for login with a common user “owais” on SSH server host, type the below mention command. Here public key is use for server and private key is use for client.

ssh-keygen -t rsa

In the above procedure if you not provide password, there is no need to provide password for ssh from client machine to server machine or in script. Otherwise, in the above procedure if you set password you need to provide password for ssh from client machine to server machine or in script

Move the file “id_rsa.pub” on server machine from directory “/home/owais/.ssh/id_rsa.pub” to file "authorized_keys" “/home/owais/.ssh/authorized_keys” for authorization. In other words you can say rename the file "id_rsa.pub" to file "authorized_keys" in directory ".ssh".

mv ~/.ssh/id_rsa.pub ~/.ssh/authorized_keys

To move the secret key from the server machine to client machine for login with key authentication means without password, follow the procedure.

Create a directory “.ssh” on user home location “/home/owais/” in client machine.

mkdir ~/.ssh

Set permission of directory “.ssh” to 700 on client machine, use chmod command to set the permission.

chmod 700 /home/owais/.ssh

Copy secret key “id_rsa” from server machine ssh directory to client machine ssh directory.

scp owais@10.0.*.*:/home/owais/.ssh/id_rsa /home/owais/.ssh/

To verify the ssh connectivity that key pair authentication is working, means user should login through SSH from client machine to server machine without password.

ssh -i /home/owais/.ssh/id_rsa owais@10.0.*.*

ssh owais@10.0.*.*

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