SSH Passwordless Login

• To set up passwordless SSH login between two servers, typically with public key authentication, follow these steps:

1. Generate an RSA key pair on the server you’re copying from:

   ssh-keygen -t rsa -b 4096 -C "username@hostname"

2. Copy the public key to the destination server using ssh-copy-id:

   ssh-copy-id user@destination-server

   Or, if ssh-copy-id is not available, manually copy the public key from your local .ssh/id_rsa.pub file:

   cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
   chmod 700 ~/.ssh
   chmod 600 ~/.ssh/authorized_keys
   chown -R `whoami`:`whoami` ~/.ssh

3. Add the destination server to your local /etc/hosts.deny (optional):

   : deny from all

   This helps prevent any unauthorized logins.

4. Configure sshd_config on the destination server if necessary, such as setting PermitRootLogin and PasswordAuthentication, which you might want to disable for security reasons:

   sudo cat << EOF > /etc/ssh/sshd_config
   # Custom configuration options...
   PasswordAuthentication no
   PermitRootLogin no
   # ...
   EOF

 
5. **Restart the SSH service** on both servers:
 

sudo systemctl restart sshd

 
Now, you should be able to log in from one server to another using just your private key:
 

ssh user@destination-server

 
You'll be prompted once to confirm the public key fingerprint on the destination server. After that, SSH login will be passwordless.
 
**Note**: The specific commands might vary slightly based on your Linux distribution and version or if you're running macOS or Windows using Cygwin, Git Bash, etc. Always refer to your system's documentation for precise steps.