• 27 Jul, 2026
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Setup Passwordless SSH in Linux

Setup Passwordless SSH Between node1 and node2 in Linux

Setting up Passwordless SSH enables secure authentication between Linux servers without requiring a password for every login. It is an essential configuration for PostgreSQL replication, high availability (HA), automated backups, failover management, and routine Linux administration.

In this guide, we’ll configure passwordless SSH between two Linux servers named node1 and node2 for the root user.

Note: The same process can be followed for any Linux user by replacing the root account with the required username.

Environment

Step 1: Verify Existing SSH Keys

Before generating new SSH keys, verify whether keys already exist.

Generating new keys unnecessarily may break existing passwordless SSH configurations.

On node1

ls -al ~/.ssh/id_*.pub

On node2

ls -al ~/.ssh/id_*.pub

If output appears similar to:

/root/.ssh/id_rsa.pub

then SSH keys already exist.

Skip to Step 3.

Otherwise continue to generate new SSH keys.

Step 2: Generate SSH Keys

Run the following command on both servers.

On node1

ssh-keygen

When prompted:

Enter file in which to save the key (/root/.ssh/id_rsa):

Press Enter

Enter passphrase (empty for no passphrase):

Press Enter

Enter same passphrase again:

Press Enter

Expected output:

Your identification has been saved in:

/root/.ssh/id_rsa

Your public key has been saved in:

/root/.ssh/id_rsa.pub

On node2

ssh-keygen

Again press Enter for every prompt.

Expected output:

Your identification has been saved in:

/root/.ssh/id_rsa

Your public key has been saved in:

/root/.ssh/id_rsa.pub

Step 3: View Public SSH Keys

Display the public key on each server.

On node1

cat ~/.ssh/id_rsa.pub

Copy the entire output.

On node2

cat ~/.ssh/id_rsa.pub

Copy the entire output.

Your public keys will look similar to:

ssh-rsa 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 [email protected]

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC6tidiCRszVpoXPVAK8Kfk7xNBRa8KPf57fWQH1rsOpXzhMOinZFfZTa+CG9tXpgGSBA/JQqF6wWOUyFsiQGomgauxy6G/pKUOzSebHhEsF38ElJjlP8m4ahk8IQg4DNo55/3zsYvqKJwv7nn5YeDguscEV6BtI0kngLpfp9zhpSlnt0QBjGg7JhuZAHToGJfP0ZVbBfPZOMavkZ0r3Bpg/uenZ8K6dh4EOP21P0QYcS8YxPlodWzqVnkGlHwnNLgvcQwUl81xQYPlzLZgguHYPH6HsXI5cXfEs2pF0XeNNabLoKi01fB98gcm3XHqxA/TKXAOnO1TTqi3sRpAD1n5 [email protected]

Step 4: Add Public Keys to authorized_keys

Each server must trust the other server.

This is done by placing both public keys inside the authorized_keys file.

On node1

vi ~/.ssh/authorized_keys

Paste:

• node1 public key
• node2 public key

Save the file.

On node2

vi ~/.ssh/authorized_keys

Paste:

• node1 public key
• node2 public key

Save the file.

Step 5: Set Proper Permissions

SSH is very strict about permissions.

Run the following commands on both servers.

On node1

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

On node2

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

Step 6: Test Passwordless SSH

Connect from node1 to node2

Run:

ssh root@node2

or

ssh [email protected]

The first time you connect, you’ll see:

The authenticity of host 'node2' can't be established.

ECDSA key fingerprint is SHA256:xxxxxxxxxxxxxxxxxxxx.

Are you sure you want to continue connecting (yes/no)?

Type:

yes

You should now log in without being asked for the root password.

Connect from node2 to node1

Run:

ssh root@node1

or

ssh [email protected]

Again, type:

yes

for the first connection.

You should now be able to log in without entering the password.

Verify Passwordless SSH

To confirm everything is working correctly:

From node1

ssh root@node2 hostname

Expected output:

node2

From node2

ssh root@node1 hostname

Expected output:

node1

If the hostname is displayed without prompting for a password, the passwordless SSH configuration is successful.

Common Troubleshooting Tips

If passwordless SSH does not work:

• Verify SSH keys exist:

  ls ~/.ssh

• Check permissions:

  chmod 700 ~/.ssh
  chmod 600 ~/.ssh/authorized_keys

• Ensure the SSH service is running:

  systemctl status sshd

• Restart the SSH service if required:

  systemctl restart sshd

• Confirm that both public keys are correctly added to the authorized_keys file.
• Verify that hostname resolution or IP connectivity between node1 and node2 is working.

Conclusion

Passwordless SSH is an essential Linux administration skill and is widely used in environments such as Oracle RAC, DevOps automation, Ansible, Kubernetes, and cloud infrastructure. By exchanging SSH public keys between node1 and node2, administrators can securely log in without repeatedly entering passwords, making automation and remote management significantly more efficient.