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Configure SSH on Linux for Passwordless Logins to Servers

Last edited on 2026-02-23 • Tagged under  #ssh   #linux   #encrypt   #network 

Disable password logins on the Linux SERVER in favour of using SSH keys for authentication. Create the necessary SSH keys on a Linux CLIENT that will be used to secure access to remote devices.

1. Start Here

On the CLIENT and the SERVER

Create the .ssh directory and authorized_keys file in $HOME:

mkdir ~/.ssh && touch ~/.ssh/authorized_keys
chmod 700 ~/.ssh && chmod 600 ~/.ssh/authorized_keys

2. Create Public and Private Keys

On the CLIENT

Create the SSH public/private key pair protected with a passphrase using ssh-keygen:

ssh-keygen -t ed25519 -C "$(whoami)@$(uname -n)-$(date +%Y-%m-%d)"

Start ssh-agent:

if ! pidof ssh-agent > /dev/null; then eval "$(ssh-agent -s)"; fi

Add the newly-created SSH private key to the current session by running ssh-add:

ssh-add ~/.ssh/id_ed25519

Any SSH logins launched during the session will now access this key stored in memory.

3. Share Public Key

On the CLIENT

Upload the public key using ssh-copy-id to the SERVER and append to the authorized_keys file:

ssh-copy-id -i ~/.ssh/id_ed25519.pub [remote_ip_address]

Example: SERVER has a [remote_ip_address] of 178.123.1.45:

ssh-copy-id -i ~/.ssh/id_ed25519.pub 178.123.1.45

Verify key-based authentication is configured correctly by successfully logging in using ssh without a password:

ssh -o PasswordAuthentication=no 178.123.1.45

4. Disable Password Logins

On the SERVER

After verifying the SERVER can be accessed remotely using SSH keys, open sshd_config for editing:

vi /etc/ssh/sshd_config

Disable password authentication with these modifications:

PubkeyAuthentication yes
PasswordAuthentication no
KbdInteractiveAuthentication no

As an additional security measure, change the port (by default port 22) that SSH listens for connections. Changing this to a dynamic or private port between 49152 through 65535 will frustrate automated attacks.

Example: Modify the SERVER listening port from #Port 22 to Port 52222:

Port 52222

Save changes and exit.

Restart SSH:

sudo systemctl restart sshd

On the CLIENT

While remaining logged into SERVER, open another terminal and verify the changes by attempting a new login using password authentication (which should fail):

$ ssh -p 52222 -o PreferredAuthentications=password -o PubkeyAuthentication=no 178.123.1.45
<username>@178.123.1.45: Permission denied (publickey).

Verify key-based authentication continues to work as before:

ssh -p 52222 178.123.1.45

Device is now secured to accept only SSH key authentication for logins.

5. Create An Alias

On the CLIENT

Create an alias for the remote SERVER in the user ssh_config:

vi ~/.ssh/config

Add an alias for SERVER named myserver:

Host myserver
  HostName 178.123.1.45
  Port 52222

Save changes and exit.

Now a login to SERVER is simply:

ssh myserver

6. Keychain

On the CLIENT

For CLIENT devices that are not running desktop environments with their own built-in ssh key management, I like to install the keychain package to manage my keys.

When logging in for the first time after boot, it prompts me for the passphrase to unlock my key, then will maintain a single ssh-agent process across multiple login sessions.

NOTE
I rename my keys from id_ed25519* to the hostname of the device (hence the $(uname -n) below).

If using bash as the user’s SHELL, add to .bashrc:

[[ -x "/usr/bin/keychain" ]] && eval $(keychain --eval --quiet ~/.ssh/$(uname -n))

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