How to fix sshd: no hostkeys available -- exiting. in SSH

First, verify whether the host key files actually exist on your system:

ls -la /etc/ssh/ssh_host_*key*

You should see output like:
- ssh_host_rsa_key (private, mode 600)
- ssh_host_ecdsa_key (private, mode 600)
- ssh_host_ed25519_key (private, mode 600)
- ssh_host_*_key.pub files (public, mode 644)

If these files don't exist at all, proceed to Step 2. If they exist but show wrong permissions, skip to Step 3.

If the host key files don't exist, generate them using ssh-keygen:

Option A: Generate all default keys at once (recommended)

sudo ssh-keygen -A

This command automatically generates all missing key types (RSA, ECDSA, ED25519) in their standard locations.

Option B: Generate individual key types manually

sudo ssh-keygen -t rsa -b 4096 -f /etc/ssh/ssh_host_rsa_key -N ""
sudo ssh-keygen -t ecdsa -b 256 -f /etc/ssh/ssh_host_ecdsa_key -N ""
sudo ssh-keygen -t ed25519 -f /etc/ssh/ssh_host_ed25519_key -N ""

The -N "" flag means "no passphrase" (required for host keys).

After generation, verify the files exist:

ls -la /etc/ssh/ssh_host_*key*

Host key permissions must be:
- Private keys (ssh_host_*_key): 600 (readable only by root)
- Public keys (ssh_host_*_key.pub): 644 (world-readable)

Fix permissions with:

sudo chmod 600 /etc/ssh/ssh_host_*_key
sudo chmod 644 /etc/ssh/ssh_host_*_key.pub

Verify the result:

ls -la /etc/ssh/ssh_host_*

Private keys should show -rw------- (600) and public keys -rw-r--r-- (644).

Ensure ownership is correct (should be root):

sudo chown root:root /etc/ssh/ssh_host_*

Open your SSH configuration file and verify the HostKey directives point to the correct locations:

sudo grep -n "^HostKey" /etc/ssh/sshd_config

You should see entries like:

HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key

If these lines are missing or commented out (start with #), add or uncomment them:

sudo nano /etc/ssh/sshd_config

Ensure these lines are present and uncommented:

HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key

Save and exit (Ctrl+O, Enter, Ctrl+X in nano).

After generating keys and fixing permissions, restart the SSH daemon:

On systemd systems (most modern Linux):

sudo systemctl restart sshd

Verify it's running:

sudo systemctl status sshd

On older init systems:

sudo service ssh restart

Check for errors in logs:

sudo journalctl -xe -u sshd | tail -20

If you see "sshd: no hostkeys available" still, check the previous steps. If you see a different error, record that error message for further troubleshooting.

Verify SSH is now working:

ssh -v localhost

Or from another machine:

ssh username@your-server-ip

If connection succeeds, the issue is resolved. If you get a different error (e.g., "Connection refused"), the host keys are working but another issue exists (firewall, port binding, etc.).

On Debian/Ubuntu systems, you can use dpkg to regenerate SSH keys:

sudo rm /etc/ssh/ssh_host_*
sudo dpkg-reconfigure openssh-server

This removes the old keys and lets the openssh-server package regenerate them during reconfiguration. It's safe to run over an existing SSH session—your current connection won't be interrupted.

After reconfiguration, check that new keys were generated:

ls -la /etc/ssh/ssh_host_*key*