How to fix error: Bind to port 22 on 0.0.0.0 failed: Address already in use. in SSH

First, identify which process currently holds port 22. Use one of these commands:

sudo lsof -i :22

Or with netstat:

sudo netstat -tulpn | grep :22

Or with ss (modern systems):

sudo ss -tulpn | grep :22

The output will show the process name and PID. If it shows sshd is already running, you likely have a duplicate process. If it's a different service, note that name.

Stop the currently running SSH service gracefully:

sudo systemctl stop sshd

Or on older systems:

sudo service ssh stop

Wait a few seconds for the process to terminate. If it doesn't stop cleanly, check the next step.

If the service didn't stop cleanly, forcefully terminate the process:

sudo fuser -k 22/tcp

Or using the PID from your earlier lsof/netstat output:

sudo kill -9 <PID>

Verify the port is now free:

sudo lsof -i :22

This should return no results.

Review your SSH configuration for issues:

sudo grep -n "ListenAddress\|Port" /etc/ssh/sshd_config | grep -v "^#"

Look for:
- Multiple Port directives on the same line or repeated
- Multiple ListenAddress entries that could conflict
- ListenAddress directives pointing to non-existent IP addresses

If you find duplicates or invalid addresses, comment them out:

sudo nano /etc/ssh/sshd_config

For a basic setup, use just:

Port 22
ListenAddress 0.0.0.0
ListenAddress ::

Always test your sshd configuration for syntax errors before restarting:

sudo sshd -t

If no output appears, the configuration is valid. If errors appear, fix them and repeat this test.

You can also do a dry-run start:

sudo sshd -t -D

This will attempt to bind to ports but won't daemonize.

Once configuration is validated and port 22 is free, restart sshd:

sudo systemctl start sshd

Or:

sudo service ssh start

Verify it's running:

sudo systemctl status sshd

You should see "active (running)" in the output.

Test that SSH is now accepting connections:

ssh -v localhost

Or from a remote machine:

ssh user@your-server-ip

If the connection succeeds, the issue is resolved.