How to change the SSH port without locking yourself out

The rule for changing the SSH port is a single one: open the new port before you close the old one, and test in a second connection before closing the first. You edit /etc/ssh/sshd_config, add a Port 2222 line (an example), open that port in the firewall, restart SSH and connect through it. Only when it works do you remove port 22. Changing the port is not real security: it clears the noise of automatic probes that only look at 22 and keeps the logs readable. Security comes from keys (creating an SSH key and keeping your VPS secure).

Step by step

1 Pick the port and write it down. A free number (above 1024) you do not use. Write it where you keep the credentials: whoever inherits the server or forgets the number cannot get in (I have lost SSH access).
2 Open the new port in the firewall first. With ufw: sudo ufw allow 2222/tcp. With firewalld: sudo firewall-cmd --permanent --add-port=2222/tcp and sudo firewall-cmd --reload. On AlmaLinux and Rocky, SELinux has to know about it too: sudo semanage port -a -t ssh_port_t -p tcp 2222 (see SELinux and AppArmor).
3 Edit the configuration keeping both ports. sudo nano /etc/ssh/sshd_config and leave the lines Port 22 and Port 2222. That way, if something goes wrong, 22 still lets you in.
4 Test the configuration before restarting. sudo sshd -t should print nothing. If it prints something, it is a syntax error: fix it before going on.
5 Restart SSH, with your current session still open. sudo systemctl restart ssh on Debian and Ubuntu; sudo systemctl restart sshd on AlmaLinux and Rocky. On recent Ubuntu releases SSH may be started by a socket (ssh.socket): see the warning below.
6 Confirm it listens on both ports. sudo ss -tlnp | grep sshd should show 22 and 2222.
7 Connect through the new one, in a new window, without closing the old one: ssh -p 2222 user@server-IP. Carry on only if you get in.
8 Remove the old port. Delete the Port 22 line, sudo sshd -t, restart, and close 22 in the firewall (sudo ufw delete allow 22/tcp). Test once more in a third window.

What changes afterwards

Tool How to give the port
ssh ssh -p 2222 user@IP
scp scp -P 2222 file user@IP:/destination (capital P)
sftp and graphical clients sftp -P 2222 ...; in a graphical client, the “Port” field
rsync rsync -e "ssh -p 2222" ... (copying with rsync)
Tunnels and automatic backups The port must be updated in every script and configuration file that connects to the server.
On recent Ubuntu releases, SSH may be started by a socket. In that case the port the system listens on can come from the ssh.socket unit and not only from sshd_config. That is why the ss -tlnp confirmation step is mandatory: if the new port does not show up, look at systemctl status ssh.socket and Ubuntu’s documentation for your release, and only then close the old one. Depending on your system, the mechanics can vary.
Never close the session where you made the change until you have tested in another. It is the most common cause of being locked out. If it happens, the panel console gets in without the network and undoes it: I have lost SSH access to my server.
Other services need to know the new port too. If you run fail2ban (installing fail2ban), tell it the new port, or it stops protecting SSH. And if you run SSH on another port because of networks that only let web traffic through, that is a different question: ports and firewall.

Locked yourself out after touching SSH? Tell us the service name and what you did, and we will give you the console.

Open a support ticket

SEE ALSO

I have lost SSH access to my server

Keeping your VPS secure

Ports and firewall on a VPS

Why your IP gets blocked by the firewall

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