Option 1: Restore Traditional ssh.service Mode

This approach is the easiest to understand and is suitable if you previously managed the SSH port through /etc/ssh/sshd_config.

Disable Socket Activation and Enable SSH Service

sudo systemctl disable --now ssh.socket
sudo systemctl enable --now ssh.service

Check Current SSH Port Configuration

grep -n '^Port' /etc/ssh/sshd_config /etc/ssh/sshd_config.d/* 2>/dev/null

If no custom port is configured, add the following line to /etc/ssh/sshd_config:

Port <CUSTOM_PORT>

Restart SSH Service

sudo systemctl restart ssh.service

Verify Listening Port

sudo ss -ltnp | grep <CUSTOM_PORT>

If you see output such as:

*: <CUSTOM_PORT>

or

0.0.0.0:<CUSTOM_PORT>

then the configuration has been applied successfully.

Option 2: Keep ssh.socket and Change the Listening Port

If you prefer Ubuntu’s newer socket-activation approach, modify ssh.socket instead of sshd_config.

Create a Systemd Override

sudo mkdir -p /etc/systemd/system/ssh.socket.d
sudo nano /etc/systemd/system/ssh.socket.d/listen.conf

Add the following content:

[Socket]
ListenStream=
ListenStream=<CUSTOM_PORT>

Reload and Restart

sudo systemctl daemon-reload
sudo systemctl restart ssh.socket
sudo systemctl status ssh.socket
sudo ss -ltnp | grep <CUSTOM_PORT>

Important Note

The following line is critical:

ListenStream=

It clears the default listening port before setting the new one.

Without this line, systemd may continue listening on both the default SSH port and the custom port simultaneously.