ssh: Connection timed out.

[henkoegema]

Desktop met : Ubuntu 22.04.4 LTS x86_64  met  NoMachine (remote desktop programma)
Laptop met :   Xubuntu 24.04 LTS x86_64    met NoMachine

Met NoMachine kan ik verbinding maken van laptop naar desktop en omgekeerd.
Met ssh kan ik verbinding maken van desktop naar laptop, maar niet van laptop naar desktop.
Geen foutmelding, maar:  ssh: connection to host 192.168.43 port 22: Connection timed out.

[henkoegema]

Dit antwoord gaf GPT-4 :   
En inderdaad, hier zat de oplossing bij.
Zou ik zelf niet gevonden hebben.

Code: [Selecteer]

When you encounter a "Connection timed out" error when trying to SSH from your Xubuntu 24.04 machine to your Ubuntu 20.04 desktop, it indicates that your Xubuntu machine is unable to reach the Ubuntu machine on the network. Here are some steps to diagnose and resolve this issue:

### 1. Check Network Connectivity
Ensure both machines are on the same network and can communicate with each other.

- **Ping the Ubuntu 20.04 machine from Xubuntu 24.04:**
  ```bash
  ping <Ubuntu_IP_Address>
  ```

- **Ping the Xubuntu 24.04 machine from Ubuntu 20.04:**
  ```bash
  ping <Xubuntu_IP_Address>
  ```

If the ping command fails, there's a basic network connectivity issue that needs to be resolved first.

### 2. Verify SSH Service Status
Make sure the SSH service is running on your Ubuntu 20.04 machine.

- **Check SSH status:**
  ```bash
  sudo systemctl status ssh
  ```
  If it's not running, start it with:
  ```bash
  sudo systemctl start ssh
  ```

### 3. Check SSH Configuration
Ensure SSH is configured to listen on the correct port and network interface.

- **Check SSH configuration file (/etc/ssh/sshd_config):**
  ```bash
  sudo nano /etc/ssh/sshd_config
  ```
  Ensure the `Port` and `ListenAddress` settings are correct. The default port is 22 and usually, `ListenAddress` is set to 0.0.0.0 to listen on all interfaces.

### 4. Firewall Rules
Ensure that the firewall on Ubuntu 20.04 is not blocking SSH traffic.

- **Check UFW status:**
  ```bash
  sudo ufw status
  ```
  If UFW is active and blocking SSH, allow SSH traffic:
  ```bash
  sudo ufw allow ssh
  ```

### 5. Router/Switch Configuration
If both machines are on different networks or subnets, ensure that the router or switch between them is configured to allow SSH traffic.

### 6. Port Forwarding (if applicable)
If you are trying to SSH over the internet, make sure port forwarding is correctly set up on your router to forward port 22 to the internal IP address of your Ubuntu 20.04 machine.

### 7. SSH Client Configuration
Ensure there are no misconfigurations in the SSH client.

- **Check SSH client configuration on Xubuntu 24.04:**
  ```bash
  sudo nano /etc/ssh/ssh_config
  ```

### 8. Test with Verbose Mode
Use SSH with verbose mode to get more information about the connection attempt.

- **Verbose mode:**
  ```bash
  ssh -vvv <user>@<Ubuntu_IP_Address>
  ```

### 9. Network Tools
Use tools like `nmap` to check if the SSH port is open on the Ubuntu 20.04 machine.

- **Scan for open ports:**
  ```bash
  sudo apt install nmap
  nmap -p 22 <Ubuntu_IP_Address>
  ```

### 10. Logs
Check the SSH logs on the Ubuntu 20.04 machine for any clues.

- **SSH logs:**
  ```bash
  sudo tail -f /var/log/auth.log
  ```

### Summary of Commands
1. **Ping:**
   ```bash
   ping <Ubuntu_IP_Address>
   ```

2. **SSH Service Status:**
   ```bash
   sudo systemctl status ssh
   sudo systemctl start ssh
   ```

3. **SSH Configuration:**
   ```bash
   sudo nano /etc/ssh/sshd_config
   ```

4. **UFW Status:**
   ```bash
   sudo ufw status
   sudo ufw allow ssh
   ```

5. **Verbose SSH:**
   ```bash
   ssh -vvv <user>@<Ubuntu_IP_Address>
   ```

6. **Port Scan:**
   ```bash
   sudo apt install nmap
   nmap -p 22 <Ubuntu_IP_Address>
   ```

7. **SSH Logs:**
   ```bash
   sudo tail -f /var/log/auth.log
   ```

By following these steps, you should be able to identify and resolve the issue preventing you from SSHing into your Ubuntu 20.04 desktop from your Xubuntu 24.04 machine.

Firewall rules: 

4. **UFW Status:**
   ```bash
   sudo ufw status
   sudo ufw allow ssh     
   ```