The paramiko.ssh_exception.NoValidConnectionsError is a specific type of exception raised by Paramiko when it attempts to establish an SSH connection but fails to connect to any of the resolved IP addresses for the given hostname and port. This error essentially means: “I tried all the ways I know to connect to that server, and none of them worked.” It’s a strong indicator of underlying network connectivity or server reachability issues, rather than authentication problems.
This error often wraps one or more lower-level socket errors (e.g., connection refused, host unreachable, timeout), which can be inspected to pinpoint the exact cause.
General Debugging Steps for Paramiko
To get more detailed information about why the connection attempts failed, enable Paramiko’s verbose logging. This is your first and most important step.
import paramiko
import logging
# Set up logging for Paramiko
logging.basicConfig()
paramiko.util.log_to_file("paramiko.log") # Log to a file
# For immediate console output, you can use:
# logging.getLogger("paramiko").setLevel(logging.DEBUG)
# logging.getLogger("paramiko.transport").setLevel(logging.DEBUG) # Even more specific
try:
client = paramiko.SSHClient()
client.set_missing_host_key_policy(paramiko.AutoAddPolicy()) # Or RejectPolicy for production
client.connect(
hostname='your_server_ip_or_hostname',
port=22, # Or your custom SSH port
username='your_username',
password='your_password', # Or pkey=your_pkey
timeout=10 # Important for network issues
)
print("Connected successfully!")
client.close()
except paramiko.ssh_exception.NoValidConnectionsError as e:
print(f"No valid connections could be established: {e}")
# Inspect wrapped errors for more detail
if hasattr(e, 'errors') and e.errors:
print("Underlying connection errors:")
for addr, err in e.errors.items():
print(f" {addr}: {err}")
except Exception as e:
print(f"An unexpected error occurred: {e}")
After running your script with logging enabled, examine the paramiko.log file (or your console output) for messages like “Connection refused,” “Network is unreachable,” “Operation timed out,” or “Name or service not known.” These messages will guide your troubleshooting.
Common Causes and Solutions for NoValidConnectionsError
1. Incorrect Hostname or IP Address
Cause: A typo in the hostname or IP address, or the hostname simply doesn’t resolve to a valid IP address.
Solution:
- Verify: Double-check the hostname or IP address for typos.
- Ping/Nslookup: Use ping or nslookup (or dig) from your client machine to verify the hostname resolves and is reachable.
ping your_server_hostname_or_ip nslookup your_server_hostname - DNS Issues: If using a hostname, ensure your client’s DNS resolver is correctly configured and can resolve the server’s hostname.
2. Incorrect Port Number
Cause: The SSH server is listening on a port other than the default (22), and your Paramiko script is trying to connect to the wrong port.
Solution:
- Verify Port: Confirm the SSH port on the remote server (often found in
/etc/ssh/sshd_configasPort 22, or a custom value). - Specify Port in Paramiko: Ensure you’re passing the correct port to
client.connect().client.connect(hostname='...', port=2222, ...) # Example for custom port 2222 - Telnet/Netcat: Use telnet or nc from your client to test if the port is open and listening.
telnet your_server_ip 22 nc -vz your_server_ip 22 # For netcatIf it hangs or gives “Connection refused,” the port is likely blocked or not listening.
3. Firewall Blocking Connection (Client or Server Side)
Cause: A firewall (on your client machine, the remote server, or an intermediate network device) is blocking the SSH connection.
Solution:
- Client Firewall: Check your local machine’s firewall (e.g., Windows Defender Firewall, ufw on Linux, macOS Firewall) to ensure it’s not blocking outgoing SSH connections.
- Server Firewall: This is a very common cause. Check the remote server’s firewall (ufw, firewalld, iptables) and any cloud provider security groups (e.g., AWS Security Groups, Azure Network Security Groups, Google Cloud Firewall Rules) to ensure incoming connections on the SSH port are allowed from your client’s IP address.
# On server (example for ufw) sudo ufw status sudo ufw allow ssh # or sudo ufw allow 22/tcp
4. SSH Server Not Running or Crashed
Cause: The SSH daemon (sshd) on the remote server might not be running, or it might have crashed.
Solution:
- Verify Server Status: If you have console access or another way to connect, check the SSH service status on the remote server.
sudo systemctl status sshd # For systemd-based systems (most modern Linux) sudo service sshd status # For older init systems - Start/Restart SSH Service: If it’s not running, try starting it.
sudo systemctl start sshd sudo systemctl restart sshd # To restart
5. Network Routing Issues
Cause: There might be a problem with network routing between your client and the server, preventing packets from reaching their destination.
Solution:
- Traceroute/Tracert: Use traceroute (Linux/macOS) or tracert (Windows) to see the network path and identify where the connection is failing.
traceroute your_server_ip_or_hostname - Network Configuration: Consult with your network administrator if you suspect routing issues in a complex network environment.
6. Connection Timeouts
Cause: The network connection is very slow, or the server is under heavy load, causing the connection attempt to time out before a successful handshake can occur.
Solution:
- Increase Timeout: Increase the timeout parameter in client.connect().
client.connect(hostname='...', timeout=30) # Try a higher timeout, e.g., 30 seconds - Check Server Load: If you have access, check the remote server’s CPU, memory, and network utilization.