Table of Contents
Problem Statement
The VM in Google Cloud Platform (GCP) is inaccessible over SSH, preventing normal administrative operations. This issue is likely caused by SSH key misconfigurations, firewall rule misalignments, or corruption of critical system files.
Solution Overview
The recommended solution is to enable serial console login to directly access the VM. This method bypasses SSH and relies on the serial console feature provided by GCP to troubleshoot and fix issues.
Step-by-Step Solution
Enabling Serial Console Login
Enable Serial Console Access
Navigate to the Google Cloud Console.
Go to VM Instances under the Compute Engine section.
Select the affected VM.
Click on Edit and ensure the Enable serial port checkbox is selected.
Save the changes.
Connect to Serial Console
Open the serial console by selecting the "Connect to serial console" option from the VM instance page in the GCP console.
Log in to the VM
Use a root user or any pre-configured credentials. If login fails, reset the password or create a new user in GCP metadata.
Diagnosing and Resolving Issues
Check SSH Configuration Files
Verify sshd_config for misconfigurations:
sudo nano /etc/ssh/sshd_config
Ensure PermitRootLogin and PasswordAuthentication are correctly set:
PermitRootLogin yes PasswordAuthentication yes
Restart SSH ServiceRestart the SSH service to apply changes:
sudo systemctl restart sshd
Verify Disk Space and System Logs
Check if disk space issues are preventing SSH operations:
df -h
Analyze logs for SSH errors:
sudo tail -f /var/log/auth.log
Update SSH Keys in Metadata
In the GCP console, navigate to Metadata > SSH Keys.
Add a new key or update an existing one.
Reboot the VMReboot to ensure changes take effect:
sudo reboot
Alternate Solutions
Verify and Update Firewall Rules
Go to VPC Network > Firewall Rules in the GCP console.
Ensure a rule exists to allow SSH traffic on port 22 from your IP address or a valid range.
Add or Update SSH Keys
Use the Google Cloud SDK (gcloud) to update SSH keys:
gcloud compute ssh --zone=<zone> <instance-name> --ssh-key-file=<key-file>
Use the VM Repair Tool
Use GCP's VM Repair Tool to reset SSH settings or recover the VM:
gcloud compute instances repair <instance-name> --zone=<zone>
Conclusion
Enabling serial console access is the most direct and reliable method for troubleshooting SSH connectivity issues in GCP. It allows access to the VM regardless of network or SSH configurations. Alternate solutions, such as fixing firewall rules or updating SSH keys, provide additional ways to restore connectivity.
Would you like assistance with configuring automated recovery for SSH issues?
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