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Fix Azure VM Extension Failed

Resolve Azure VM extension failures by checking extension status, reviewing logs, and reinstalling extensions with correct settings.

Published: Apr 3, 20267 min readBy FixWikiHub Editorial Team

Abstract illustration for a troubleshooting knowledge base category.

Introduction

Azure VM extensions provide post-deployment configuration, monitoring, and security capabilities. When extensions fail, VMs may lack required configurations, monitoring agents, or security tools, affecting operations and compliance.

Symptoms

Extension provisioning failed:

```bash $ az vm extension list \ --vm-name my-vm \ --resource-group my-rg \ --query "[?provisioningState=='Failed'].{Name:name,State:provisioningState,Message:instanceView.statuses[0].message}"

# Shows extension in failed state ```

Extension timeout:

json

{
  "status": "error",
  "message": "Extension installation timed out after 900 seconds"
}

Dependency error:

json

{
  "code": "ExtensionDependencyFailure",
  "message": "Extension 'Microsoft.Compute.CustomScriptExtension' depends on 'VMAccessExtension' which failed"
}

Common Causes

1.Extension script error - Custom script has syntax or runtime errors
2.Network connectivity - Extension can't reach required resources
3.VM agent not running - Guest agent offline or unhealthy
4.Settings misconfiguration - Invalid extension settings
5.Timeout exceeded - Extension takes too long to complete
6.Resource not found - Referenced storage account or file missing
7.Permission denied - Extension lacks required permissions

Step-by-Step Fix

Step 1: Check Extension Status

```bash # List all extensions on VM az vm extension list \ --vm-name my-vm \ --resource-group my-rg \ --query '[].{Name:name,State:provisioningState,Version:typeHandlerVersion}'

# Get detailed extension status az vm extension show \ --vm-name my-vm \ --resource-group my-rg \ --name CustomScriptExtension \ --query '{State:provisioningState,Status:instanceView.statuses}' ```

Step 2: Check VM Agent Status

bash # Check VM agent status az vm get-instance-view \ --name my-vm \ --resource-group my-rg \ --query 'instanceView.extensions[?name==VMAgent`].statuses'

# If agent not running, restart it # Linux: sudo systemctl restart waagent

# Windows: net stop WindowsAzureGuestAgent net start WindowsAzureGuestAgent ```

Step 3: View Extension Logs

```bash # Linux extension logs # SSH to VM: ls -la /var/log/azure/ cat /var/log/azure/custom-script/handler.log

# Windows extension logs # RDP to VM: # C:\WindowsAzure\Logs\Plugins\Microsoft.Compute.CustomScriptExtension\ ```

Step 4: Check Extension Settings

```bash # View extension settings az vm extension show \ --vm-name my-vm \ --resource-group my-rg \ --name CustomScriptExtension \ --query 'settings'

# Common issues: # - Invalid fileUris # - Missing commandToExecute # - Invalid storage account access ```

Step 5: Reinstall Extension

```bash # Remove failed extension az vm extension delete \ --vm-name my-vm \ --resource-group my-rg \ --name CustomScriptExtension

# Reinstall with correct settings az vm extension set \ --vm-name my-vm \ --resource-group my-rg \ --name CustomScriptExtension \ --publisher Microsoft.Compute \ --version 1.10 \ --settings '{"fileUris":["https://mystorage.blob.core.windows.net/scripts/script.sh"],"commandToExecute":"sh script.sh"}' ```

Step 6: Fix Network Connectivity

bash # If extension can't reach storage or download files # Check NSG rules allow outbound HTTPS az network nsg show \ --name my-nsg \ --resource-group my-rg \ --query 'securityRules[?direction==Outbound`]'

# Add outbound rule if needed az network nsg rule create \ --nsg-name my-nsg \ --resource-group my-rg \ --name AllowHTTPS \ --direction Outbound \ --priority 100 \ --source-address-prefixes '*' \ --destination-port-ranges 443 \ --protocol Tcp \ --access Allow ```

Step 7: Use Managed Identity for Storage

```bash # Enable managed identity on VM az vm identity assign \ --name my-vm \ --resource-group my-rg

# Grant storage permissions VM_PRINCIPAL_ID=$(az vm show --name my-vm --resource-group my-rg --query identity.principalId -o tsv)

az role assignment create \ --assignee $VM_PRINCIPAL_ID \ --role "Storage Blob Data Reader" \ --scope /subscriptions/SUB/resourceGroups/my-rg/providers/Microsoft.Storage/storageAccounts/mystorage

# Use managed identity in extension az vm extension set \ --vm-name my-vm \ --resource-group my-rg \ --name CustomScriptExtension \ --publisher Microsoft.Compute \ --protected-settings '{"managedIdentity":{"clientId":"CLIENT_ID"}}' ```

Step 8: Increase Extension Timeout

```bash # For long-running scripts, increase timeout az vm extension set \ --vm-name my-vm \ --resource-group my-rg \ --name CustomScriptExtension \ --publisher Microsoft.Compute \ --settings '{"commandToExecute":"sh long-script.sh"}' \ --no-auto-upgrade true

# Default timeout: 90 minutes # Can be extended by using async execution in script ```

Step 9: Debug Custom Script

```bash # Run script manually to debug # SSH to VM: sudo sh /var/lib/waagent/custom-script/download/script.sh

# Check script syntax bash -n script.sh

# Run with verbose output bash -x script.sh ```

Step 10: Monitor Extension Health

```bash # Set up alert for extension failures az monitor metrics alert create \ --name vm-extension-failures \ --resource-group my-rg \ --scopes /subscriptions/SUB/resourceGroups/my-rg/providers/Microsoft.Compute/virtualMachines/my-vm \ --condition "count ExtensionStatus == 0 where ExtensionStatus == 'Failed'" \ --window-size 5m

# Check extension activity az monitor activity-log list \ --resource-group my-rg \ --resource Microsoft.Compute/virtualMachines/my-vm \ --query "[?contains(operationName.value, 'extension')].{Time:eventTimestamp,Operation:operationName,Status:status.value}" ```

Common Azure VM Extensions

Extension	Purpose	Common Errors
CustomScript	Run scripts	File not found, timeout
VMAccess	Reset password	Permission denied
AzureMonitor	Monitoring agent	Network blocked
AzureDiskEncryption	Encrypt disks	Key Vault access
DependencyAgent	Service mapping	VM agent down

Verification

```bash # After reinstalling extension az vm extension show \ --vm-name my-vm \ --resource-group my-rg \ --name CustomScriptExtension \ --query '{State:provisioningState,Status:instanceView.statuses[0].displayStatus}'

# Should show: # State: Succeeded # Status: Provisioning succeeded

# Check extension output az vm extension show \ --vm-name my-vm \ --resource-group my-rg \ --name CustomScriptExtension \ --query 'instanceView.substatuses' ```

Prevention

To prevent Azure VM extension failed issues from recurring, implement these proactive measures:

1. Monitor Extension Health

yaml

groups:
- name: azure-vm-extensions
  rules:
  - alert: AzureVMExtensionFailed
    expr: |
      azure_vm_extension_provisioning_state != "Succeeded"
    for: 5m
    labels:
      severity: warning
    annotations:
      summary: "Azure VM extension provisioning failed"

2. Test Extension Deployment

```bash # Test extension in staging VM first az vm extension set \ --vm-name test-vm \ --resource-group staging-rg \ --name CustomScriptExtension \ --publisher Microsoft.Compute \ --version 2.1 \ --settings '{"fileUris":["https://test.blob.core.windows.net/scripts/test.sh"]}' \ --protected-settings '{"commandToExecute":"./test.sh"}'

# Verify success before production deployment ```

3. Maintain Extension Versions

```bash # Track extension versions az vm extension image list \ --publisher Microsoft.Compute \ --name CustomScriptExtension \ --query '[].{Version:version,Date:date}' -o table

# Use stable versions, avoid latest in production az vm extension set \ --vm-name my-vm \ --resource-group my-rg \ --name CustomScriptExtension \ --publisher Microsoft.Compute \ --version 2.1 # Fixed version ```

Best Practices Checklist

[ ] Monitor extension health
[ ] Test extension in staging first
[ ] Use stable extension versions
[ ] Ensure VM agent is running
[ ] Check network connectivity
[ ] Document extension configurations

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Last updated: Apr 3, 2026

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Fix Azure VM Extension Failed

Introduction

Symptoms

Common Causes

Step-by-Step Fix

Step 1: Check Extension Status

Step 2: Check VM Agent Status

Step 3: View Extension Logs

Step 4: Check Extension Settings

Step 5: Reinstall Extension

Step 6: Fix Network Connectivity

Step 7: Use Managed Identity for Storage

Step 8: Increase Extension Timeout

Step 9: Debug Custom Script

Step 10: Monitor Extension Health

Common Azure VM Extensions

Verification

Prevention

1. Monitor Extension Health

2. Test Extension Deployment

3. Maintain Extension Versions

Best Practices Checklist

People also search for

Browse Guides from Other Categories

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DNS

Azure Troubleshooting FAQs

FixWikiHub Editorial Team

Disclaimer & Safety Guidelines

Official Documentation & Further Reading

Fix Azure VM Extension Failed

Introduction

Symptoms

Common Causes

Step-by-Step Fix

Step 1: Check Extension Status

Step 2: Check VM Agent Status

Step 3: View Extension Logs

Step 4: Check Extension Settings

Step 5: Reinstall Extension

Step 6: Fix Network Connectivity

Step 7: Use Managed Identity for Storage

Step 8: Increase Extension Timeout

Step 9: Debug Custom Script

Step 10: Monitor Extension Health

Common Azure VM Extensions

Verification

Prevention

1. Monitor Extension Health

2. Test Extension Deployment

3. Maintain Extension Versions

Best Practices Checklist

Related Issues

Related Articles

People also search for

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