Azure VM Boot Issue – VM stuck in ‘Starting’ or ‘Failed’

calendar Aug 3, 2025 · 3 min read · Azure VM Troubleshooting Boot diagnostics Serial Console NSG Repair  ·
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Azure VM Boot Issue – VM stuck in ‘Starting’ or ‘Failed’

You hit Start on your Azure VM… and it gets stuck in:

“Starting…”
“Provisioning failed”
“Failed to start VM”

You’re not alone — this is a common issue. In this blog, I’ll show you how to troubleshoot and fix it using step-by-step, beginner-friendly methods.

Common Causes

Problem Example
Corrupt OS disk Kernel panic / bluescreen
VM extension failed “Failed to install extension”
NSG or route blocking Boot agent No serial output
DNS or DHCP misconfigured Stuck boot or network unreachable
OS-level login or update hang Incomplete patch

Step-by-step Fix Guide

Step 1: Open Boot Diagnostics

Go to your VM → Boot diagnostics

  • Check Screenshot tab
    • Windows: Blue screen? Login screen?
    • Linux: Kernel panic? Black screen?
  • Check Serial log
    • Look for errors: Failed to mount, No bootable disk, etc.

This is your first clue into what went wrong.

Step 2: Try Serial Console (If OS boots partially)

VM → Serial Console

  • Windows:
    • Login with credentials
    • Check sconfig or Event logs
  • Linux:
    • Use root shell
    • Check /var/log/syslog or dmesg
journalctl -xe
systemctl status

You can fix fstab, services, or disable broken extensions directly.

Step 3: Run “Redeploy VM”

Go to VM → Support + Troubleshooting → Redeploy This:

  • Moves your VM to another host
  • Retains public/private IP and disk
  • Fixes hypervisor-side issues
  • Works well for random “Failed to start” errors.

Step 4: Reset SSH or RDP Access (if login fails)

VM → Reset password → Choose OS → Reset login

VM → Run Command → Reset SSH config (Linux)

az vm user update --name vm1 --resource-group myRG \
  --username azureuser --password 'StrongP@ssword123!'

Step 5: Disk Repair (Advanced)

  • Stop VM
  • Detach OS disk
  • Attach to a healthy rescue VM
  • Mount and inspect disk:
sudo fdisk -l
sudo mount /dev/sdc1 /mnt
Fix /etc/fstab, remove bad init files, update kernel

Reattach disk to original VM and boot

Step 6: Check NSG or Route Table

Ensure outbound access to: Azure platform IPs (168.63.129.16) DNS (8.8.8.8 or 168.63.129.16) If UDRs block outbound or Boot diagnostics, VM won’t load properly

Summary Table

Fix Use When
Boot diagnostics screenshot See if OS booted
Serial Console Fix login or boot issues
Redeploy VM Platform/infrastructure issues
Reset SSH/RDP Login or key problems
Disk Repair via Rescue VM Corrupt boot or config file
NSG/UDR fix Connectivity / agent failures

Pro Tips

  • Always enable Boot Diagnostics for all VMs
  • Take snapshot before running updates
  • Use custom script extension to auto repair
  • Use Availability Set or Zone to avoid platform issues

Resources

  • Azure VM Serial Console
  • Redeploy VM guide
  • Run command from portal
  • Facing the boot error right now?

Message me on LinkedIn for a walkthrough.

– Kasi @ KasdevTech