Hypervisor License Expired Fix: Get VMs Running

Your hypervisor license expired. I get it—it's a pain when your VMs just sit there.

Last month, a client called me frantic because their ESXi host wouldn’t start any VMs. The error screen said Hypervisor License Expired. They’d been running a trial for months and forgot to renew. Here’s how I fixed it in under 10 minutes.

The Quick Fix: Rearm the Trial

If you’re still in the evaluation period (usually 60-90 days) and just hit the expiry, you can reset the trial clock. Most hypervisors let you rearm once. Here’s how for the big two:

For VMware ESXi 6.x and 7.x

SSH into the ESXi host or use the DCUI (Direct Console UI).
Run this command to check current license state:
```
esxcli system license list
```
If expired, reset the trial with:
```
esxcli system license reset
```
Reboot the host. Not optional—VMs won’t start without a fresh boot after reset.

Why it works: The reset command clears the license timer and puts the host back into evaluation mode. VMware lets you rearm once. After that, you’ll need a real license key.

For Microsoft Hyper-V (Windows Server)

Hyper-V itself doesn’t have its own license—it’s part of Windows Server. If your Windows license expired, the hypervisor stops. Here’s the quick fix:

Open PowerShell as Administrator.
Run slmgr.vbs /rearm to reset the activation timer.
Restart the server (that’s a must for the rearm to stick).

Why it works: slmgr.vbs /rearm gives you 30 more days to activate. You can do this up to 5 times on most editions. After that, you’re stuck with a real license.

What If Rearm Doesn’t Work?

Sometimes the rearm fails—especially if you already used it. I’ve seen this happen when a client’s trial ran out and they tried to reset twice on ESXi. No dice. Here’s the backup plan:

Apply a New License Key

For ESXi, use the vSphere Client or CLI. If you have a valid key, run:

esxcli system license set --license-key=XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

Replace the X’s with your key. Then reboot. For Hyper-V, you’d activate Windows Server normally—go to Settings > Activation and enter your product key.

Use a Free Edition (If You Can)

VMware ESXi free edition is a thing. It’s limited (no vSphere features, 8 vCPUs per VM max), but it’ll get you running. You can switch to it by entering a free license key from VMware’s site. Hyper-V is free on Windows Server, but the OS itself needs a license.

Less Common Variations

These pop up less often, but I’ve run into them:

License expired on a cluster (vSphere): If one host in a cluster expires, it can take down the whole DRS thing. Check each host individually with esxcli system license list. Apply the key to the host, not the cluster.
Evaluation period ended mid-migration: Had a client whose vMotion failed because the destination host’s license lapsed. Solution: boot the destination host with a fresh trial key, migrate the VMs, then fix the license later.
Hyper-V on Windows Server Core: Same fix—slmgr.vbs /rearm works fine. But if the server is domain-joined and KMS is down, you might need to restart the KMS service on the domain controller. That’s a different story.

How to Prevent This Going Forward

Don’t rely on memory. Set a calendar reminder 30 days before license expiry. I use a simple cron job on my management server that emails me weekly if the license is near expiry. Here’s a simple script for ESXi:

esxcli system license list | grep 'Expires' | awk '{print $3}'

Put that in a cron job that runs daily and alerts you if the date is within 30 days. For Hyper-V, you can check slmgr.vbs /dli in a scheduled task.

Also, if you’re running a production environment, buy a proper license. Trials are for testing, not for keeping your business running. My rule: never let a trial run past 45 days. You’ll thank yourself when the inevitable panic call doesn’t come.

Final Thought

License expiry is one of those problems that feels bigger than it is. The fix is simple: rearm or apply a new key, then reboot. Don’t overthink it. And please, set that reminder. I hate getting those calls at 2 AM.