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Veeam Plug-In for Microsoft Azure Appliance Service Fails to Start After .NET Update with "System.IO.IOException: The system cannot open the device or file specified" Error

KB ID: 4947
Product: Veeam Plug-In for Microsoft Azure | 8
Published: 2026-10-19
Last Modified: 2026-10-19
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Challenge

After installing pending operating system updates on the Veeam Plug-In for Microsoft Azure appliance, the update process fails during finalization and the appliance web UI becomes unavailable. The Veeam Azure Backup service starts and then stops with exit code 255, and the following error is logged in the appliance syslog:

System.IO.IOException: The system cannot open the device or file specified. : 'Global\9EA74B1E'
   at System.Threading.Mutex.CreateMutexCore(Boolean initiallyOwned, String name, Boolean& createdNew)
   at System.Threading.Mutex..ctor(Boolean initiallyOwned, String name)

This issue affects appliances running version 8 or later.

Solution

To resolve this issue, change the owner of the .NET directory on the appliance and restart it:

  1. Log in to the Veeam Plug-In for Microsoft Azure appliance via SSH (use the same credentials as for the web UI).
  2. Change the ownership of the /home/veeamazure/.dotnet directory and all its contents by running the following command:
sudo chown -R veeamazure:veeamazure /home/veeamazure/.dotnet
  1. Reboot the appliance by running the following command:
sudo reboot

More Information

As an alternative to changing the ownership of the .NET directory, the .NET 8 runtime packages can be downgraded to version 8.0.31:

  1. Log in to the Veeam Plug-In for Microsoft Azure appliance via SSH (use the same credentials as for the web UI).
  2. Check the installed .NET version by running the following command:
dotnet --list-runtimes
  1. Downgrade the .NET 8 runtime packages to version 8.0.31 by running the following command:
sudo apt-get install --allow-downgrades aspnetcore-runtime-8.0=8.0.31-1 dotnet-runtime-8.0=8.0.31-1 dotnet-hostfxr-8.0=8.0.31-1 dotnet-host=8.0.31-1
  1. Reboot the appliance by running the following command:
sudo reboot

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