The error "Junos version too old for VMHost" typically occurs when attempting to install or upgrade the VMHost software using the request system software add command. This process is invalid for VMHost upgrades, as the VMHost package requires the specific request vmhost software add command for installation.
This issue commonly arises when the installed Junos version is incompatible or outdated for the VMHost software being added.

Users may observe the following issues:

1. Error Message During Upgrade:
   When attempting to add a VMHost package with the incorrect command, the following error appears:

   Checking vmhost version compatibility 
   Junos version too old for VMHost
   ERROR: package vmhost-x86_64-22.2R3 fails requirements
   ERROR: Failed to add vmhost-x86_64-22.2R3.tgz
   

2. Upgrade Failure:
   The system halts the upgrade process, preventing the VMHost package from being installed.

3. Command Usage Mismatch:
   The request system software add command is used instead of the correct request vmhost software add command.

To resolve this issue, follow these steps:

1. Verify the Current Junos and VMHost Versions:

   • Run the following command to check the installed Junos and VMHost versions:
      

      

     show vmhost version
   • Confirm the compatibility between the installed Junos version and the target VMHost package using Juniper’s release notes or compatibility matrix.

2. Install the VMHost Package with the Correct Command:

   • Use the request vmhost software add command to install the VMHost package. For example:
      

      

     request vmhost software add /var/tmp/vmhost-x86_64-22.2R3.tgz
   • This command ensures the system recognizes the package as a VMHost software update.

3. Upgrade Junos to Match the Target VMHost Version (If Needed):

   • If the Junos version is too old for the required VMHost package, upgrade Junos to a compatible version before attempting to install the VMHost software.
   • Install the compatible Junos version using:
      

     request system software add /var/tmp/junos-install-mx-x86-64-22.3R1.tgz

4. Revalidate the Installation:

   • After successfully adding the VMHost package, confirm that the software versions are compatible by re-checking the VMHost version:
      

     show vmhost version

5. Best Practices:

   • Always refer to Juniper documentation for the recommended upgrade paths and compatibility requirements.
   • Use the request vmhost software add command exclusively for VMHost software upgrades.

By following the correct upgrade procedure and ensuring compatibility, you can avoid errors and achieve a successful VMHost software update.