Resolving duplicate serial numbers for macOS Virtual Machines.

Some Virtual Machines will use the serial number of the host computer as the VM serial number. This causes an issue with Watchman Monitoring, which will report the VM as a duplicate record. Modifying the serial number with the steps detailed below will eliminate the duplicate computer record and prompting in your Watchman Monitoring Dashboard.

Partially modifying your serial number may result in a valid serial number for AppleCare warranty lookups that will generate an Expiration in your Watchman Monitoring Dashboard.

Change the Serial Number


Parallels icon

Control-click (right-click) on the virtual machine and select Configure…

Parallels Virtual Machine > Configure...

Navigate to Hardware > Boot Order > Advanced settings.

Virtual Machine Configuration: Hardware > Boot Order > Advanced Settings

In Boot flags insert the following:

Boot flags

Boot flags is available only in Parallels Desktop Pro and Parallels Desktop Business editions

vmware Fusion

Control-option-click (hold Option and right-click) on the virtual machine and select Show Config File in Finder.

vmware Fusion: VM Library > Show Config File

Edit the .vmx file by adding the following line at the end:

serialNumber = SERIALNUMBER

Virtual Box

In Terminal run the following command substituting the name of your VirtualBox virtual machine and your serial number (all one line):

VBoxManage setextradata “YOURVMNAME” VBoxInternal/Devices/efi/0/Config/DmiSystemSerial “SERIALNUMBER“

Retrieve Serial Number


system_profiler SPHardwareDataType | awk '/Serial Number/ { print $4 }'


wmic bios get serialnumber


dmidecode -s system-serial-number

Understanding Apple’s Serial Number

Apple has two series of Serial Numbers. An 11-character format used up until 2010, and a 12-character format that is currently in use.



PP or PPP – Plant Code (Manufacturing Location)

Y – Year of Manufacturing

W or WW – Week of Manufacturing

UUU – Unique Identifier

CCC or CCCC – Model Number


Year – In the old format, this was the last digit of the year. In the new format, Apple uses 20 letters, omitting vowels A, E, I, O, and U, as well as B. Letters will recycle every ten years. For 2010, machines with “C” in this position have been manufactured in weeks 1-26, while machines with a “D” will have been manufactured in weeks 27-52 or 53.

Week – In the old format, this was 01-53. In the new format, Apple uses 27 alphanumeric characters to denote the week of manufacture, starting with 1-9, then C through Y (omitting 0, vowels A, E, I, O, and U, as well as B, S, and Z). The “W” week must be paired with the “Y” year code to determine whether the machine was manufactured in the first or second half of the year, with the “W” codes being recycled every six months.



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