Qemu system UUID
Like any real computer, Qemu attributes an UUID to the system. This is stored in the SMBIOS:
Most of the time you won’t need to set an UUID yourself, however this information could be used by manufacturers, for instance, to check for a licence.
An UUID is generated by default for each node included in a project. This UUID is kept across machine reboots.
To force an UUID, you will have to pass the -uuid option to the Qemu command line. This can be set in advanced settings.