Like any real computer, Qemu attributes a UUID to the system. This is stored in the SMBIOS:
Most of the time, you won’t need to set a UUID yourself. However this information could be used by vendors (for example), to check for a valid licence.
A UUID is generated by default for each node included in a project. This UUID is kept across machine reboots.
To force a UUID, you will have to pass the
-uuid option to the Qemu command line. This can be set in the advanced settings tab, when editing a nodes global configuration: