@Galgani, Stefano Welcome to Microsoft Q&A, Thank you for posting your here!!
When you enable System Assigned Managed Service Identity for your Linux VM it creates a Service Principal (visible under Enterprise applications in Azure Portal).
Even though you can only see the Object ID in Identity blade on Linux VM, but you can find a few more details including Application ID (or Client ID as you ask) by going to Azure Portal > Azure Active Directory > Enterprise Applications > All Applications > Relevant Service Principal (you can figure out using display name which is same as your Linux VM or the Object ID). More detailed steps along with screenshots below.
Please note that even though you can get to Application ID and some details for MSI, you will not find an actual app registration for it.
- For example, I have an VM named "Test1" as shown here
- Go to Azure Portal > Azure Active Directory > Enterprise Applications > All Applications
- Go to the properties of Service Principal for more details.
Hope this helps!
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