There are 3 users sharing this computer. If you restart they will be disconnected.

ChangeAgent wrote:

This is the message I get on my Mac mini blind server when I try to do a restart.  Sometimes it reads as much a 6.  How can I see who or what is connected there?  

I treid these tips (https://www.compsmag.com/how-to/see-what-users-are-connected-logged-in-to-mac/) but that only shows the Mac mini as user.  And I know that for one I am at that point logged in as I am using remote control.

Any tips?  

Why the restart?

https://support.apple.com/guide/mac-mini/use-mac-mini-as-a-server-apd05a94454f/mac

See if this list all registered users on you computer, from the Terminal.app copy & paste

dscl . list /Users | grep -v '_'

Usual causes are remote screen-sharing sessions, and fast user switching; that there are users connected.

It is also possible that there are file shares being offered and accessed.

If you need to restart, restart.

You’ll hear about it, if there are other people effected.

If you have printers or scanners or other devices connected (Apple TV ...), depending on the configuration they may be counted as a "user."

ChangeAgent wrote:

This is the message I get on my Mac mini blind server when I try to do a restart.  Sometimes it reads as much a 6.  How can I see who or what is connected there?  

macOS Server User Guide - Apple Support