3 restarts for 10.13.6 security update
I just installed the High Sierra security update. The file was 1.88GB and took less than 2 minutes to download.
I clicked restart and the installer restarted my mini and started doing it's thing. Soon the progress bar got about a third of the way to complete and then suddenly reversed to about 1 tenth done, then restarted. Again the progress bar advanced some and then drew back again and then restarted for the third time. Soon a dialogue box under the progress bar told me about 45 minutes remaining. When it hit 40 minutes remaining it recalculated and said 47 minutes remaining. I watched it go down to 41 minutes remaining before I decided I better get the lawn mowed. I finished the lawn in about a half hour and came back to have the mini up and running with the App store open (with MS Office at the top of the page).
I am getting old but I seem to remember when the double start up upon upgrading first happened people were thinking something's wrong. No question just some rambling.