Question: Restarting SyncServices
This is more of an FYI, in case somebody else has the same problem I did. My SugarSync desktop app kept crashing, and I eventually discovered via a file in $HOME/Library/Logs/DiagnosticReports that it was because of FinderSyncExt.
Look at the file '$HOME/Library/Logs/Sync/syncservices.log'. You will likely see messages that contain:
"Can't upgrade SyncServices data schema in directory”. If you see this, you will need to get a clean copy of the directory: '$HOME/Library/Application\ Support/SyncServices/Local/'
followed by a really specific procedure using the terminal.
I'm not super comfortable with the terminal, so I decided to try a simpler option first. First, I uninstalled SugarSync. Then on another Mac logged into the same iTunes account, I navigated to $HOME/Library/Application Support/ and created a zip file of SyncServices. I copied the zipfile to $HOME/Library/Application Support/ on the Mac that wouldn't sync. Then I renamed the original folder to SyncServices-old and replaced it with the unzipped folder. When I reinstalled SugarSync after that, it started right up.
If you have the same sort of problem, maybe this can help.
p.s. For some reason this is in the OS X El Capitan community, but I have High Sierra.
iMac with Retina 5K display, macOS High Sierra (10.13.3), null