Hi,
I just wanted to share how I solved this high-CPU-usage problem. The short story is: delete all your symbolic links from under the Dropbox folder.
Long story:
I'm on macOS High Sierra and I found that a system process ("daemon") called "opendirectoryd" keeps using 50--100% of CPU all the time as long as the computer is up. I don't know exactly when this started, but it started recently, say a few weeks.
I searched the Net and found a lot of discussions about the daemon using a lot of CPU time. Apparently there are so many different causes. Some of the discussions pointed to Dropbox.
I indeed found that Dropbox is the cause: when I pause syncing, the daemon's CPU use immediately drops well below 1% and as soon as I resume Dropbox syncing, the daemon's CPU use shots up and stays there forever.
But all the Dropbox-related answers say that you should delete dead symbolic links. I did delete the few dead symbolic links I had in my Dropbox folder but the problem persisted.
Then I came across this document in the Dropbox help:
https://www.dropbox.com/help/desktop-web/high-cpu-usage
which says that Dropbox uses a lot of CPU time to hand symbolic links (dead or not). Although I didn't want to do that, I bit the bullet and deleted all my symbolic links under the Dropbox folder and moved the files and folders from my main directory to Dropbox.
Now, the opendirectoryd daemon stays calm.
