I found the following post that has a very comprehensive list of UniFi commands.

All Unifi SSH Commands that You Want to Know

Some of the most common ones that are used

Reset a device

set-default

or

syswrapper.sh restore-default

Reboot a device

reboot

Connect device to a controller

After you run this command, adopt it in the controller and then run the command again.

set-inform http://ip-of-controller:8080/inform

Also note that the above command does not seem to work over https.