Unifi adoption fails with "disconnected" message

Are you getting a "disconnected' message in the GUI for the Unifi controller when you attempt to adopt a node?  Here is something that may help.

There are any number of reasons why a node might fail adoption.

SSH into the node in question, and issue an "INFO" command.
This procedure may help if you get the status "Unable to resolve"

EXAMPLE:BZ.v3.9.19# info
Model:       UAP-AC-Pro-Gen2
Version:     3.9.19.8123
MAC Address: 80:a2:41:bf:1c
IP Address:  10.8.60.172
Hostname:    UBNT
Uptime:      646 seconds
Status:      Unable to resolve (http://unifi:8080/inform)
BZ.v3.9.19#

This error, the node can't resolve the domain name of  "unifi" Seems to be a factory name configured somewhere.  So lets make that name resolvable by putting it and the IP of your controller into the HOSTS table of the device.  This works for both APs and the UNIFI switches.

Do this:

SSH to the AP/device
add a host entry into /var/etc/hosts

IPofController      unifi

So the final might look similar to this.  In my example the controller ip is 10.1.100.101

BZ.v3.9.19# cat /var/etc/hosts
127.0.0.1       localhost.localdomain   localhost
10.1.100.101 unifi
BZ.v3.9.19#

Try sending another set-inform command from the AP in question and follow the adoption process again.  Hopefully this will resolve the problem for you.

Running the command INFO should result in a status message similar if successful status message:

Status:      Connected (http://10.1.100.101:8080/inform)