Three years of flawless operation, and then, out of nowhere: Adoption Failed. 😤 No firmware update, no cable changes, nothing had been touched. The U6 Lite just stopped working overnight. I checked the cable, tried a reboot, ran the usual rounds of Google searches. Nothing helped. Then I noticed that the IP the controller listed for this AP was pointing to something very suspicious.
UniFi Adoption Failed on UDM Pro is often caused by a stale IP cached in the controller, so it SSH-es into itself instead of the AP. Fix: find the AP's real IP, SSH in, run set-inform, done.
The Problem: Adoption Failed on the U6 Lite 🤔
My setup runs on a UDM Pro as both gateway and controller. Five APs in the house, all UniFi, everything working fine for years. The U6 Lite had been running without a single hiccup for three years, until one morning it simply didn't anymore. No warning signs, no gradual degradation. Just: Adoption Failed.
What tipped me off: when I opened the IP address the controller was showing for that AP in my browser, I landed on the UDM Pro's hotspot portal, at 192.168.1.1. The controller was essentially trying to adopt itself. That's not going to work. 😅
The Root Cause: The Controller Has the Wrong IP 🕵️
Here's what's happening under the hood:
UniFi devices get their IP addresses via DHCP in most home networks. That means every time an AP reboots or its DHCP lease expires, it may end up with a different IP. If the controller still has the old IP cached, it sends the SSH adoption request to the wrong place, or in my case, to itself.
This is the part none of the usual guides cover: in a UDM Pro setup, the controller's own management IP is 192.168.1.1. When the AP's cached IP happened to be that same address, the adoption attempt hit the UDM Pro's own interface, got rejected, and showed Adoption Failed. The AP itself was completely fine.
Note: This is not a hardware defect. The AP is perfectly functional. The issue is entirely that the controller doesn't know where the AP actually is on the network.
Step 1: Find the AP's Real IP Address 🔍
Before touching anything via SSH, we need the AP's actual current IP, not whatever the controller thinks it is.
Option A: UDM Pro DHCP Lease Table
In the UDM Pro under Settings → Networks → LAN, there's a DHCP client list. Find the AP by hostname (usually U6-Lite) or by the MAC address printed on the device.
Option B: UniFi Network App In the mobile app under Clients, the AP often shows up as an unknown client with its assigned IP right there.
Option C: ARP Table
On a Windows PC on the same network: run arp -a in PowerShell. The AP shows up as an unknown device you can identify by its MAC address.
Step 2: Get the SSH Password from the UniFi Controller 🔑
Ubiquiti moved the SSH password location in newer UniFi versions. It's no longer buried in the general system settings, you'll find it here:
Settings → Devices → Device SSH
Copy the current password from there. The username is ubnt by default (or your admin username if you changed it).
Don't have PuTTY? Grab the standalone .exe from the official site, no installer needed. Windows PowerShell also works with ssh ubnt@{IP} if you prefer.
Step 3: SSH Into the AP 💻
Now we connect directly to the AP, using the IP we found in Step 1, not the one from the controller. In PuTTY, enter the AP's IP, port 22, and connect.
After logging in, you'll see the UniFi prompt:
BZ.v6.6.62# This confirms you're on the right device. If you get something else, a web interface, a login that doesn't match, double-check your IP from Step 1.
Step 4: Run set-inform ✅
Here's the actual fix. One command tells the AP to reach out to the controller at its correct IP:
set-inform http://192.168.1.1:8080/informReplace 192.168.1.1 with your UDM Pro's or controller's actual IP. The device responds with:
Adoption request sent to 'http://192.168.1.1:8080/inform'.
Use the controller to complete the adopt process.Back in the UniFi dashboard: the AP now shows as Pending Adoption. Hit "Adopt", after 30–60 seconds it's online and fully provisioned. 🎉
Prevention: Set Up a Static DHCP Reservation 🛡️
This problem can come back the next time the AP's DHCP lease expires and it picks up a different IP. The clean solution: give all your UniFi devices a fixed IP via DHCP reservation.
Here's how in the UDM Pro:
- Open Settings → Networks → LAN
- Click Add Fixed IP under DHCP
- Enter the AP's MAC address (printed on the device and visible in the DHCP lease list)
- Assign the IP you want it to always have (e.g.
192.168.1.153) - Save, from the next DHCP renewal onwards, the AP always gets that IP
With this in place, the controller always knows exactly where to find the device and adoption issues like this simply can't happen.
FAQ ❓
Why does UniFi show Adoption Failed when the device is clearly on the network?
The most common reason is a stale or incorrect IP cached in the controller. The device is reachable, just not at the address the controller expects. Running set-inform directly on the AP bypasses that problem entirely, the AP proactively contacts the controller at the correct URL.
What exactly does the set-inform command do?
set-inform instructs the UniFi access point to actively reach out to the controller at the URL you specify. Normally the AP discovers the controller automatically via DNS (http://unifi:8080/inform). When that fails, because no matching DNS record exists, or the controller has a wrong IP cached, set-inform gives the AP the correct address directly.
Where is the SSH password in newer UniFi versions?
Ubiquiti moved it a while back. In current versions it lives under Settings → Devices → Device SSH. Older versions had it under System → Advanced.
Do I need to factory reset the AP first?
No, and that's the advantage of this approach. A factory reset is only needed if the AP was previously adopted by a different controller and not properly released. For a brand new device or one that simply never adopted, set-inform is all you need.
What if set-inform doesn't work?
Run the command a second time, sometimes the AP needs two attempts. If that still doesn't work, verify that port 8080 is reachable between the AP and the controller. As a last resort, a hardware factory reset (hold the reset button for 10 seconds until the LED flashes) clears everything and lets you start fresh.
Conclusion 🎯
Fixing UniFi Adoption Failed sounds like a deep networking rabbit hole, but it often isn't. In my case, the controller had a stale IP that happened to point at itself, and one SSH command resolved it in under two minutes.
Add a static DHCP reservation for all your UniFi devices and you'll make sure this never comes back. Et voilà. 🎉