UniFi USW-Flex Vanishing or Not Adopting Fix

UniFi USW-Flex switches that adopt and then vanish off the network — or refuse to adopt at all — are almost always running a bad firmware build. Upgrading over SSH before adoption fixes it.

The symptoms

• The switch adopts, then disappears from the network shortly afterwards.
• The switch will not adopt at all, or the adoption fails part-way through.

There appears to be a bad batch of firmware on many Flex switches that causes exactly this behaviour. The fix is to push the current firmware onto the device manually over SSH, then adopt it.

The fix, step by step

1. Find the latest USW-Flex firmware

   Go to https://www.ui.com/download/software/usw-flex and save the direct download link to a text file. It will look something like:

   https://dl.ui.com/unifi/firmware/USF5P/7.1.26.15869/US.mt7621_7.1.26+15869.240926.1436.bin

2. Open an SSH session

   Open PuTTY, put the IP address of the Flex switch in, and connect. Check your device client list or run a network scan if you don't know the IP.

3. Log in

   If the switch has never been adopted, the credentials are the defaults — username ubnt, password ubnt. If you have previously adopted it, use the credentials shown in your admin panel under Settings >> System >> Advanced >> Device Authentication.

4. Push the firmware

   Run upgrade followed by the firmware URL you saved. Replace the example below with the latest link from the UniFi firmware download page.

upgrade https://dl.ui.com/unifi/firmware/USF5P/7.1.26.15869/US.mt7621_7.1.26+15869.240926.1436.bin

1. Wait for the reboot

   The device reboots on its own and takes a few minutes to come back online.

2. Reconnect over SSH

   Open a duplicate PuTTY session to the same IP address.

3. Point it at your controller

   Run the set-inform command with your own controller address in place of the example.

4. Adopt it

   Accept the new device on the UniFi controller. Sometimes you need to check the phone app to complete the adoption.

set-inform http://myunificontrollerdomain.com:8080/inform

Still not working?

Reset the device back to factory defaults. Type the following into the SSH session — it does include the trailing & symbol:

syswrapper.sh restore-default & set-default &

Give it a few minutes after running the command. You should then be able to log back in over SSH with the default ubnt/ubnt credentials.

Run the set-inform command once more and the switch should appear in the controller's device list as ready for adoption.