The older USG-3P can sometimes have a major failure, which will require you to reinstall the base operating system from scratch. Like early examples of EdgeRouters, the USG uses a USB drive to run its OS from and this is the main culprit for the device failing.
As of 2022, the older USG is no longer a recommendation of ours. Going forward, we would recommend the UXG Pro, it is the same size as the USG 4P, but is practically silent to run. It has the same specs as the UDM Pro and is powerful enough to power most home and business networks, plus it can be adopted to HostiFi UniFi controllers.
Before we get into how to repair the drive on the USG, we need to look at what the main symptoms are. First of all, if your USG regularly goes offline within UniFi and needs a physical power cycle to get working again, then this guide is for you.
Other things that might happen is the USG will still work for existing clients who already have a DHCP lease, but any new devices won't be able to get online.
The main issue with the USG-3P is the USB drive it has inside. This gets corrupted and needs reformatting and having the USG operating system reinstalling on it. Thankfully, Ubiquiti still offers this OS for download and the process is relatively easy to do.
Taking the USG apart
To get access to the USB drive, we need to unscrew the back plate of the USG. The screws are located underneath these four sticky pads. Carefully remove them with your fingernails, or a flat blade screwdriver.
Once removed, use a Phillips #1 (PH1) screwdriver to remove the screws and pull the bottom case towards you.
Once removed, flip it over and you'll be able to see the main motherboard for the USG. Circled in red is the USB drive in question.
Chris Buechler, from Ubiquiti posted very loose instructions of this process and has also posted the original firmware file the USG would have shipped with initially. 4.2.0 is available from the link below.
Unzip and dd
First thing we need to do is unzip the download firmware file. The file comes as a compressed bz2 file. On most operating system, just opening up a compressed file will uncompress it.
The firmware file is 4.02GB in size and will now need imaging onto the USB drive so we can use the USG again. On Windows, use something like Win32diskimager to complete this and on macOS, the included Disk Utility with macOS will work too.
Install USB back into USG
Once the USB drive is formatted correctly, reverse the first steps to get the USG reassembled.
Because the base firmware is 4.2.0, it won't be possible to adopt the USG into UniFi now until it is updated.
Instead, plug the USG WAN into a network offering DHCP and then plug your computer into the LAN port. Using our SSH guide, upgrade the firmware to the latest version.
Adopt into UniFi
Finally, once the USG firmware is updated, adopt the USG into your UniFi controller.
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