Turned an old WatchGuard XTM 5 into an OPNsense firewall… after way more BIOS pain than expected
Picked up an old WatchGuard XTM 5 and thought it would be a quick win — throw in an SSD, install OPNsense, done.
Yeah… not quite.
Started off simple:
- Swap out the tiny CF card
- Add RAM
- Install OPNsense to SSD
Then everything went sideways.
As soon as SATA was connected → no boot.
Tried multiple drives → same issue.
Turned out the real problem was the locked-down BIOS and some very outdated assumptions baked into the hardware.
Ended up:
- Flashing an unlocked BIOS
- Switching SATA to AHCI
- Reinstalling OPNsense using MBR instead of GPT
- Manually fixing boot/root issues
After all that, it finally clicked.
Now it:
- Boots cleanly from SSD
- Updates properly
- Runs OPNsense without any weird hacks
- Lives in the rack as a proper firewall
Honestly went from “this will take an hour” to “why do I do this to myself” real fast 😅