Fenix 3 “manual” firmware install
Normally the Fenix 3 firmware is updated via Garmin Express, so Linux users have to update otherwise.
Obtain the image you need from this repository.
Check for duplicate headers and remove if necessary: The header starts with “KpGrd” and contains a date and timestamp, it is 60 bytes long.
od -c [downloadedFWfile] |head
If you see it twice, remove it:
tail –bytes=+61 [downloadedFWfile] > [newFWfile]
Check with od that the header is now single.
Rename the [newFWfile] to GUPDATE.RGN
Put it on the USB filesystem of the Fenix 3 in \Garmin.
Wait for writing to finish, unmount Fenix 3, and it will prompt to install the update.
You can always upgrade versions without losing any information, but going back versions will always reset the watch to factory defaults.