An OMV server running OMV 3 (Erasmus) may experience a loss of wifi (wlan0) due to drivers being removed from the backports package.
Run the code below to download the broadcom wifi controller drivers and re-enable wifi (wlan0) (from OMV forums)
|sudo mv brcmfmac43430-sdio* /lib/firmware/brcm/|
Consequently, this is also a good time to learn about wireless network troubleshooting tools:
ifconfig -a iwconfig sudo iwlist wlan0 scan sudo ifdown wlan0 && sudo ifup -v wlan0
If any of these show an error or do not show the wlan0 interface, you may have a driver issue, such as the one with OMV and the RPi3 backport repository.