This is likely to mess up some headless setups : raspberrypi.org have disabled SSH in Raspbian PIXEL .
I have headless Pi’s in use as RTL-SDR server and LoRaWan single channel gateway. One of those was unreachable after updating the OS.
The solution is “If you want to enable SSH, all you need to do is to put a file called ssh in the /boot/ directory.“. And with “/boot/ directory.” they mean the root of the SD card.
RTL-SDR is a Software Defined Radio using a cheap DVB-T receiver with a chip from Realtek (RTL).
It can tune to 868 MHz and show activity, which is really handy when you are debugging a LoRa node and need to figure out if it is actually transmitting anything.
I bought the receiver from van Dijken Electronica at their stand at the VERON fleamarket for about 25 euro. It plugs into USB or a raspberry pi and the software is free (as in beer). I use SDR# from Airspy.
This is a couple of minutes traffic from a LoRa node building meetup.
The top graph is the current spectrum around 868 MHz, the lower graph is the history. The fuzzy red rectangles are spread spectrum LoRa transmissions.