I'm creating an advertisement display, based on RaspberryPi (no real time clock present) and piCore, which is busybox-based tinycorelinux. It will be behind a firewall, and even within its own network segment it should never make an outgoing connection, but only receive stuff, like a picture to display (via VNC listening client) or current datetime. It is not known in advance, what host(s) will send stuff; luckily, everything from own segment is okay to accept.
So polling pool.ntp.org is obviously not an option. According to ntpd(8), "ntpd can operate in any of several modes, including symmetric active/passive".
- Is it possible to start ntpd in way that it sends no requests but accepts (S)NTP packets?
- If not ntpd, anything else? (possibly from RaspberryPi / busybox repertoire)
- Hosts sending stuff to my RaspberryPi are Windows10 PCs. I cannot install programms there, but only run portable stuff. My plan is to write a script to write the (S)NTP packet content into a file and then send it with packetsender. Any simpler ways?