jeltsch's blog

Scanning my home network (nmap)

Scanning my home network for all devices that are listening
on port 80 (http):
nmap -p80 -oG - | grep 80/open
Sometimes this doesn't work (because nmap tries to be smart and only scan hosts that are available). In order to make nmap scanning without intelligence, use the e-Pn (no ping) option. This scans all ports of host
nmap -Pn -p0-65535

Computer time: Windows against the rest of the world

I am not sure, but Windows seems to be the only operating system, that wants the computer clock to be set to the local time zone instead of universal standard time (UTC). Maybe that is a relic of the times when Microsoft thought that the internet was not very important for the future of computing. All other operating systems apparently use UTC: MacOS, Android, Linux, BSD, ... However, if you are dual-booting your computer, you can get into trouble. Not all operating systems detect automatically a dual boot install and adjust their behaviour in order to be compatible with Windows.


Syncthing is one of the best tools for keeping folders synchronized across the internet. However, for one or the other reason, it occasionally stops to work on my Ubuntu 16.04 and because I use it in a "set it and forget it" fashion, I also forget how to check that it is operational.
Make it start automatically at boot time (as a system service): systemctl enable syncthing@username.service
Start the service: systemctl start syncthing@username.service