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

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: systemctl enable syncthing@username.service
Start the service: systemctl start syncthing@username.service
Check the status: systemctl status syncthing@username.service

The magic sequence to wake up Apple's SuperDrive on Linux

sudo apt-get install sg3-utils (only needed the first time)
ls /dev (to check whether sr0 or sr1, usually it's sr0 unless you had already other USB drives connected)
sg_raw /dev/sr0 EA 00 00 00 00 00 01

Deleting files with "illegal characters"

In the cross-platform environment of our university, at least three different OS connect to the smb shared group directories. Apparently Macs are able to save files with characters that are not allowed on other platforms and which cannot be easily deleted. Recently we had several files which ended with a '.' (dot) or a ' ' (space), and we were not able to remove them via the GUI. In Windows 7, I managed via the command line with:
delete "file." or
delete "file "

Windows changes my computers clock

If I am not mistaken, Windows is the only OS, that uses local time for the system clock (instead of UTC). This means that in multiple boot configurations, every restart of the system into Windows will screw up the system time. In order to reset it (in Ubuntu 16.04), use
sudo timedatectl set-timezone Etc/UTC


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