Ubuntu/Bespin/TIL

Main article: Ubuntu/Bespin

This page is the list of "today I learned" things that I learned while setting up a desktop Ubuntu 18.04 server.

Gnome

Gnome is highly configurable, but the GUI gives zero control over those settings.
Gnome themes are just files living in /usr/share/themes
More themes available online

Debian (Raspberry Pi, Kali) comes with dhcpcd baked in
Ubuntu comes with dhclient baked in
Difference between dhcpcd and dhclient? dhclient is older, provided by ISC, serves as a reference; dhcpcd is newer and more lightweight
Network manager is a surprisingly difficult service to stop
Ubuntu 18.04 server runs a stub dns server - resolv.conf, and the systemd-ressolved service - and it is extremely confusing because turning it off can disable the internet. So don't just go around deleting stuff!
In 18.04, ubuntu changed the way network interfaces are named, so the mac address is hard-coded in the device name
There is all kinds of shit in /etc/network/iface-up.d/ - it is a directory containing a bunch of scripts, each script is run once each time an interface is brought up. same thing with if-down and if-post-down and etc.
You can use any IP in the range 127.0.0.0/8 as a loopback IP address. Add up and down commands to the loopback entry in /etc/network/interfaces. See [1]
The IP addresses in /etc/resolv.conf that contain upstream nameservers have port 53 hard-coded, so there's no way to run multiple DNS servers on different ports. Instead, you can run different DNS servers on unusual loopback IP addresses, and access them that way.