Dear Y'all
I am using ubuntu 16.04 lts and I just sudo apt-get install'ed arduino.
I am trying to install the esp8266 cores but I cannot enter extra board URLs in preferences. The entry simply isn't there and I also cannot find the board manager. It certainly is not where it usully is.
The version of the arduino IDE seems to be 2:1.0.5+dfsg2-4
How can I get my cores? I desperately need to program a wemos d1 mini so I can finally have light in me livingroom 
Tnx in advance.
When you install the Arduino IDE via apt-get install arduino you get a super outdated and non-standard version of the IDE, this 2:1.0.5+dfsg2-4. That's why you are missing many modern features.
You should always install the official Arduino IDE downloaded from:
yeah I figured something like that. I already downloaded a .deb from the web. And it works much better.
I could upload a program to a d1 mini, only not the one I wanted. The one I wanted to program is already soldered on a PCB. And I only used 4 I/O pins of which none of them is the Tx or Rx, but this is a problem for another topic.
bask185:
I already downloaded a .deb from the web. And it works much better.
I wouldn't trust that either. The people putting these things together often don't fully understand how Arduino works and then we spend a lot of time trying to help people solve problems that would never have happened with the official IDE. It's really a shame that the Arduino team don't take control of the package manager situation instead of leaving it in the hands of random 3rd parties.