My company has blocked the Arduino library downloads (like many others, nothing personal...). I was able to separately download the bz2 file that the IDE was trying to download, the file name is:
avr-gcc-7.3.0-atmel3.6.1-arduino7-arm-linux-gnueabihf.tar.bz2
How do I install it manually under IDE 2.0?
Thanks in advance!
You should note that this is not a library. This is part of the toolchain of a boards platform.
The process is exactly the same for Arduino IDE 2.0 as for the classic Arduino IDE. The boards platforms and tools are stored in the same place with the same folder structure.
The best approach is to do the installation on a computer with free access to the Internet, then copy the complete installation from that computer to the one without Internet access. On Linux, this is the ~/.arduino15 folder. Just copy that whole thing from one computer to the other and you'll be good. Make sure that both computers are of the same host architecture because the installed tools are chosen according to the the architecture of the computer they are installed on.
Thank you, I am not sure I can do that because the machine is pretty well locked down but I can certainly try 
I am on Windows 10 64 bits.
I assume that by "the complete installation", you mean the "Arduino IDE" folder under Program Files
I have another Windows 10 64 bit machine with the tools installed and working, so I will copy that entire folder from one machine to the other.
didier9:
I assume that by "the complete installation", you mean the "Arduino IDE" folder under Program Files
No. By "the complete installation", I mean the entire boards package: platform and toolchain. That is completely separate from the Arduino IDE 2.0 installation.
On Windows, it's located at:
C:\Users<user name>\AppData\Local\Arduino15
If you copy the contents of that folder from one Windows machine to the other then all your boards you installed via Boards Manager (Tools > Board > Boards Manager or click the chip icon on the left side bar) in the Arduino IDE will be transferred.