Install both ESP32 and ESP8266 on Arduino IDE, run on Ubuntu.

Before install ESP32/8266 on Arduino IDE running on Ubuntu, python is needed to be installed. Otherwise, you will be reported with error of:
exec: "python": executable file not found in $PATH

To install python and wget on Ubuntu, run the command in terminal:
$ sudo apt install python
$ sudo apt install python-pip
$ pip install wget

The simplest way to install ESP32/8266 on Arduino IDE is using Boards Manager,

To add boards manager, click in the menu
> File > Preferences >

Enter https://dl.espressif.com/dl/package_esp32_index.json (for ESP32) or/and http://arduino.esp8266.com/stable/package_esp8266com_index.json (for ESP8266) in Additional Boards Manager URLs. When add multiple URLs, separating them with commas.

This video show how:


If you run with error of:
ImportError: No module named serial.tools.list_ports

Most likely the pyserial is too old, re-install it with:
$ pip install pyserial

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Updated@2020-06-26:
If you are looking for Ubuntu 20.04, read it Install ESP32/ESP8266 to Arduino IDE on Ubuntu 20.04, with setup Pythton & serial.