Oct. 30, 2022, 9:51 p.m. -  Ihar

Problem: Cannot open /dev/ttyUSB0: Permission denied error is caused by the user not having access to the serial ports as other commenters have mentioned. More specifically, the user is not in the dialout group. Solution: sudo usermod -a -G dialout $USER From: https://github.com/esp8266/source-code-examples/issues/26#issuecomment-631138497