Why can't I upload a sketch to the Arduino Leonardo?

Question

linux

This is my mistake

Caused by: jssc.SerialPortException: Port name - /dev/ttyACM0; Method name - openPort(); Exception type - Permission denied.
  at jssc.SerialPort.openPort(SerialPort.java:170)
  at processing.app.Serial.touchForCDCReset(Serial.java:81)
  ... 7 more

System: Ubuntu 20.04 LTS

Answer 1

the user does not have access to the /dev/ttyACM0 device,
look at the rights to this device
ls -la /dev/ttyACM0
and add the user to the appropriate group.
I don’t have Ubuntu at hand, but it could be something like usb

Answer 2

When the development environment starts uploading the binary file to the controller ("Download" mode),
try pressing the "Reset" button on the Arduino Leonardo board.
If I'm not mistaken, this will launch the "Loader" which will organize access to the controller's memory.