Getting error while flashing on ESP32-devkit

[Vrutha]

Serial port /dev/ttyUSB0
Connecting........_____....._____....._____....._____....._____....._____....._____

A fatal error occurred: Failed to connect to ESP32: Invalid head of packet (0x35)
CMake Error at run_cmd.cmake:14 (message):
  esptool.py failed
Call Stack (most recent call first):
  run_esptool.cmake:21 (include)


FAILED: CMakeFiles/flash
cd /home/vrutha/esp/esp-idf/components/esptool_py && /usr/bin/cmake -D IDF_PATH="/home/vrutha/esp/esp-idf" -D ESPTOOLPY="/home/vrutha/.espressif/python_env/idf4.2_py2.7_env/bin/python /home/vrutha/esp/esp-idf/components/esptool_py/esptool/esptool.py --chip esp32" -D

[OutOfLine]

while you see the "_____.....___" building up press one of the buttons for some seconds
labelling of the buttons may vary, just try