When Chip is powered on, with GPIO0 pulled up, it enter into firmware downloading mode.
Download / install / git clone esptool.
Example usage:
./esptool.py --port /dev/ttyUSB1 --baud 9600 write_flash 0 ../nodemcu_float_0.9.6-dev_20150704.bin
Connecting... Erasing flash... Writing at 0x00001400... (1 %)
Erasing flash... Wrote 462848 bytes at 0x00000000 in 520.5 seconds (7.1 kbit/s)... Leaving...
./esptool.py --port /dev/ttyUSB1 --baud 9600 write_flash 0 ../nodemcu_float_0.9.6-dev_20150704.bin
./esptool.py --port /dev/ttyUSB1 --baud 115200 write_flash 0 ../nodemcu_float_0.9.6-dev_20150704.bin
nodemcu-master-14-modules-2016-06-27-15-50-54-float.bin