Thanks, it worked. Probably a bad connection.

Hello, I tried both methods to flash the legacy, but after a while it stops and I get this :

2017/06/03 21:50:47 Done pushing /home/frederic/.cache/ubuntuimages/pool/keyring-4c4e7ef380ebcfa2c31084efa199138e93bfed8fc58aa3eb06bdf75a78af9b57.tar.xz to device
18.24 MB / 69.21 MB [=======>_________________________] 26.35 % 32.19 KB/s 27m1s
2017/06/03 22:00:11 unexpected EOF

Move to your device to finish the setup.

Cleaning up..

Exiting script. Bye Bye

Any suggestions?
Thanks !