update firmware in linux on Expansion Board v3

[Prx]

hi,
I try to update the V3 Exp Board on Linux .
I installed dfu-util
I made the following :

• Disconnect the USB cable
• Hold down the S1 button on the shield
• Connect the USB cable
• Keep the S1 button pressed for at least one second
• Release the button. When the board is connected in DFU-mode, it will be in this state for 7 seconds.

If you enter for list:
$> dfu-util -l
you get :
Found Runtime: [04d8:ef99] devnum=0, cfg=1, intf=0, alt=0, name="UNDEFINED"

So I enter the command:
$>dfu-util -D ./expansion3_0.0.9.dfu
and I get as answer :
"Cannot open device
Opening DFU USB device... "
and nothing else but the prompt: $

Do I make it correct ? How do I know that it is correct or not?
Is there a mistake ?
thanks

[Prx]

@tealbrains & @Xykon : thanks all , that was that ! sudo dfu-util -D ./expansion3_0.0.9.dfu -R -v (I had added my user to dialout group already : not enought)

[Xykon]

@prx Did you give r+w access to the serial devices for the current user?

On most Linux systems this is done using sudo usermod -a -G dialout $USER (you'll need to logout and/or reboot for the change to become effective).

[tealbrains]

@prx try sudo