ADB can discover devices but not fastboot I've searched on the web about this problem and it's usually solved by installing the appropriate drivers. Problem is I'm on a Mac.

When I plug in my device, it can be discovered when I run adb devices. I run adb reload bootloader and it goes into download mode (the mode you get when you hold Volume Down + Home button when powering up). Is this correct? I assume it is.

Anyway, when it is in this stage, adb devices or fastboot devices yields nothing.

I have tested this on i9100 and i9505.
To make the system recognize the Android device, in their several modes, one needs to set permissions for his user in udev.

You need to repeat this process of loading Android udev IDs, for every mode the phone has (operating system, bootloader or recovery) because they have different USB IDs

# reboot into fastboot mode
adb reboot bootloader

# grab you fastboot/bootloader device ids
lsusb
&gt; Bus 001 Device 035: ID **18d1:d00d** Google Inc.

# install the ids into /etc/udev/rules.d/99-android.rules
SUBSYSTEM=="usb", ATTR{idVendor}=="18d1", ATTR{idProduct}=="d00d", MODE="0666", OWNER="thiago"

# restart udev
/etc/init.d/udev restart

# try fastboot (only on bootloader mode)
fastboot devices