ADB can discover devices but not fastboot
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