no permissions (user in plugdev group; are your udev rules wrong?)

# run commends below on terminal
$ sudo apt-get install libmtp-common mtp-tools libmtp-dev libmtp-runtime libmtp9
$ sudo apt-get dist-upgrade

# remember the red text below
$lsusb
Bus 007 Device 002: ID 18d1:6jw2 Google Inc.
Bus 007 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 006 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 005 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 004: ID 8087:0aa7 Intel Corp.
Bus 001 Device 003: ID 04b4:2001 Cypress Semiconductor Corp.
Bus 001 Device 002: ID 045e:0823 Microsoft Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

# open the file and input the string below

$ sudo nano /etc/fuse.conf
SUBSYSTEM=="usb", ATTR{idVendor}=="18d1", ATTR{idProduct}=="6jw2", MODE="0666", GROUP="plugdev"

$ sudo udevadm control --reload-rules

$ adb devices

# Solved. right? :)