adb devices ???????????? no permission

Solution:

在/etc/udev/rules.d/目录下创建51-android.rules文件，

sudo vi /etc/udev/rules.d/51-android.rules

只要在51-android.rules中保留一行

SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", MODE="0666"

就好了~
修改以后重新插入你的Android设备，运行adb devices命令看看：

yajun@yajun-ThinkPad-X220:~/Downloads$ adb devices
List of devices attached 
???????????? no permissions


yajun@yajun-ThinkPad-X220:~/Downloads$ adb devices
List of devices attached 
MT-HYOFKZ6SYHUCK77P device