cfm880@cfm880:~$ adb devices
List of devices attached
93CY18K0U	no permissions (missing udev rules? user is in the plugdev group); see [http://developer.android.com/tools/device.html]

cfm880@cfm880:~$ lsusb
Bus 002 Device 002: ID 18d1:4ee7 Google Inc. Nexus/Pixel Device (charging + debug)
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 004: ID 0e0f:0008 VMware, Inc. Virtual Bluetooth Adapter
Bus 001 Device 003: ID 0e0f:0002 VMware, Inc. Virtual USB Hub
Bus 001 Device 002: ID 0e0f:0003 VMware, Inc. Virtual Mouse

$ sudo vim /etc/udev/rules.d/90-android.rules
SUBSYSTEM=="usb",ATTRS{idVendor}=="18d1",MODE="0666",GROUP="plugdev"

cfm880@cfm880:~$ sudo udevadm control --reload-rules
cfm880@cfm880:~$ sudo service udev restart
cfm880@cfm880:~$ sudo udevadm trigger
cfm880@cfm880:~$ adb kill-server
cfm880@cfm880:~$ adb start-server
* daemon not running; starting now at tcp:5037
* daemon started successfully
cfm880@cfm880:~$ adb devices
List of devices attached
93CY18K0U	device