Fastboot devices returns nothing I have Asus Fonepad 7  dual sim (Build ver. 5.5.1).  

I want to root my device. 

adb devices recognizes my device properly. 

Debugging
   mode is on.  

Even device enters in fastboot mode by executing adb reboot-bootloader in terminal (I am using Ubuntu 14.04).  

I have set
   up android rules in /etc/udev/rules.d/99-android.rules .  

I've
   found out my vendor id and product id using lsusb (when the device
   is in fastboot mode).  I've made corresponding entry in android rules
   file.  But even that didn't help.  

I've tried sudo fastboot devices
   also.  Every time I get nothing but a blank line.

Somebody please help!!
A bit of googling indicates that several people have had to build fastboot specifically to work with this device.  I found this one for Linux (last post) and have verified that it runs and isn't malicious: https://software.intel.com/en-us/forums/topic/494961