Apple don’t have a FastBoot option in iOS devices like in Android phones. But
for all jailbroken users who didn’t know, FastBoot is a cydia tweak which lets you
sleek menu to pop up with three options( Respring, SafeMode and Reboot) while
holding your power button. Though there are many alternative tweaks avaialable
in Cydia but FastBoot allows you to customize pop up appeareance with DarkMode,
Shadows and rounded corners.
tweak, just go to cydia and search for FastBoot and install it. If you are not
yet jailbroken then follow this guide on How to jailbreak iOS 9.0.2 using Pangu? and jailbreak your device immediately and
customize your device with lot more tweaks, themes and more. After installing
this tweak, you will get a preferences options in the settings app. It’s very easy and efficient way to boot your device while you are in homescreen or using any other applications.