Navigation bar disappears after system update on Galaxy Tab 2 7.0
Its very easy to bring back navigation bar on any android device. 


Download Root explorer or any other file explorer
access root permission and goto /system folder
Open build.prop and add this line    qemu.hw.mainkeys=0
If this line already there than it must contain 1 instead of 0. Change it to 0
Or use Gravity box to enable navigation bar.


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