For those of you having trouble getting full root using CWM or TWRP root method on the GT-i9505, this is most likely caused by SetUID in the kernel.
To fix this issue, you can install any custom kernel after installing CWM or TWRP.
I do recommend installing Adam kernel by XDA user Wanam, as it’s stock-like yet should gives you better performance/battery life over stock.
Download Adam Kernel for GT-i9505 (You can install this using CWM or TWRP recovery)
Credits – Wanam <--- Please donate to the developer or hit "Thanks" on XDA!