Phone isn't rooted after installing SuperSU I'm trying to root HTC Desire 500 Dual Sim. I've been following along this video tutorial:
https://www.youtube.com/watch?v=yWLK5XhsVAE

I've unlocked the bootloader and installed CWM Recovery without any issues. When I go into recovery, select "Install zip" and install SuperSU zip, the installation process finishes just fine, it doesn't show any errors, but after I reboot there are no new apps installed and I don't have root access (tested with Root Checker app).

I've tried multiple version of SuperSU (0.96, 0.98, 2.79, etc.), but none of them worked.
Also, I can't mount /system while in CWM, not sure what it means.

What could possible cause this? Is there anything I can do?
It seems like HTC Desire 500 has a "system write protection", so you may need to flash a custom (modified) kernel to prevent the system from protecting itself from modification.  

Check this post on XDA forum.