How to root the SM-G900F Android 5.0 without tripping KNOX?
I did it following from this guide here. Broadly (though I strongly suggest you follow the guide):

1) make backups

2) buy mobile Odin Pro from android market (5 USD)

3) downgrade using Odin (normal one on PC) to 4.4.

4) install towelroot and run it

5) use mobile Odin to flash rooted lollipop ROM *

6) use normal odin to flash compatible bootloader and modem.

*For some reason, using mobile Odin did not trip Knox when I did this, per the guide I linked. It still warned me that Knox would be tripped, even though it wasn't. I have no idea why it didn't trip Knox, so I can't guarantee it won't when you do it.