Can't re-lock bootloader

[Dubbayoo]

So I've got this 2012 Nexus 7, see? I'm rooted and I've got TWRP installed. I haven't really needed to mess with it in so long I've forgotten why I even have TWRP. I don't really mess with ROMs. I just like having root for apps that need it.

Anyway, I still haven't installed the KitKat update because I can't lock the bootloader. I tried running "fastboot-linux oem lock" (I have both Linux and OSX at home) and if I recall it just hangs there. Can someone please get me back on track to lock the bootloader so I can install kit kat? TIA.