Since I'm running my entire OS from a damned jump drive, I need every scrap of space I can find. I can't afford a 5% system reserve in my /home partition. For me, that's 1 GB out 20. I wanna 'ave it BACK! (Said the temper tantruming warfacegod. Gimme it. 'T's Mine! My Precious!) Right! Moving along.. eehheemmm!
sudo tune2fs -m 0 /dev/sdb3
tune2fs 1.42.12 (29-Aug-2014) tune2fs: Filesystem has unsupported read-only feature(s) while trying to open /dev/sdb3 Couldn't find valid filesystem superblock.
I've already tried using a higher percentage. Same result. Also, setting the reserve to 0% on sdb2 (my root partition) worked just fine. (Normally wouldn't do that but I needed to test tunefs.)