`tune2fs` - adjust tunable filesystem parameters on ext2/3/4

tune2fs [-l] [-m PERCENT] DEVICE

Options you will use

-l: List the superblock contents: block count, reserved blocks, mount options.
-m PERCENT: Set the reserved-blocks percentage (default 5, reserved for root).

Gotchas

That 5% reservation is why a normal user gets ENOSPC while root can still write. On a big data volume 5% of 40G is 2G wasted - tune2fs -m 1 is the usual fix.

Taught in

Try tune2fs in a real terminal Free, in your browser - a real Ubuntu terminal to try it in, with missions that check your work.