You should be able to see inode usage with `df -i`, no? I usually use `df -Tih` (print the file system type, list inode usage, in human-readable format).

I've had the other case where `df` says the disk is full with plenty of inodes left, but then `ncdu` says there is plenty of space (supposedly).

Lo' and behold, you have some borked process still holding GBs of log files open that you thought you "deleted" -- really unlinked from a directory.

tl;dr: Don't forget `lsof +L1` to find pesky processes that are holding files open that you unlinked from a directory but have yet to be actually marked as deleted on the filesystem [1]. The space on disk won't be freed until the process closes the files or is terminated. (Technically, the open files are associated with a mount point, not the file system itself, which makes dealing with symbolic links across file systems somewhat confusing.)

[1]: For example, see https://unix.stackexchange.com/a/141639/332116)