Disk full, but the du command finds nothing
df says 90%, du adds up to 14 KB: a 150 MB log removed with rm, still held open by a process. lsof +L1, /proc/PID/fd, truncating through : > /proc/PID/fd/N, the sparse file without O_APPEND, logrotate copytruncate versus create with a signal, and the container case, measured on a 200 MB ext4.