Troubleshooting

Why rm on an open file frees nothing: a file is an inode, a name is only a link to it, and the blocks stay allocated until the link count is zero and every file descriptor is closed. Where df and du part ways, how to find the process holding the file, how to make it let go, and what the same problem looks like on a Kubernetes node.

nice and renice set a CPU scheduling weight and nothing else: the OOM killer reads oom_score, not NI. Why a lower nice cannot lift a cgroup cpu.max quota and why -10 versus +10 is a weight ratio of about 87 to 1 rather than 20 steps, what each field of top's %Cpu(s) line means and why it is every logical CPU summed, and why 717 tasks with 4 running means 713 of them are asleep.