Limits, OOMKilled and the user in a container

Articles

• Exit codes: $?, && and || — An exit code is a number from 0 to 255 that a command reports: 0 means success, anything else a failure or a "no".
• Docker — containers: running, ports, volumes, networks — A container platform: the dockerd service creates and runs containers from images, the docker command drives it. Access to the service is for root and the docker group.
• Users and groups — Linux accounts and groups; usermod -G without -a replaces all of a user's supplementary groups instead of adding one.
• Memory and swap: free, available and the page cache — How to read free: used and free memory, the page cache and available; swap, a swap file and vm.swappiness.
• cgroups and namespaces — how containers work — Isolation (namespaces) and resource limits (cgroups) — the foundation of containers and systemd.