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linux

  • A swap file on a small VPS, and the OOM killer it prevents

    Note1 min read

    A one-gigabyte VPS running MySQL, PHP and nginx has no headroom, and the kernel resolves that by killing the largest process — which is MySQL, mid-write. Swappiness at…

  • A logrotate config that does not lose the last hour

    Note2 min read

    Rotating a log by renaming the file leaves the writing process holding a handle to the renamed inode, so it keeps writing to a file nobody is looking…

  • Running as a non-root user in the image

    Note1 min read

    A container defaults to root, and root in the container is root on the host for anything mounted — so a build script that deletes a directory can…

  • The build cache misses on a file mode change

    Note1 min read

    A build that rebuilds from scratch on CI while being fully cached locally is usually not a Docker problem — it is that the checkout produced different file…

  • docker system prune, and the disk it gives back

    Note2 min read

    A development machine that builds images daily accumulates dangling layers, stopped containers and orphaned volumes, and none of it is visible until the disk fills. -a –volumes is…

  • journald rate limiting drops your logs silently

    Note1 min read

    systemd-journald discards messages from a service exceeding its burst limit and notes the fact in a single line that is easy to miss — so a debugging session…

  • Alerting that people do not learn to ignore

    Deep dive10 min read

    340 alerts in a month, four of which mattered. An alert channel nobody reads is the same as no alerting, and the cause is alerting on causes.

  • Logging drivers, and why json-file fills the disk

    Note1 min read

    The default driver writes every line to a JSON file with no rotation, so a chatty container quietly consumes the host disk and nothing points at it —…

  • Compose file version 3, and what swarm changed

    Deep dive10 min read

    v3 exists to be deployable to a scheduler, and that removes things a single-host file relied on. What went, why it had to, and what replaces it.

  • Centralised logging that answers a question

    Deep dive17 min read

    Four servers, eleven log files, and an incident reconstructed from three of them. Shipping first and parsing second, structured events, and the correlation id that makes it useful.