I was running a little home‑lab server on a 2 GB SSD. The board was an Orange Pi Zero‑like single‑board computer, and it was juggling a personal web server, a GitLab instance, and a handful of containerised apps. After a month of steady traffic, the SSD hit 100 % on /var. The culprit? systemd‑journald had quietly gobbled up the whole drive.
journald is the default logger on most modern distros. It keeps logs in binary form under /var/log/journal. By default it will keep everything until the filesystem is full, then start deleting the oldest entries. On a tiny SSD that can happen faster than you can say “disk full”.