My ROS2 Docker Container Disappeared After a Month—What Happened?

If Docker’s image and container lists look empty, check whether Docker’s data directory is on an external drive that failed to mount. On a Raspberry Pi, this is a common cause. Useful commands include `lsblk -f`, `blkid`, `df -h -T`, `findmnt`, and `cat /etc/fstab`. You can also inspect `/var/lib/docker/containers/`; directories with long hexadecimal names indicate that the container data may still exist but Docker is currently using a different data root.

First check whether the images and stopped containers still exist with `docker images` and `docker ps -a`. If the images are present but the container is missing, the most likely explanations are that it was started with `--rm`, which automatically deletes it when it stops, or that a cleanup command such as `docker system prune` removed it. A reboot during that time could also have triggered the issue if `--rm` was used. Docker Compose is a good way to keep the container definition in a permanent file so recreating it is easy.

Docker doesn’t keep an unlimited history of past events—`docker events` mainly reports activity while it is running—so not seeing a removal event doesn’t prove the container was never deleted. If the Docker directory is actually empty, other possibilities include an automated `docker system prune`, the container having been launched with `--rm`, or filesystem problems on the Pi’s SD card. Check for storage errors with `dmesg -T | grep -iE "ext4|i/o error"` and inspect `lost+found`. For the future, store the setup in a Compose file alongside the project so the container can be recreated easily.