Difficulty:: intermediate
Tools:: cron, docker

Problem

Docker keeps every layer it has ever pulled. On a build machine that is tens of gigabytes within a month, and the first symptom is a build failing on a full disk at an inconvenient hour.

Trigger

Cron, Sundays at 04:00.

Prerequisites

01Docker installed, and permission to talk to the daemon.
02A writable /var/log, or a different path in the line.
03Nothing on the machine that depends on an image it cannot pull again.

Steps

01
See what would go first docker
docker system df shows reclaimable space per category.
02
Add the line to root's crontab cron
sudo crontab -e. Talking to the docker socket needs root or membership of the docker group.
03
Check the log after the first Sunday
tail /var/log/docker-prune.log shows what was deleted and how much space came back.

Payload · cron

# Sunday 04:00. Removes images, containers, networks and build cache
# untouched for a week. Volumes are left alone on purpose.
0 4 * * 0 /usr/bin/docker system prune --all --force --filter "until=168h" >> /var/log/docker-prune.log 2>&1

Failure modes

!--all removes images with no running container, including one a stopped container needs at its next start. Drop --all to keep tagged images.
!An air gapped machine cannot re-pull what was pruned. Do not run this there.
!The until filter is relative to image creation, not last use. An old base image in daily use is still removed and pulled again.
!Volumes are untouched by design. Adding --volumes to this line deletes database data.

JSON-LD · HowTo

{
  "@context": "https://schema.org",
  "@type": "HowTo",
  "name": "Reclaim disk space from Docker every Sunday",
  "description": "A weekly cron line prunes Docker images, containers, networks and build cache untouched for seven days, and deliberately leaves volumes alone so data survives.",
  "url": "https://automationsanonymous.com/automations/reclaim-disk-space-from-docker-weekly",
  "tool": [
    {
      "@type": "HowToTool",
      "name": "cron",
      "url": "https://automationsanonymous.com/tools/cron"
    },
    {
      "@type": "HowToTool",
      "name": "docker",
      "url": "https://automationsanonymous.com/tools/docker"
    }
  ],
  "step": [
    {
      "@type": "HowToStep",
      "position": 1,
      "name": "See what would go first",
      "text": "docker system df shows reclaimable space per category.",
      "url": "https://automationsanonymous.com/tools/docker"
    },
    {
      "@type": "HowToStep",
      "position": 2,
      "name": "Add the line to root's crontab",
      "text": "sudo crontab -e. Talking to the docker socket needs root or membership of the docker group.",
      "url": "https://automationsanonymous.com/tools/cron"
    },
    {
      "@type": "HowToStep",
      "position": 3,
      "name": "Check the log after the first Sunday",
      "text": "tail /var/log/docker-prune.log shows what was deleted and how much space came back."
    }
  ],
  "datePublished": "2026-09-05T16:53:32.236Z"
}