first commit

.dockerignore

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+!entrypoint.sh

Dockerfile

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+ARG ALPINE_VERSION=3.21
+FROM alpine:${ALPINE_VERSION}
+
+ARG SUPERCRONIC_VERSION=0.2.33
+# TARGETARCH is auto-set by buildx per platform: "amd64", "arm64", etc.
+ARG TARGETARCH
+
+RUN apk add --no-cache docker-cli
+
+ADD https://github.com/aptible/supercronic/releases/download/v${SUPERCRONIC_VERSION}/supercronic-linux-${TARGETARCH} \
+    /usr/local/bin/supercronic
+RUN chmod +x /usr/local/bin/supercronic
+
+# Match GID to your host's docker group. Check with: stat -c '%g' /var/run/docker.sock
+ARG DOCKER_GID=999
+RUN getent group ${DOCKER_GID} || addgroup -g ${DOCKER_GID} dockersock && \
+    adduser -D -G $(getent group ${DOCKER_GID} | cut -d: -f1) cannibal
+
+COPY entrypoint.sh /entrypoint.sh
+RUN chmod +x /entrypoint.sh
+
+USER cannibal
+
+ENTRYPOINT ["/entrypoint.sh"]

README.md

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+# Cannibal
+
+eats docker data omnom nom
+
+## But what it really does?
+
+Runs docker system prune periodically

build.sh

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+#!/bin/sh
+set -e
+
+IMAGE="${IMAGE:-docker-pruner}"
+TAG="${TAG:-latest}"
+DOCKER_GID="${DOCKER_GID:-$(stat -c '%g' /var/run/docker.sock)}"
+SUPERCRONIC_VERSION="${SUPERCRONIC_VERSION:-0.2.33}"
+ALPINE_VERSION="${ALPINE_VERSION:-3.21}"
+
+if ! docker buildx inspect multibuilder > /dev/null 2>&1; then
+    echo "Creating multibuilder..."
+    docker buildx create --name multibuilder --use
+else
+    docker buildx use multibuilder
+fi
+
+echo "Building ${IMAGE}:${TAG} for linux/amd64 and linux/arm64"
+echo "  Alpine:      ${ALPINE_VERSION}"
+echo "  Supercronic: ${SUPERCRONIC_VERSION}"
+echo "  DOCKER_GID:  ${DOCKER_GID}"
+
+docker buildx build \
+    --platform linux/amd64,linux/arm64 \
+    --build-arg ALPINE_VERSION="${ALPINE_VERSION}" \
+    --build-arg SUPERCRONIC_VERSION="${SUPERCRONIC_VERSION}" \
+    --build-arg DOCKER_GID="${DOCKER_GID}" \
+    --tag "${IMAGE}:${TAG}" \
+    .

docker-compose.yml

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+services:
+  cannibal:
+    image: cannibal:latest
+    build:
+      context: .
+      args:
+        DOCKER_GID: "${DOCKER_GID:-999}"
+    restart: unless-stopped
+    environment:
+      PRUNE_SCHEDULE: "0 3 * * *"  # every day at 3am
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+    group_add:
+      - "${DOCKER_GID:-999}"

entrypoint.sh

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+#!/bin/sh
+set -e
+
+echo "Docker pruner starting as $(whoami). Schedule: ${PRUNE_SCHEDULE}"
+
+# Write crontab from env var at runtime
+CRONTAB_FILE=/tmp/crontab
+echo "${PRUNE_SCHEDULE} docker system prune -af >> /tmp/prune.log 2>&1" > "${CRONTAB_FILE}"
+
+exec supercronic "${CRONTAB_FILE}"