Docker pruner. Deletes docker's overlay2 leftovers that survive 'docker system prune -af --volumes'

docker-pruner.sh

#!/usr/bin/env bash

set -eEuo pipefail

MARKER_FILE_NAME="${DOCKER_PRUNER_MARKER:-DOCKER-PRUNER-MARKER-FILE}"
DOCKER_PATH="${DOCKER_PATH:-/var/lib/docker/overlay2}"

function _used_dirs() {
    for docker_obj in $(docker ps -aq) $(docker image ls -aq); do
        lowerdir="$(docker inspect "$docker_obj" | jq '.[].GraphDriver.Data.LowerDir' -r)"
        for dir in ${lowerdir//:/ }; do
            dirname "$dir"
        done
        dirname "$(docker inspect "$docker_obj" | jq '.[].GraphDriver.Data.MergedDir' -r)"
    done
}

function used_dirs() {
    _used_dirs | sort
}

function all_dirs() {
    find "$DOCKER_PATH"/ -maxdepth 1 -type d | grep -Ev '^'"$DOCKER_PATH"'/?l?$' | sort
}

function unused_dirs() {
    grep -v -xF -f <(used_dirs) <(all_dirs)
}

function set_marker() {
    touch "$1"/merged/"$MARKER_FILE_NAME" 2> /dev/null || \
        touch "$1"/diff/"$MARKER_FILE_NAME"
}

function _check() {
    for container in $(docker ps -aq); do
        docker exec "$container" ls "/$MARKER_FILE_NAME" && echo "container: $container" || true
    done
    for image in $(docker image ls -aq); do
        docker run --rm -it --entrypoint ls "$image" "/$MARKER_FILE_NAME" && echo "image: $image" || true
    done
}

function check() {
    output="$(_check 2>&1 | grep -Ev /"$MARKER_FILE_NAME'?"': No such file or directory')"
    if [[ -n "$output" ]]; then
        echo "Problem detected !"
        echo "$output"
        exit 1
    fi
}

function usage() {
    echo -e "Usage:
    \t$0 list    -- List all directories that needs to be removed
    \t$0 marker  -- Put a marker on each directory, to check if the marker in found in a running container (detecting an issue with $0)
    \t$0 check   -- Check if a marker is found. Must have run $0 marker first to make sense
    \t$0 clear   -- Remove the directories"
}

if [[ $# == 0 ]]; then
    usage ; exit 0
fi

if [ "$EUID" -ne 0 ]
  then echo "Please run as root"
  exit 1
fi


if [[ "$1" == "list" ]]; then
    unused_dirs
elif [[ "$1" == "marker" ]]; then
    export -f set_marker
    export MARKER_FILE_NAME="$MARKER_FILE_NAME"
    unused_dirs | xargs -I {} bash -c "set_marker {}"
elif [[ "$1" == "check" ]]; then
    check
elif [[ "$1" == "clear" ]]; then
    unused_dirs | xargs -I {} find {} -delete
    docker builder prune -af
elif [[ "$1" == "fn" ]]; then
    $2 "$@"
fi