Manual garbage collector for gitlab registry, it removes old revisions that are not referenced by any tag

gitlab-gc.sh

#!/bin/bash

BASE_PATH=/var/opt/gitlab/gitlab-rails/shared/registry/docker/registry/v2/repositories

DRY_RUN=0
KEEP_LAST_IMAGES=10
RUN_GARBAGE_COLLECTOR=0
GITLAB_CTL_COMMAND=`which gitlab-ctl`


if [ ! -x "${GITLAB_CTL_COMMAND}" ]; then
    echo "Missing gitlab-ctl command"
    exit 1
fi


while (( "$#" )); do
    case "$1" in

        "-b" | "--base-path")
            BASE_PATH=$2
            shift
            ;;

        "-r" | "--run-gc")
            RUN_GARBAGE_COLLECTOR=1
            ;;

        "-d"|"--dry-run")
            DRY_RUN=1
            ;;

        "-k"|"--keep")
            if ! ( echo $2 | grep -q '^[0-9]\+$') || [ $2 -eq 0 ]; then
                echo "Invalid value for keep last images '$2'"
                exit 1
            fi
            KEEP_LAST_IMAGES=$2
            shift
            ;;

        "-h"|"--help")
            echo "Usage: ${0} [options]"
            echo "Options:"
            echo -e "\t-k NUM, --keep NUM"
            echo -e "\t\tKeeps last NUM revisions, except current tags"
            echo
            echo -e "\t-d, --dry-run"
            echo -e "\t\tEnables dry run, no changes will be made"
            echo
            echo -e "\t-b, --base-path"
            echo -e "\t\tSets base path of Gitlab Registry repository storage"
            echo
            echo -e "\t-r, --run-gc"
            echo -e "\t\tStarts garbage collector after revision removal"
            exit 0
            ;;

        *)
            echo "Unknown argument: $1"
            exit 1
            ;;
    esac
    shift
done

IFS=$'\n'
used_hashes=`mktemp`
marked_hashes=`mktemp`
for repository in `find ${BASE_PATH} -mindepth 2 -maxdepth 2 -type d | sed "s#${BASE_PATH}/##"`; do
    for tag_hash in ${BASE_PATH}/${repository}/_manifests/tags/*/current/link; do 
        cat "${tag_hash}" | cut -d':' -f2; 
    done > "${used_hashes}"
    
    echo "Removing revisions of $repository:"
    ls -t ${BASE_PATH}/${repository}/_manifests/revisions/sha256 | fgrep -vf "${used_hashes}" | tail -n+${KEEP_LAST_IMAGES} | tee ${marked_hashes}
    if [ ${DRY_RUN} -ne 1 ]; then
        cat ${marked_hashes} | sed "s#^#${BASE_PATH}/${repository}/_manifests/revisions/sha256/#" | xargs rm -rf 
    fi
done
rm ${used_hashes}
rm ${marked_hashes}


if [ ${DRY_RUN} -eq 0 -a ${RUN_GARBAGE_COLLECTOR} -eq 1 ]; then
    "${GITLAB_CTL_COMMAND}" registry-garbage-collect
fi

This is my revision if you want to take a look:
https://gist.github.com/eedugon/69da0397c142e56f4186ee691502e7ee

Small features added:

• Searching in all BASE_PATH, not fixing the search to a depth of 2
• Directories without valid tags or revisions directories won't be processed (to avoid unexpected issues)
• Logging in case there's nothing to delete
• running registry-garbage-collect only if something was deleted
• Added crontab example