docker의 nextcloud - 데이터베이스 초기화 중 오류가 발생했습니다.

nextcloud 컨테이너를 시작할 때 docker-compose up다음 오류가 발생했습니다.

db_1_7bb6e5f5b725 | Initializing database
db_1_7bb6e5f5b725 | mkdir: cannot create directory '/var/lib/mysql//mysql': Permission denied
db_1_7bb6e5f5b725 | Fatal error Can't create database directory '/var/lib/mysql//mysql'
db_1_7bb6e5f5b725 | 
db_1_7bb6e5f5b725 | The latest information about mysql_install_db is available at
db_1_7bb6e5f5b725 | https://mariadb.com/kb/en/installing-system-tables-mysql_install_db
test_db_1_7bb6e5f5b725 exited with code 1

지정된 docker-compose는 다음과 같습니다.

version: '2'

volumes:
  nextcloud:
  db:

services:
  db:
    image: mariadb
    user: www-data
    command: --transaction-isolation=READ-COMMITTED --binlog-format=ROW
    restart: always
    volumes:
      - db:/var/lib/mysql
    environment:
      - MYSQL_ROOT_PASSWORD=***
      - MYSQL_PASSWORD=***
      - MYSQL_DATABASE=nextcloud
      - MYSQL_USER=nextcloud

  app:
    image: nextcloud
    ports:
      - 8080:80
    links:
      - db
    volumes:
      - nextcloud:/var/www/html
    restart: always