docker-compose的疑问

Question

1，最近看了一下docker-compose的一些知识，有个疑问要请教。

为啥这里定义的环境变量是这些呢？

我如何知道这些镜像需要哪些环境变量呢？谢谢

相关代码

//

version: "3"
services:
  php:
    image: php:7.2.3-fpm
    networks:
      - lnmp
    volumes:
       -  ./web:/web
    environment: 
      - TZ=Asia/Shanghai
  nginx:
    image: nginx:1.13
    networks:
      - lnmp
    ports:
      - 80:80
    volumes:
      - ./web:/web
      - ./nginx/nginx.conf:/etc/nginx/nginx.conf
      - ./nginx/conf.d/default.conf:/etc/nginx/conf.d/default.conf
    environment: 
      - TZ=Asia/Shanghai
    links:
      - php
  mysql:
    hostname: mysql
    image: mysql:5.6
    environment:
     - TZ=Asia/Shanghai
    ports:
      - 3306:3306
    networks:
      - lnmp
    volumes:
      - ./mysql/conf:/etc/mysql/conf.d
      - ./mysql/data:/var/lib/mysql
    environment:
     MYSQL_ROOT_PASSWORD: 123456
networks:
  lnmp:

为啥需要这些变量呢？谢谢
TZ=Asia/Shanghai
MYSQL_ROOT_PASSWORD: 123456

Answer 1

去查看mysql:5.6的Dockerfile就可以了

Answer 2

dockerhub上找对应镜像的dockerfile文件里ENV关键字
或者
进入容器，敲export