dockerfile创建ubuntu，postfix配置选择时停止

 开发四年只会写业务代码，分布式高并发都不会还做程序员？->>>    dockerfile创建ubuntu16.04,官网源 ubuntu安装完成，执行dockerfile后续命令。 到这一步， RUN apt-get install -y dovecot-imapd dovecot-pop3d postfix 终端dovecot安装完，postfix安装时出现选择项： Selecting previously unselected package postfix. Preparing to unpack .../postfix_3.1.0-3_amd64.deb ... debconf: unable to initialize frontend: Dialog debconf: (TERM is not set, so the dialog frontend is not usable.) debconf: falling back to frontend: Readline Postfix Configuration --------------------- Please select the mail server configuration type that best meets your needs. No configuration: Should be chosen to leave the current configuration unchanged. Internet site: Mail is sent and received directly using SMTP. Internet with smarthost: Mail is received directly using SMTP or by running a utility such as fetchmail. Outgoing mail is sent using a smarthost. Satellite system: All mail is sent to another machine, called a 'smarthost', for delivery. Local only: The only delivered mail is the mail for local users. There is no network. 1. No configuration 3. Internet with smarthost 5. Local only 2. Internet Site 4. Satellite system General type of mail configuration: 上面我选了2，然后就没有任何动静了。。。。。 网上有说用apt-get install -y -o Options::="2" postfix 实验无果. 怎样才能自动安装选择呢？