CUPS无法打印，报错“Unable to encrypt connection”

问题现象
CUPS使用http连接打印机无法打印，Samba共享连接打印正常
访问CUPS管理页面响应慢，无法访问https管理页面，CUPS错误日志内容如下

[Client 55] Unable to encrypt connection: A TLS fatal alert has been received.
[Client 56] Unable to encrypt connection: The TLS connection was non-properly terminated.

解决方法
禁用CUPS的https功能
在配置文件cupsd.conf中加一行DefaultEncryption Never
重启CUPS服务

来源：https://serverfault.com/questions/311799/centos-cups-configuration