配置环境 hadoop 环境真的是要命，随时都可以出现意向不到的问题，比如
Failing this attempt.Diagnostics: Call From hadoop001/0.0.0.0 to hadoop001:8020 failed on connection exception: java.net.ConnectException: 拒绝连接; For more details see: http://wiki.apache.org/hadoop/ConnectionRefused
很奇诡啊的问题，所有配置没问题，问题出现在 ipv6 上，
禁用掉系统的 ipv6 重启就好了
vi /etc/default/grub# cat /etc/default/grub
GRUB_TIMEOUT=5
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="ipv6.disable=1 crashkernel=auto rhgb quiet"
GRUB_DISABLE_RECOVERY="true"grub2-mkconfig -o /boot/grub2/grub.cfg reboot