CentOS7安装CDH5.12.0报错：could not contact scm server at localhost:7182

描述：DNS反向解析错误，不能正确解析Cloudera Manager Server主机名。如下日志：

Detecting Cloudera Manager Server...  
Detecting Cloudera Manager Server...  
BEGIN host -t PTR 192.168.1.198  
198.1.168.192.in-addr.arpa domain name pointer localhost.  
END (0)  
using localhost as scm server hostname  
BEGIN which python  
/usr/bin/python  
END (0)  
BEGIN python -c 'import socket; import sys; s = socket.socket(socket.AF_INET); s.settimeout(5.0); s.connect((sys.argv[1], int(sys.argv[2]))); s.close();' localhost 7182  
Traceback (most recent call last):  
File "", line 1, in   
File "", line 1, in connect  
socket.error: [Errno 111] Connection refused  
END (1)  
could not contact scm server at localhost:7182, giving up  
waiting for rollback request  

解决方案：将连不上的机器 /usr/bin/host 文件删掉,执行下面命令

mv /usr/bin/host /usr/bin/host.bak  

说明：不明白cloudera的初衷，这里已经得到 Cloudera Manager Server的ip了，却还要把ip解析成主机名来连接。由于DNS反向解析没有配置好，根据Cloudera Manager Server 的ip解析主机名却得到了localhost，造成之后的连接错误。这里的解决方案是直接把/usr/bin/host删掉，这样Cloudera Manager就会直接使用 ip进行连接，就没有错了。

参考：http://blog.itpub.net/31451369/viewspace-2153693/
https://student-lp.iteye.com/blog/2158979