问题
安装cloudera namager时，cloudera-scm-server可以正常启动，cloudera-scm-agent启动失败。 
 
查看日志 
/opt/cm-5.7.0/log/cloudera-scm-agent/cloudera-scm-agent.out的内容，打印一下内容：

/opt/cm-5.7.0/lib64/cmf/agent/build/env/lib/python2.6/site-packages/cmf-5.7.0-py2.6.egg/cmf/parcel.py:17: DeprecationWarning: the sets module is deprecated
  from sets import Set
[11/May/2016 10:12:05 +0000] 31760 MainThread agent        INFO     SCM Agent Version: 5.7.0
Unable to create the pidfile.

解决
执行命令
mkdir /opt/cm-5.7.0/run/cloudera-scm-agent
再次尝试，启动成功。