I have a four node cluster running on Centos 6.5, which are all VMs so adjusting memoery is simple.  One node has 20 gb RAM, and the other 4 have 4 gb RAM.  I installed everything using the Cloudera Manager and am now getting a configuration warning of "Memory on host xxx.xxx.xxx.xxx is overcommitted. The total memory allocation is 18.3 GiB bytes but there are only 19.5 GiB bytes of RAM (3.9 GiB bytes of which are reserved for the system). Visit the Resources tab on the Host page for allocation details. Reconfigure the roles on the host to lower the overall memory allocation. Note: Java maximum heap sizes are multiplied by 1.3 to approximate JVM overhead."

On my first attempt of building a cluster I got all the web interfaces working but when I restarted my servers to adjust the amount of memory it seemed as though everything stopped working and I couldnt get the web page to laod aagain or see the services.

Ive read through the proper order of stopping services in cloudera manager but how do you restart the namenode and datanode servers as to not stop any functionality?