A simple example

 <xml>
       <master>master1</master>
       <name>all</name>
       <override>all</override>
       <group>
               <name>Login</name>
               <image>RHEL5</image>
               <override>Login</override>
               <node>node001</node>
               <node>node002</node>
       </group>
       <group>
               <name>Compute</name>
               <image>Ubuntu_gutsy</image>               
               <override>Compute</override>
               <node>node003-node010</node>
       </group>
 </xml>
  

This is a 10-nodes cluster definition. The hostname of the image server is master1; the cluster has 2 login nodes (node001 and node002) that use the override called Login and 8 compute nodes (node003, node004, node005, node006, node007, node008, node009 and node010), that use the override called Compute.

Example 1. Example 1: distribute the passwd, shadow and group to all the nodes

Create the files:

 # cp -p /etc/passwd /var/lib/systemimager/overrides/all/etc/passwd
 # cp -p /etc/shadow /var/lib/systemimager/overrides/all/etc/shadow
 # cp -p /etc/group /var/lib/systemimager/overrides/all/etc/group
  

From master1 run the command:

 # si_pushoverrides -v all
  

Basically when you specify the global override all the nodes defined in cluster.xml are updated accordingly to the hierarcy of the overrides.

Example 2. Example 2: distribute different access.conf to Login and Compute nodes

Allow root to login on "Login" nodes only from the local domain, /var/lib/systemimager/overrides/Login/etc/security/access.conf:

  -:root:ALL EXCEPT LOCAL .localcluster.domain.org
  

Disallow direct login on "Compute" nodes for non-privileged users, /var/lib/systemimager/overrides/Compute/etc/security/access.conf:

  -:ALL EXCEPT root wheel:ALL
  

From master1 run the command:

  # si_pushoverrides -v Compute Login
  

Example 3. Example 3: close the second login node (node002) to non-privileged users

/var/lib/systemimager/overrides/node002/etc/security/access.conf:

 -:ALL EXCEPT root:ALL
 -:root:ALL EXCEPT LOCAL .localcluster.domain.org
  

From master1 run the command:

  # si_pushoverrides -v node002