Managing Serviceguard Sixteenth Edition, March 2009

cmmodpkg -e -t pkg1
You will see output something like this:
package:pkg3|node:node2|action:failing
package:pkg2|node:node2|action:failing
package:pkg2|node:node1|action:starting
package:pkg3|node:node1|action:starting
package:pkg1|node:node1|action:starting
cmmodpkg: Command preview completed successfully
This shows that pkg1, when enabled, will “drag” pkg2 and pkg3 to its primary node,
node1. It can do this because of its higher priority; see “Dragging Rules for Simple
Dependencies” (page 168). Running the preview confirms that all three packages will
successfully start on node2 (assuming conditions do not change between now and
when you actually enable pkg1, and there are no failures in the run scripts).
NOTE: The preview cannot predict run and halt script failures.
For more information about package dependencies and priorities, see “About Package
Dependencies” (page 166).
Using cmeval
You can use cmeval to evaluate the effect of cluster changes on Serviceguard packages.
You can also use it simply to preview changes you are considering making to the cluster
as a whole.
You can use cmeval safely in a production environment; it does not affect the state of
the cluster or packages. Unlike command preview mode (the -t discussed above)
cmeval does not require you to be logged in to the cluster being evaluated, and in fact
that cluster does not have to be running, though it must use the same Serviceguard
release and patch version as the system on which you run cmeval.
Use cmeval rather than command preview mode when you want to see more than
the effect of a single command, and especially when you want to see the results of
large-scale changes, or changes that may interact in complex ways, such as changes to
package priorities, node order, dependencies and so on.
Using cmeval involves three major steps:
1. Use cmviewcl -v -f line to write the current cluster configuration out to a
file.
2. Edit the file to include the events or changes you want to preview
3. Using the file from Step 2 as input, run cmeval to preview the results of the
changes.
For example, assume that pkg1 is a high-priority package whose primary node is
node1, and which depends on pkg2 and pkg3 to be running on the same node. These
lower-priority-packages are currently running on node2. pkg1 is down and disabled,
and you want to see the effect of enabling it.
326 Cluster and Package Maintenance