How many times have you open SOLMAN_SETUP -> Managed system configuration just to find your Diagnostics Agent does not show up in the list?..
There is a number of reasons why diagnostics agents do not get registered properly or fail to start during install and then registration is missing or incomplete, in any case there is a few options to get them back on track (including re-install), but assuming the installation was successful the quickest way to recover the Diagnostics Agent and get it talking to both SLD and SOLMAN is to re-register them.
I've found the best way to do this is to follow this steps,
First, the first... Stop the diagnostics agent
Go to the script directory /usr/sap/<DA_SID>/<DA_instance>/script
Register with the SLD using command,
./smdsetup.sh sldconf hostname:"<sld_host.fqdn>" port:"<sld_port>" user:"<username>" pwd:"<password>"
Immediatly after, register with solman using command,
./smdsetup.sh managingconf hostname:"sapms://<solman_host.fqdn>" port:"<port>" user:"<username>" pwd:"<password>"
Finally, restart your Diagnostics Agent
Sometimes, if the initial registration ended badly the diagnostics agent servername can also be missing which leave you with an error similar to "Server name assignment'' on the agent failed mainly caused by the name of host missing from the agent. This can be corrected by using the following command,
./smdsetup.sh changeservername servername:"<diagnostic_agent_host>"
These few commands should be a good resource to deal with rebel diagnostics agents during Managed System Configuration.
Love to hear your comments