Removing the SCOM 2012 R2 agent on a core edition

Recently I reinstalled the whole SCOM setup in my lab. Just because I wanted to test with the latest versions like R2 and needed to use the 180 trial license for that. This left me with a problem. Some of my servers kept reporting to my old SCOM server although it was obviously down. Re-adding the server to the current server didn't work. In the logs, I saw the following messages reappear (scom being my old server)

The description for Event ID 21006 from source OpsMgr Connector cannot be found. Either the component that raises this event is not installed on your local computer or the installation is corrupted. You can install or repair the component on the local computer.

If the event originated on another computer, the display information had to be saved with the event.

The following information was included with the event:

scom

5723
10060L
A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.

So I decided to remove it from SCOM and then manually uninstall the agent. One problem, one of the servers is a core edition. Good lucking launch appwiz on that one. Luckily, it is quite easy to find out how you need to uninstall it. Launch regedit and go to

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\

For every installed program, there should be a subkey under which you can see the DisplayName and the UninstallString.

Alternatively, you can use the following script:

$(Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\') | % { Write-host ("Soft : {0} `n`t {1}" -f $_.getvalue("DisplayName"),$_.getvalue("UninstallString")) }

It should output something like this

Soft :

Soft : Microsoft Visual C++ 2008 Redistributable - x64 9.0.30729.4148
         MsiExec.exe /X{4B6C7001-C7D6-3710-913E-5BC23FCE91E6}
Soft : VMware Tools
         MsiExec.exe /X{4D80C805-67C3-4525-A7BA-DC43215E9167}
Soft : Microsoft Monitoring Agent
         MsiExec.exe /I{786970C5-E6F6-4A41-B238-AE25D4B91EEA}

 So to uninstall the agent, first stop the service, just to be sure:

 net stop healthservice

 Then Uninstall the agent. I used the /X flag instead of the /I flag

 MsiExec.exe /X{786970C5-E6F6-4A41-B238-AE25D4B91EEA}

Btw at first, the command didn't want to do anything, rebooting the server helped. A GUI should appear requesting if you are sure you want to uninstall.

Then I deleted the directories under program files just to be sure that no residue was left on the filesystem:

rmdir "C:\Program Files\System Center Operations Manager" /s

rmdir "C:\Program Files\Microsoft Monitoring Agent" /s

Redeployed and let's hope I won't see those nasty error messages re-appear