A number of customers have been reporting the message: “Failed to install the VirtualCenter Agent Service“, when trying to connect an ESX host to virtual center, often after upgrading to ESX 3.0.2 and VC 2.0.2. In all the cases I have come across these reason seems to be that /tmp/vmware-root does not exist. This directory has to exist for the agent install process. To remedy this you can-

1. Login to ESX Server via ssh client as root user
2. cd /tmp
3. mkdir vmware-root
4. Try re-connecting the host to Virtual Center

Apparently there is a cron job that is removing this directory whenever it runs.Here is another method:

1. Disable HA. Otherwise, the virtual machines might be forcibly powered down by step 2.
2. At the service console, issue
   service mgmt-vmware restart
3. At the service console, issue
   service vmware-vpxa restart
4. Reconnect the virtual machines to VirtualCenter.
5. Attempt to re-enable HA within VirtualCenter. If this doesn’t work, this means that vpxa did not install properly.
6. At the service console, issue
   rpm -qa | grep vpxa
7. At the service console, issue “rpm -e” on the rpm file that displayed in the previous command.
   rpm -e
8. Reconnect the virtual machines in the usual manner within VirtualCenter.
9. Re-enable HA.