Restarting the Management agents on an ESX or ESXi Server (May Solve all below symptoms)

Symptoms / Problems 

• Cannot connect ESX to VirtualCenter
• Cannot connect ESX to vCenter Server
• Cannot connect directly to ESX Server from the VMware Infrastructure Client
• Cannot connect directly to the ESX Server from the vSphere Client
• You cannot stop or start a virtual machine
• A virtual machine is shown as running in VirtualCenter when it is not
• VirtualCenter shows the error:
  
  
  
  Virtual machine creation may fail because agent is unable to retrieve VM creation options from the host

Purpose 

For troubleshooting purposes, it may be necessary to restart the management agents on your ESX Server. This article provides you with the steps to restart the management agents (mgmt-vmware and vmware-vpxa) directly on ESX or ESXi.

This article applies ESX 3 and ESX 4, as well as ESXi 3 and ESXi 4.

Caution: Restarting the management agents may impact any tasks that may be running on the ESX or ESXi host at the time of the restart. For more information about identifying tasks running on an ESX or ESXi host, see Collecting information about tasks in VMware ESX and ESXi (1013003).

Resolution :

Click below --> "Read More" for Full Article (How to restart Mgt agent on ESX & ESXi)..

Restarting the Management agents on ESX

To restart the management agents on ESX host:

1. Log in to your ESX Server as root from either an SSH session or directly from the console of the server.
2. Type service mgmt-vmware restart.
   
   
   Caution: Ensure Automatic Startup/Shutdown of virtual machines is disabled before running this command or you risk rebooting the virtual machines. For more information, see Restarting hostd (mgmt-vmware) on ESX Server Hosts Restarts Hosted Virtual Machines Where Virtual Machine Startup/Shutdown is Enabled (1003312) and Determining whether virtual machines are configured to autostart (1000163).
3. Press Enter.
4. Type service vmware-vpxa restart.
5. Press Enter.
6. Type logout and press Enter to disconnect from the ESX host.

If this process is successful, it appears as:

[root@server]# service mgmt-vmware restart
Stopping VMware ESX Server Management services:
VMware ESX Server Host Agent Watchdog [ OK ]
VMware ESX Server Host Agent [ OK ]
Starting VMware ESX Server Management services:
VMware ESX Server Host Agent (background) [ OK ]
Availability report startup (background) [ OK ]
[root@server]# service vmware-vpxa restart
Stopping vmware-vpxa: [ OK ]
Starting vmware-vpxa: [ OK ]
[root@server]#

Note: If there are failures listed:

• The most common reason for a stopping task to fail is that the service is not started.
• If a starting task fails for the mgmt-vmware service, see Troubleshooting the VMware ESX Server Management Service when it will not start (1003561).
• If a starting task fails for the vmware-vpxa service, see Troubleshooting the VirtualCenter Agent Service when it will not start (1006128).

Restarting the Management agents on ESXi

To restart the management agents on ESXi:

1. Connect to the console of your ESXi Server.
2. Press F2 to customize the system.
3. Login as root.
4. Using the Up/Down arrows navigate to Restart Management Agents.
5. Press Enter.
6. Press F11 to restart the services.
7. When the service has been restarted, press Enter.
8. Press Esc to logout of the system.

If starting or stopping the management agent fails try restarting it a second time. If it still fails please file a support request with VMware Support.

(Source - VMware KB Article: 1003490)