Thursday, October 23, 2008

ESXi and the undocumented Tech Support Mode

KB Article 1003677 talks about this thing called Tech Support Mode. This is a command-line interface that can be used with VMware ESXi Hosts to assist with the troubleshooting process.

For information on the Architecture of VMware ESXi, please see the Architecture of VMware ESXi Whitepaper which goes into great detail explaining how ESXi is designed and how it differs from classic ESX Server.

When you use Tech Support Mode, you have access to a command line shell that allows you to do things like restart services, but this mode should ONLY be used while working with VMware Technical Support to troubleshoot an issue.

To use Tech Support Mode:

  1. Log in to your ESXi host at the console.
  2. Press Alt+F1 to switch to the console window.
  3. Enter unsupported to start the Tech Support Mode login process. Note that no text will appear on the console window.
  4. Enter the password for the root user. Tech Support Mode is now active.
  5. Complete tasks in Tech Support Mode.
  6. Enter the command exit to exit Tech Support Mode.
  7. Press Alt+F2 to return the server to DCUI mode.

After logging in to Tech Support Mode, you will see the following where you can run the commands:


Some people equate Tech Support Mode with the Service Console of classic ESX Server. There are some that think ESXi relies on Tech Support Mode for Management and that ESXi is no different than classic ESX Server. This is not true. This "busybox" interface of ESXi is NOT necessary for ESXi to function. In fact you can easily disable Tech Support mode, and ESXi will run just fine.

To disable Tech Support Mode:

  1. Connect VMware Infrastructure Client (VI Client) to an ESXi host or a VirtualCenter Server.
  2. Browse to a host in the inventory list.
  3. Click the Configuration tab.
  4. Click the advanced Settings link.
  5. Click "VMkernel" in the left-hand side pane.
  6. In the list of parameters, deselect VMkernel.Boot.techSupportMode.
  7. Restart the ESXi host. Before restarting the host, you should shut down virtual machines on that host or migrate them to another host using VMotion or cold migration.

With Tech Support Mode disabled, you can press Alt+F1, and switch to the console window, but when you type in unsupported, you will NOT be able to enter the special Tech Support Mode (it has been disabled and is not running) as shown by the following:


Since you can run ESXi with Tech Support Mode disabled, you can see that ESXi doesn’t rely on this, and it is nothing like the Console OS of classic VMware ESX 3.

1 comment:

Anonymous said...

It doesn't rely on it when the vmkernel has been launched, but it does need to be there to launch it in the first place... So I would say it does rely on busybox!