8 Tips for Troubleshooting VMware vSphere

This 3-part series talks about 8 tips for working with vSphere. Some of the topics are logging in via Command Line TSM, dealing with connection problems using SSH to an ESXi host, and important log files and their locations. In addition, some of the tips look at dealing with performance-related issues, such as networking.

Logging in via Command Line TechSupportMode

By default, the ESXi host does not have SSH enabled on the host. There are occasions when you need to login via command line to solve problems, but this can be easier said then done. We’re going to look at a method called Tech Support Mode, which is a hidden or unsupported method to gain command line access to the host. Essentially, you’re enabling the SSH Daemon directly on VMware’s proprietary version of Unix where the hypervisor is running, enabling the root user to either log in directly on the console of the ESXi host, or log in remotely via SSH.

ESXi 3.5 or 4.0

  1. To start, check the techSupportMode setting. To make sure this setting is correct, log into the vCenter Server, using the vSphere Client (depending on version, this may not be necessary)
  2. Select the ESXi host and choose the Configuration tab, then select Advanced Settings in the Software panel. In the left pane, click VMkernel.
  3. Enable VMkernel.Boot.techSupportMode and click OK. Reboot the ESXi host if you need to enable technical support mode
  4. To use Tech Support Mode, log in to the ESXi host using the Direct Console User Interface (DCUI)
  5. Press Alt+F1 to display the console screen
  6. Enter by typing unsupported to start the Tech Support Mode process. Note that no text will appear on the console window
  7. Enter the password for the root user, and you should than see an SSH prompt

ESXi 4.1

First method from the Direct Console User Interface (DCUI)

  1. Hit Alt+F1, if TSM is enabled, log in with root credentials, else
  2. Once the DCUI screen appears, press F2 and login as root to enable the TSM
  3. Navigate down the screen and choose Troubleshooting Options, and press enter
  4. Troubleshooting Options provides additional options for TSM in ESXi 4.1

 <Enable/Disable> Local Tech Support — Access command line via Alt+F1 on the console.

<Enable/Disable> Remote Tech Support (SSH) — SSH access on the console of the ESXi host.

Modify Tech Support Timeout — Tech Support Mode will be disabled after a certain amount of time.

Second Method from the vSphere Client:

  1. From the vSphere Client, select the host and click Configuration tab
  2. Then choose Security profile and Properties
  3. Here you can enable Local Tech Support as well as Remote Tech Support (SSH). They’re enabled if the Daemon is running and disabled if the Daemon is Stopped. If you want to enable either mode, highlight the mode, then choose Options
  4. Now you can modify the Startup Policy or change the Service to Start, then click OK

Access the local TSM (Local Tech Support):

At the main DCUI screen, press Alt+F1, login.

Access the remote TSM:

Use a utility, such as putty to establish an SSH connection.

Connection Problem Using SSH to an ESXi 4 host

In vSphere 4, VMware started using the Dropbear SSH server. This server isn’t enabled by default on an ESXi server. Check to make sure SSH is running on the ESXi host. On the ESXi host, log directly into the console of the host as root. From a command line prompt type# ps | grep dropbear

You should get a response similar to this:

295811 295811 dropbearmulti        dropbear

which states that the dropbear version of SSH is running on the system. If there isn’t a response, then restart the SSH Daemon.

  1. Connect to the console of your ESXi host.
  2. Press F2 to customize the system
  3. Login as root
  4. Using the Up/Down arrows navigate to Restart Management Agents.

If attempting to restart the SSH Deamon manually fails, reboot the ESXi host. You might have to check tip #1 to see if SSH is enabled on the host.

We’ll look at more troubleshooting methods next week.

This post is excerpted and reused with permission from 8 tips for Troubleshooting VMware vSphere

Related Courses

VMware vSphere: Install, Configure, Manage [V4.1]
VMware vSphere: Troubleshooting [V4x]
VMware vSphere: Manage for Performance [V4x]
VMware vSphere: Advanced Fast Track [V4.x]

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