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How To Upgrade VMware ESXi 3.5 To 4.1 Update 1 (Free Version)

In this guide I will show you how to upgrade VMWare ESXi 3.5 to ESXi 4.1 Update 1 (Free Version) without going through the pain of reinstalling your host server and then restoring your VMs.

I was looking around for quite some time in regards to how to upgrade an ESXi 3.5 host to version 4.1 U1, and I could only find bits and pieces of information on upgrading ESX to version 4.0 or ESXi 4.0 to version 4.1, it was actually quite difficult to find any information on upgrading the free version of ESXi to the most recent release. So after some research and trail and error I finally managed a successful upgrade and to try and help people in the future that might want to do the same thing I wrote this guide.


Before we start the upgrade process there are a few requirements we need to meet first

First of all we need to download the update files on to your computer, to do this go to the VMware website and go to the Support & Downloads area, locate VMware ESXi (you will have to register with VMware if you have not done so already), from here you will be able to download the full isos or incremental update files.

The two files you will need are labeled:

Upgrade package from ESXi Server 3.5 to ESXi Server 4.0 Update 1

ESXi 4.1 Update 1 (upgrade ZIP from ESXi 4.0)

You will also have to go to the Drivers & Tools section and download the VMware vSphere CLI 4.0.


If you are using Windows 7 as your OS on the computer that you’re preforming the upgrade on there is an extra step that you will need to take as you will run into issues during the upgrade process. To get around this, use a VM application (VMware Workstation, VMware Server (Free), Oracle Virtualbox (Free)) and build a VM that can access the network that your ESXi Host is on, and make sure the OS is Windows XP SP2 or Windows Server 2003 SP2, and install the VMware vSphere Client v4.0 with Host Update Utility. You can get the client from another ESXi 4.1 Host or go to the VMware Website and get it from the Download Trial Software area. After that copy the 3.5 -> 4.0 Upgrade file to the VM.


Upgrade ESXi 3.5 To 4.0

The first thing you must do is prepare your ESXi host for the upgrade, open up your VMware ESX Client and log onto your host server, shut down all your virtual machines. Then place your host into maintenance mode by right-clicking on your host and selecting Enter Maintenance Mode, after it has entered maintenance mode you then want to close down the client.


Next open up the vSphere Host Update Utility, the first thing the application wants to do is download patches from VMware, click “yes” and allow it to download the information. Once the upgrade is done you will see the following screen below.


Select the host you wish to upgrade and click on Upgrade Host button, a window will appear prompting for an upgrade package, browse to the location of the 3.5 -> 4.0 upgrade package, the upgrade package will be validated then you will have to agree to VMware’s terms and conditions before you can proceed with the upgrade.


Next you will have to enter your hosts credentials, by default it puts “Root” in as user name, it’s best to use this account for the upgrade, so there are no issues with a user having the correct permissions. After you press Next the update utility runs a compatibility check on the host to make sure that you are currently running an older version of ESXi and that the upgrade is correct for your host server. Once this is done you’re shown a summary of the information. Press Finish to perform the upgrade.

You will see an upgrade progress screen appear which will show you the steps the server is taking during the upgrade.



Once the upgrade is done, your host server will reboot, After the reboot, verify that it has upgraded correctly by logging into the host and checking the version number on the summary page. If any issues occur during the upgrade, the upgrade will stop and tell you to view the logs, to view the logs log back into your host server, then click on File -> Export -> Export System Logs, choose a location then press OK. Once the files are saved open them up and look for where the process has failed




Before we proceed to the next upgrade phase, open up the host update utility again, click on the host server you just upgraded and then click on Scan for Patches, it will prompt you for your server’s user name and password, again the “root” account is recommended here, the utility will scan the host server and the VMware repository for patches, it will then show you how many patches are detected. Press “Patch Host” – this will download the latest firmware and VMware Tools for your host server.


Upgrade ESXi 4.0 To 4.1 Update 1

Now once you’re staisfied and you’re ready to move on to the next stage of the upgrade, if you have not done so already you need to install the VMware vSphere CLI tool that you downloaded earlier.

Again make sure all your VMs are shut down, and put your host server into maintenance mode, and open command prompt. Go to the CLI location’s bin Folder, by default this is C:\Program Files\VMware\VMware vSphere CLI\bin.


I find the quickest way to do this is to copy the upgrade file to the same location (as above) then run the following command:

image12 -server “IP ADDRESS” -i -b

You will be prompted for your host server’s username and password, press Enter and the upgrade process will begin.



Once the update has been completed you will be prompted to reboot your host server for the upgrade to take effect.

After you host server has started back up you should notice straight away the revision number has changed, and if you log into the vSphere Client you can confirm the change there as well.


That’s it, you have completed the upgrade, now if you want your VMs to get full functionality out of the host server, there are two things you need to do, 1. upgrade the VM’s hardware (right-click on the VM and click on Upgrade Hardware); 2. Upgrade the VM’s installation of VMware Tools (right -click and click on Install/Upgrade VMware Tools, Windows VMs will autorun the installer, Linux VMs will mount the installer to /media or an optical device mount point and you will have to manually run the installer).



I have had one issue occur on a couple of the upgrades I have performed in the past. After the upgrade from 3.5 -> 4.0, an issue has occured where you attempt to connect to the ESXi Host with the vSphere client, and the host server rejects the connection. This is caused by some custom configuration or setting, and there is a simple (but possibly annoying) fix. On your ESXi host, press F2, enter your username and password, then select Remove Custom Extensions; let the host restart, then select Reset System Configuration, unfortunately this brings your configuration back to default (your VMs will remain), but you will be able to log back in and reconfigure the host server.