How To Upgrade VMware ESXi 3.5 To 4.1 Update 1 (Free Version) - Page 2
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:
vihostupdate.pl -server "IP ADDRESS" -i -b upgrade-from-esxi4.0-to-4.1-update01-348481.zip
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.