Last week I saw this how-to guide on Eric Sloof’s website and didn’t get round to posting it until today.
It’s a great step-by-step guide on upgrading ESX 4.0 to ESX 4.1 via the command line utility.
If your ESX servers hosting the virtual machine with vCenter (local storage) and you cannot use the vSphere Host Update utility to upgrade ESX 4.x hosts. This utility is only for standalone ESX 3.x and ESXi hosts. A standalone host is an ESX host that is not managed by vCenter Server. Eric found another way to upgrade this ESX host exactly because of this. The resolution for this problem is the esxupdate Command-Line Utility available in the service console.
The first step is to download the following zip files from VMware’s website and copy the files to the service console:
pre-upgrade-from-ESX4.0-to-4.1.0-0.0.260247-release
upgrade-from-ESX4.0-to-4.1.0-0.0.260247-release.zip
The second step is to install the pre-upgrade using esxupdate, this can be done without a reboot and without maintenance mode.
esxupdate –bundle=pre-upgrade-from-ESX4.0-to-4.1.0-0.0.260247-release.zip update
Now you have to put you ESX host into maintenance mode, this can also be done with the command line otherwise you will get this message: Description – Maintenance mode is not enabled or could not be determined.
vimsh -n -e /hostsvc/maintenance_mode_enter
We can finally upgrade the ESX host to 4.1 with the following command line:
esxupdate –bundle=upgrade-from-ESX4.0-to-4.1.0-0.0.260247-release.zip update
The update is completed successfully, but the system needs to be rebooted for the
changes to be effective.
Reboot… vimsh -n -e /hostsvc/maintenance_mode_exit Done 
After finishing this article Eric discovered a similar one written by Tomi Hakala over at vReality!
