To update to the latest version of vSphere, VMware presents in the Download area packages to use with vCenter Update Manager or vihostupdate to upgrade from ESXi 4.0 or ESXi 3.5.
I had the intention to update my current ESXi 4.1 hosts with the vihostupdate utility and was wondering how to determine the content of a package called: update-from-esxi4.1-4.1_update01.zip. The answer is in the vSphere Command-Line Interface Installation and Scripting Guide. For my own convenience, I have logged the whole process in this post.
IMPORTANT: In case you run another version of ESXi, you have to download one of the other packages, the steps are similar.
Note: vihostupdate performs the actions on one host at a time and you have to provide connection info with each command. In this example, the hostname is ml110g6.
Before you start, the host must be in maintenance mode before you can install patches. You can check with this command.