The ESXi CLI upgrade method is an alternative to the interactive installer. With the interactive installer method, the ESXi needs to boot off the ISO image to performing the upgrade, meaning that you would need physical access to the server or access to its IPMI interface.

However, with the CLI method, the upgrade can be performed while the ESXi is up and running. This is done via an SSH session to the host and only requires a single reboot. You cannot use an ESXi Installer ISO image to perform the CLI installation – this can only be achieved using an offline bundle. An offline bundle can have multiple image profiles, and one of them needs to be specified to perform the upgrade. You will learn more about image profiles in Chapter 11, Building Custom ESXi Images Using Image Builder.