You can install, upgrade, or migrate ESXi from a CD/DVD drive using a script that specifies the installation or upgrade options.

You can start the installation or upgrade script by entering a boot option when you start the host. You can also create an installer ISO image that includes the installation script. With an installer ISO image, you can perform a scripted, unattended installation when you boot the resulting installer ISO image. See Create an Installer ISO Image with a Custom Installation or Upgrade Script.


After you upgrade or migrate your host from ESX/ESXi 4.x to ESXi 5.x, you cannot roll back to your version 4.x ESX or ESXi software. Back up your host before you perform an upgrade or migration, so that, if the upgrade or migration fails, you can restore your 4.x host.

Before you run the scripted installation, upgrade, or migration, verify that the following prerequisites are met:

The system on which you are installing, upgrading, or migrating meets the hardware requirements. See ESXi Hardware Requirements.

You have the ESXi installer ISO on an installation CD/DVD. See Download and Burn the ESXi Installer ISO Image to a CD or DVD.

The default installation or upgrade script (ks.cfg) or a custom installation or upgrade script is accessible to the system. See About Installation and Upgrade Scripts.

You have selected a boot command to run the scripted installation, upgrade or migration. See Enter Boot Options to Start an Installation or Upgrade Script. For a complete list of boot commands, see Boot Options.


Boot the ESXi installer from the CD or DVD using the local CD/DVD-ROM drive.


When the ESXi installer window appears, press Shift+O to edit boot options.

ESXi Installer screen


Type a boot option that calls the default installation or upgrade script or an installation or upgrade script file that you created.

The boot option has the form ks=.


Press Enter.

The installation, upgrade, or migration runs, using the options that you specified.