Before you upgrade an ESX host, back up the local VMFS file system. This backup ensures that you will not lose data during the upgrade.

Back up the files in the /etc/passwd, /etc/groups, /etc/shadow, and /etc/gshadow directories.

The /etc/shadow and /etc/gshadow files might not be present on all installations.

Back up any custom scripts.

Back up your .vmx files.

Back up local images, such as templates, exported virtual machines, and .iso files.