Before you upgrade an ESX host, back up the local VMFS file system. This 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 local images, such as templates, exported virtual machines, and .iso files.