You could install ESXi to a USB flash device and then access iSCSI or NFS storage on another host. You won't be able to create a local datastore without another hard drive or without formatting the existing one.
ESXi provides a pretty minimal console interface and you can't interact with VMs running on the host directly at the console. If that's a requirement for you then you might want to look at VMware Player, Workstation or Server.
Is your machine has a option of boot from USB.
Then you can try this insert a USB flash supported by VMware refer the below link for preparing usb flash drive for esxi installation.
Once you have done with the formating.
burn the ESXI installable on a cr-rom and boot with the cd and proceed installation.
Easy and good to use.
download vmware workstation for linux - i am not sure if that support ubuntu linux.
create a virtual machine install esxi and start you testing,
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