I have a client that has been upgraded to vCenter 6.5 appliance. However when they attempt to log into the Web Interface they get the "Flash is required" message. Is there a simple switch or command to log into the html5 vcenter portion?
try https://<vcentername or ip>/ui
Should that allow me to bypass the "Flash" portion and allow me to log into vCenter directly?
yes.
the direct link to the webclient (flash) is <vcenter>/vsphere-client, to html5 is <vcenter>/ui
