[HOW TO] Unknown root / GRUB passwd prior to VMware vCSA upgrade

I was facing another really annoying issue recently which was quite new for me.

While looking for an acceptable solution I came across a website from Lingeshwaran Rangasamy which I do not want to hide as it describes how to fix it in a few steps.

Many kudos to @UnixArena. Hope he doesn’t mind my advertisement. Share the knowledge!

I was planning an horizontal upgrade from vCenter Server Appliance 6.0 U1 to the latest version 6.5 U1 using the VMware vCSA Upgrade tool. During the collection of all information I realized that the vCSA root password was not available ( don’t know the reason for that ).
But I knew that it is possible to reset the password when booting the vCSA GRUB boatloader and edit the boot option to get a root shell.
INFO: If the root password has expired but is documented you are able to renew it using the VAMI interface of the vCSA -> https://FQDN-of-vCSA:5480

Unfortunately it asks for a GRUB password to enable the root shell, which is, when not defined, the same as the root password. So in this case I was not able to access the GRUB boatloader to reset the root password.
As I was looking how to reset it anyway I stumpled across the blog of Lingeshwaran Rangasamy And there is a detailed instruction on how to reset both, the GRUB and root password:
I will not copy and paste the steps to my blog as he deserves all the credits to this solution but I thought it may be useful to spread this piece of information!
After the reset of the GRUB password I was able to reset the root password as described in the VMware KB article 2069041 and move on in upgrading the vCenter server appliance to the latest version without any further issues!
In short:

– Upgrade vCSA needs the root password during the migration.

– root password expired -> use VAMI interface to renew it

– root password not know -> use GRUB password and loader to reset it through the console

– Both password not known -> boot vCSA from CENT OS Live ISO ( minimal version is sufficient ) and reset the password ( LINK )
Hope this post will help someone facing a similiar situation. As I mentioned earlier: