I have an issue with the "root" account on SDDC Manager. Even when the password is correct it says "Authentication failure".
After changing the password from grub menu as well, it gives the same error. I logged in to SDDC Manager via "vcf" account and tried to switch to "root" account but doesn't work.
You will 1st have to unlock the account run the below command .
if you have already tired the above then , there is one know issue in VCF 4.2 & 4.2.1 which is fixed in VCF 4.3
try the below
pam_tally2 -u root