Take a snapshot or backup of the vCenter Server Appliance before proceeding.
Note: If the vCenter Appliance is on the same ESXi hosts it manages. Connect directly to the ESXi host that it is located on to perform these steps. Reboot the vCenter Server Appliance.
After the VCSA Photon OS starts, press the e key to enter the GNU GRUB Edit Menu. Locate the line that begins with the word Linux.
Append this entries to the end of the line:
Press F10 to continue booting.
Once booted into the CLI run the command mount:
-o remount,rw /
In the Command prompt, enter the command:
Provide a new root password (twice for confirmation). Unmount the filesystem by running this command (yes, the unmount command is umount - it's not a spelling error):
Reboot the vCenter Server Appliance by running this command:
Confirm that you can access the vCenter Server Appliance using the new root password.