the KB70100 that you posted in the community tell a solution to reset "admin" account but I need to reset the "root" account so do you have a KB that explain the step?.
ps. I still can't enter to single mode by use the following steps when I was the grub menu,
Instead of adding single to the kernel line, add init=/bin/bash and hit ENTER to go back to parent menu. (ESC will revert your change!). Then hit b to boot this kernel line.
This will drop you directly into a shell. File system will be mounted read-only, so you have to make it writeable before you can reset the password.
# mount -o remount,rw /
You should see "passwd: all authentication tokens updated successfully."
Because you bypassed original init service you have to take care when rebooting the appliance as normal shutdown/reboot scripts won't work.
First make sure that all data is written to HDD with "sync", then force reboot with parameter -f:
# reboot -f
Single user mode won't help you here because it will still ask for root password.
In 7.8.2 and higher (MLOS 3)
1. At the GNU GRUB boot menu select McAfee Web Gateway and press e to edit.
2. Go to the line that starts with linux and append init=/bin/bash at the end of the line.
3. Press Ctrl-x or F10 to boot.