This procedure should be performed right after deploying NSX-T manager to avoid facing a terrible problem (according to VMware’s) in case that you forget, or loose the password of “root” account.
If the configuration is not performed after deploying the appliance and you forget the root password, resetting the root password is not possible.
NSX-T 2.4 installation guide – Page 33.
Configure NSX-T Data Center to Display the GRUB Menu at Boot Time
1- Log in to the VM as root.
2- Change the value for the parameter GRUB_HIDDEN_TIMEOUT in the /etc/default/grub file.
3- Update the GRUB configuration.
4 (Optional) Change the GRUB password in the /etc/grub.d/40_custom file.
The default password is VMware1.