Hi,
A new security feature has been introduced with vCenter 5.5. Now by default, there is a password expiration. So the administrator account (root) password will expire automatically after 90 days of powering on the VCSA. That's a good idea 
but sometimes you forgot good security practices...
To unlock your root account :
1) Reboot your VCSA
2) Interrupt boot at grub level
3) Type p
4) Enter password (default=vmware)
5) Edit line started by kernel (type e)
6) At endline, add init=/bin/bash
7) Press enter then b (=boot)
If it's ok, your are root
😎 Edit /etc/shadow
9) For the root user account, delete "x" in the 2nd field and delete the numeric value in the 5th field (default value is 90)
10) Save your file ( you could have a warning with a readonly file, but the file is really written)
11) Reboot
12) Try to log on https://@IP or FQDN_VCSA5.5:5480 with your root account (login=root password=vmware)
13) Enjoy :smileygrin:
Optional (but recommended)
14) Modify your settings, enable password expires and configure a smtp server in order to be alerted
