I have seen some people google for the default root password for sigma designs boards and they ended up in this blog without any answer. So I’ll provide some kind of answer.
In the serial port console, once you get to the username/password prompt, the root password is… there is none, just press “Enter”. This is the default behavior in Sigma Designs SDK, it’s quite possible the root password has been changed for the device you are trying to access.
In case telnet or ssh is enabled, you may try one of the default users in /etc/password, that may not have been disabled by the development team e.g. ftp, man, nobody,default, etc… and try to login without password, by just pressing “Enter” at the password prompt. Once you are logged-in as a normal user, type “su” to become super user, press “Enter” if you are being asked for a password.