Many of the linux distributions, especially the
live CDs or DVDs, boot automatically into the
desktop, without the person initiating the running of the linux distro having to inter username and a
password.

Then, there are those live CDs or DVDs that demand a password at the very beginning, sometimes giving the password in the announcement of the distro's
availability. But, then, you meet those that do
not give a password. So if you are not already into the desktop without the password, just what
do you have to do to get the devil to work?

Some of them use the word root as password too

Agree with TroN - most have passwords like user and root, or guest and root. Those are always worth a try.

slax uses username root, password toor.