How many characters should your password be for a root pw for a server?
8+ Characters of mixed case with no dictionary based word is a good start for the root password.
Brute force attacks will often use a dictionary, but can also attempt mutations of the dictionary word.
All these passwords are 8 characters; they are all very poor choices:
With less than 8 it is possible for an offline attack to try every possible combination; depending on the system speed. If you want to be sure make up something mixed with 10 characters.
I think you need at least 8 characters. I last read from somewhere, 14 characters onwards are harder to crack. Including lower case, upper case, numbers and special characters is a must. You can also refer to this guide on how to create a strong password http://www.itscolumn.com/2011/04/how-to-create-a-strong-password/
I use 256 character passwords where possible...then again I don't manually type them.
If I'm feeling really paranoid I use a two-factor authentication with a yubi key.