If You set password only once during the installation and later on decided to change your password it can be confusing. What you have to know is during installation it sets the same password for your user and for root.
For example you enter the same password when you install some thing as root:
$ sudo apt-get install audacious
and when connecting to your machine via ssh as user:
$ ssh firstname.lastname@example.org
If you want to keep it that way with new password, you have to change it for both user and root:
$ sudo passwd
If you wondering what is a good password , check this link:
After playing with this site a come to conclusion that it can be two types of good passwords:
- relativity short password (9 characters) containing combination of lower case letters, capital letters, numbers and symbols. What could be harder to remember.
- longer password (18 characters) containing only lower case Latin letters, but in this case You can use sentence in foreign language. It can be much easier to remember. Perhaps you can use a bit longer sentence in English as well.