Because passwords play a central role in overall system security, all user accounts should have passwords. However, simply having a password is only the first step in making a user account secure. If the password is easy to figure out or guess, it will provide little real protection. In this section, we’ll look at characteristics of good and bad passwords. The considerations discussed here apply both to choosing the root password (which the system administrator chooses) and to user passwords. In the latter case, your input usually takes the form of educating users about good and bad choices.
The purpose of passwords is to prevent unauthorized people from accessing user accounts and the system in general. The basic selection principle is this: Passwords should be easy to remember but hard to figure out, guess, or crack.
The first part of this principle argues against imposing automatically-generated random passwords (except when government or other mandated security policies require it). Many users have a very hard time remembering them, and in my experience, most users will keep a written record of their password for some period of time after they first receive it, even when this is explicitly prohibited.
If users are educated about easier ways to create good passwords, and you take advantage of features that Unix systems provide requiring passwords to be a reasonable length, users can select passwords that are just ...