The user is first prompted for their old password, if one is present. This password is then encrypted and compared against the stored password. The user has only one chance to enter the correct password. The super user is permitted to bypass this step so that forgotten passwords may be changed.
After the password has been entered password aging information is checked to see if the user is permitted to change their password at this time. If not, passwd refuses to change the password and exits.
The user is then prompted for a replacement password. This password is tested for complexity. As a general guideline, passwords should consist of 6 to 8 characters including one or more from each of following sets:
Care must be taken not to include the system default erase or kill characters. passwd will reject any password which is not suitably complex.
If the password is accepted, passwd will prompt again and compare the second entry against the first. Both entries are require to match in order for the password to be changed.
Compromises in password security normally result from careless password selection or handling. For this reason, you should select a password which does not appear in a dictionary or which must be written down. The password should also not be a proper name, your license number, birth date, or street address. Any of these may be used as guesses to violate system security.
Your password must easily remembered so that you will not be forced to write it on a piece of paper. This can be accomplished by appending two small words together and separating each with a special character or digit. For example, Pass%word.
Other methods of construction involve selecting an easily remembered phrase from literature and selecting the first or last letter from each. An example of this is
which produces
You may be reasonably sure few crackers will have included this in their dictionary.