密码更改¶

如果有旧密码，首先提示用户输入旧密码。加密这个密码然后和存储的密码进行比较。用户只有一次机会输入正确密码。允许超级用户略过这个步骤，以便更改忘记了的密码。

After the password has been entered, password aging information is checked to see if the user is permitted to change the password at this time. If not, passwd refuses to change the password and exits.

提示用户输入两次新密码。第二次和第一次进行比较，并且需要相同才能更改密码。

然后，测试密码的负责程度。一般来讲，密码应该包含 6 到 8 位字符，从下边的一个或多个集合中选择：

Care must be taken not to include the system default erase or kill characters. passwd will reject any password which is not suitably complex.

关于用户密码的提示¶

The security of a password depends upon the strength of the encryption algorithm and the size of the key space. The legacy UNIX System encryption method is based on the NBS DES algorithm. More recent methods are now recommended (see ENCRYPT_METHOD). The size of the key space depends upon the randomness of the password which is selected.

由于粗心地或处理选择密码，会危及密码的安全。由于这个原因，您不应该选择出现在词典中或者必须要写下来才能记住的密码。密码也不应该是一个名字、许可证号、生日或者街道号。所有这些可以用于猜测来损害系统安全。

You can find advice on how to choose a strong password on http://en.wikipedia.org/wiki/Password_strength