Here are descriptions of (Web hosting comparison) the file entry fields,
Here are descriptions of the file entry fields, with examples from the line in Figure 3-6: 1. The login ID (username, or account name). This information corresponds to the /etc/passwd entry for the account. beginningunix:$1$cth3s70B$Sol7rv9u.UyKtEyZ0HP.V.:12736::9999:::: 2. The encrypted version of the password (which can be 13 or more characters depending on the Unix implementation). Because this file is readable only by root, the passwords are more protected than if they were in the openly readable in /etc/passwd file. If this field is blank, the user is not required to enter a password a very dangerous situation, because only the account name need be discovered for the system to be compromised. There are ways to lock an account (prevent anyone from using it) with this field as well, depending on the version of Unix. On some systems, for example, NP in this field means that the user cannot actively log in to the account, but must log in with his own account and then use sudo (discussed later in this chapter). You can also put a * (*LK* for Solaris) to indicate that the account is locked. beginningunix:$1$cth3s70B$Sol7rv9u.UyKtEyZ0HP.V.:12736::9999:::: 3. The number of days from January 1, 1970, until the password was changed. This is used in conjunction with the other fields to determine if the account and password are still valid and if the password requires updating. beginningunix:$1$cth3s70B$Sol7rv9u.UyKtEyZ0HP.V.:12736::9999:::: The January 1, 1970, date represents what is called the epoch. It s a date picked out by the creators of Unix as a good start time. 4. The minimum number of days before the user can change his password again. This allows the system administrator to protect the user from changing his password too soon after the previous change, reducing the chance an attacker can change the password if he finds it. This field is also used for administrative functions such as password propagation between systems. In this example, the field is blank: beginningunix:$1$cth3s70B$Sol7rv9u.UyKtEyZ0HP.V.:12736::9999:::: 5. The maximum number of days the password is valid before requiring a change. The administrator uses this field to enforce password change policies and to reduce the likelihood that a malicious entity can use brute force (continually trying passwords) to crack the password, which can take a significant amount of time, depending on how good the password is. beginningunix:$1$cth3s70B$Sol7rv9u.UyKtEyZ0HP.V.:12736::9999:::: 6. The number of days the user is warned before password expiration. It is a good practice to give each user warning that her password is going to expire, so that she has the opportunity to change it at a convenient time before its expiration. If the user fails to change her password in the given amount of time, she could be locked out of the system until the system administrator can intervene. In this example, the fields 6 9 are blank, as they are in most systems: beginningunix:$1$cth3s70B$Sol7rv9u.UyKtEyZ0HP.V.:12736::9999:::: 36 Chapter 3
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