在 /etc/passwd 文件内的字段清单：

As mentioned before, one can edit this file directly. But there are more elegant ways to apply changes, which are described in 第 8.4.3 节 “修改既有的帐号或密码”.

/etc/shadow 文件含以下的字段：

One can expire passwords using this file or set the time until the account is disabled after the password has expired.

The following commands allow modification of the information stored in specific fields of the user databases: passwd permits a regular user to change their password, which in turn, updates the /etc/shadow file (chpasswd allows administrators to update passwords for a list of users in batch mode); chfn (CHange Full Name), reserved for the super-user (root), modifies the GECOS field. chsh (CHange SHell) allows the user to change their login shell; however, available choices will be limited to those listed in /etc/shells; the administrator, on the other hand, is not bound by this restriction and can set the shell to any program of their choosing.

最后，chage (CHange AGE) 命令允许管理者变更密码的有效期 (-l 用户 选项列出现在的设置)。用 passwd -e 用户 命令强迫密码失效，要求用户登录时变更密码才能继续使用。

Besides these tools the usermod command allows to modify all the details mentioned above.

You may find yourself needing to “disable an account” (lock out a user), as a disciplinary measure, for the purposes of an investigation, or simply in the event of a prolonged or definitive absence of a user. A disabled account means the user cannot login or gain access to the machine. The account remains intact on the machine and no files or data are deleted; it is simply inaccessible. This is accomplished by using the command passwd -l user (lock). Re-enabling the account is done in similar fashion, with the -u option (unlock). This, however, only prevents password-based logins by the user. The user might still be able to access the system using an SSH key (if configured). To prevent even this possibility you have to expire the account as well using either chage -E 1user or usermod -e 1 user (giving a value of -1 in either of these commands will reset the expiration date to never). To (temporarily) disable all user accounts just create the file /etc/nologin.

You can disable a user account not only by locking it as described above, but also by changing its default login shell (chsh -s shell user). With the latter changed to /usr/sbin/nologin, a user gets a polite message informing that a login is not possible, while /bin/false just exits while returning false. There is no switch to restore the previous shell. You have to get and keep that information before you change the setting. These shells are often used for system users which do not require any login availability.

群组列在 /etc/group 文件内，类似 /etc/passwd 文件的纯文本数据库，包括以下的字段：

addgroup 与 delgroup 命令可以添加或删除群组。groupmod 命令修改群组的信息 (其 gid 或辨识码)。命令 gpasswd group 可变更群组的密码，gpasswd -r group 命令可删除群组的密码。