Linux 用户管理

一、简便方法:直接编辑文件

1、编辑/etc/passwd

Understanding fields in /etc/passwd

The /etc/passwd contains one entry per line for each user (or user account) of the system. All fields are separated by a colon (:) symbol. Total seven fields as follows.

Generally, passwd file entry looks as follows (click to enlarge image):

(Fig.01: /etc/passwd file format - click to enlarge)

1. Username: It is used when user logs in. It should be between 1 and 32 characters in length.
2. Password: An x character indicates that encrypted password is stored in /etc/shadow file.
3. User ID (UID): Each user must be assigned a user ID (UID). UID 0 (zero) is reserved for root and UIDs 1-99 are reserved for other predefined accounts. Further UID 100-999 are reserved by system for administrative and system accounts/groups.
4. Group ID (GID): The primary group ID (stored in /etc/group file)
5. User ID Info: The comment field. It allow you to add extra information about the users such as user's full name, phone number etc. This field use by finger command.
6. Home directory: The absolute path to the directory the user will be in when they log in. If this directory does not exists then users directory becomes /
7. Command/shell: The absolute path of a command or shell (/bin/bash). Typically, this is a shell. Please note that it does not have to be a shell.

2、编辑/etc/group

It stores group information or defines the user groups i.e. it defines the groups to which users belong. There is one entry per line, and each line has the following format (all fields are separated by a colon (:)

cdrom:x:24:vivek,student13,raj
_____ _  _      _____
|    |  |        |
|    |  |        |
1    2  3        4

Where,

1. group_name: It is the name of group. If you run ls -l command, you will see this name printed in the group field.
2. Password: Generally password is not used, hence it is empty/blank. It can store encrypted password. This is useful to implement privileged groups.
3. Group ID (GID): Each user must be assigned a group ID. You can see this number in your /etc/passwd file.
4. Group List: It is a list of user names of users who are members of the group. The user names, must be separated by commas.

3、编辑/etc/shadow

(Fig.01: /etc/shadow file fields)

1. User name : It is your login name
2. Password: It your encrypted password. The password should be minimum 6-8 characters long including special characters/digits
3. Last password change (lastchanged): Days since Jan 1, 1970 that password was last changed
4. Minimum: The minimum number of days required between password changes i.e. the number of days left before the user is allowed to change his/her password
5. Maximum: The maximum number of days the password is valid (after that user is forced to change his/her password)
6. Warn : The number of days before password is to expire that user is warned that his/her password must be changed
7. Inactive : The number of days after password expires that account is disabled
8. Expire : days since Jan 1, 1970 that account is disabled i.e. an absolute date specifying when the login may no longer be used

二、使用命令进行操作

略……………