User/user group summary in Linux

1: What is a user? What is a user group?

User: Is the identity of the system users

User group: A collection of users with the same characteristics, sharing a certain power

2: Types of users and user groups?

User:

A. Administrator root: A user with all rights to the system, with a UID of 0.

B. Ordinary users: That is, the general user, the use of the system has limited access to the UID of 1000 after.

C. System users: To ensure that the system operation of users, generally do not provide password login system, the UID is between 1~999. Set in/etc/login.defs

User groups:

A. Common user groups: can join multiple users

B. System group: Generally add some system users

C. Private groups (also known as basic groups): When a user is created, if the owning group is not specified for it, a private user group is defined for it, and the name is the same as the user name.

Note: A private group can become a normal user group, and when other users are added to the group, it becomes a normal group

3: Files related to users and user groups?

User:
/ETC/PASSWD # # #用户信息
User: Password: uid:gid: Description: Home directory: User-used Shell
/etc/shadow # # #用户认证信息
User: Password: Last password modified this time: Minimum validity: Maximum validity: Warning Period: Inactive period: Account expiration date

/etc/skel/.* # # #用户骨架文件

User groups:

/etc/group # # #组信息
Group name: Group password: Group ID: Additional Group member
/etc/gshadow # # #组认证信息
/home/username # # #用户家目录

4: View the user's ID

ID parameter
-U user # #用户uid
-G User # #用户初始组id
-G # #用户所有所在组id
-N # #显示名称而不是id数字
-A # #显示所有信息
5: Creation and deletion of users and groups:
Useradd Zpy #建立用户, a private group is typically created at the same time as the user is established
Userdel-r zpy #-r Deleting a user's profile
Groupadd zpy #建立组
Groupdel zpy #因为组没有文件, so do not add-r
Creation and deletion of users and groups:
Useradd zpy
Userdel-r zpy #-r Delete a user's profile note: When you want to delete the name of the username and a group, if the group and this file, no relationship, then will not delete this group
Groupadd zpy
Groupdel zpy #因为组没有文件, so do not add-r
Useradd-p Mima User #指定用户密码
-U 1111 User #指定uid为1111
-G 1111 User #指定gid if this group exists
-C "Interpreting content" #指定解释内容
-d/home/file User #指定家目录

Note: Beginners must pay attention, the above for the establishment of the user when the way to specify some information, if you want to change, do not delete this user, re-establish by the way to specify, or use the following usermod instructions to make changes, after establishing the user, you can no longer establish

6: Changes to user information

Usermod parameter User
-L # #更改用户名称
-U # #更改uid
-G # #更改gid
-G # #更改附加组
-ag # #添加附加组
-C # #更改说明
-D # #更改家目录指定
-MD # #更改家目录指定及家目录名称
-S # #更改shell
-L # #冻结帐号
-U # #解锁
-s/sbin/nologin User #指定交互式
What is the difference between 7:passwd-l user and usermod-l user?

Passwd-l User
Passwd-u User
Lock appears two!!
Usermod-l User
Usermod-u User
Lock appears one!
A: The former level is higher, the lock will appear two exclamation mark!! The latter only one!!
If you unlock with usermod-u user!! Need to enter two times command
8: Analysis of/etc/skel/catalogue?

Every time you create a new user (via the useradd command), the files in the/etc/skel directory will be copied to the new user's home directory intact.

Ls-a/etc/skel/
.  .. . bash_logout. Bash_profile. BASHRC game. Mozilla
The best choice is to put these settings in the global/etc/profile, the files in the Skel directory are copied in the past, if you modify or add new files, only the new users can benefit.

9. File/directory owner all Group Management # # # # #
Chown User File/directory (-R) (directory recursion) #更改目录或文件所有人
CHGRP user File/directory (-R) (directory recursion) #更改目录文件所有组
Chown user. User files/directories (-R) #同时更改所有人所有组

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User/user group summary in Linux