1. Linux user (account) management
Query user (account) information (judging whether the user (account) exists)
id account
Add new user (account)
useradd account
Set user (account) password
方式1：
passwd account
方式2：
echo 123|passwd --stdin account; #密码为123
Delete user (account)
删除用户(账号)只能root登陆进行删除
方式1：保留用户(账号)目录。
userdel account
方式2：不保留用户(账号)目录。（不建议）
userdel -r account
Query the currently logged in user (account) information
who am i
Switch user (account)
su - account
2. User (account) group
An intermediate role created to facilitate the management of user (account) permissions. A
user (account) added to a user group has all the permissions of the group
and does not override the user (account)'s own unique permissions.
new group
groupadd wudang
delete group
groupdel wudang
Specify user groups when creating users
useradd -g 用户组 用户名
useradd -g wudang zwj
#创建一个账号zwj，指定分组为wudang，
#如果创建账号不指定分组，系统会默认用账号创建一个分组，并把该账号归档到该用户组。
modify user group
usermod -g 用户组 用户名
usermod -g shaolin zwj #把用户zwj重新分组到shaolin组里
3. Important files of users and groups
/etc/passwd 记录了所有用户
/etc/shadow 记录了账号密码
/etc/group 记录了所有用户组
4. Summary
Our usual ideas for creating users should be as follows:
1. Check whether the user group has been created.
cat /etc/group |grep wudang
2. Create user groups.
groupadd wudang
3. Create users and specify user groups.
useradd -g wudang zwj;
4. Set a password for the user account.
echo 123|passwd --stdin zwj;
5. Assign corresponding permissions to user groups.
[root@localhost ~]# chmod [ugoa] [=+-] [rwx] 文件或目录...
u 属主 g 属组 o 其他用户 a 所有
= 赋予...权限 + 加上...权限 - 去掉...权限
-R //递归修改指定目录下所有文件、子目录的权限
