4-Linux group management and rights management

Basic introduction to the Linux group

In Linux, each user must belong to the same group and cannot be independent from the group.

In Linux, each file has the concepts of owner, group, and other groups.

• owner
  • Generally, it is the creator of the file, whoever creates the file will naturally become the owner of the file
• group
• other groups

The owner of the file/directory

• View file owner
  • ls -ahl
• change file owner
  • chown 用户名 文件名

group creation

• create group
  • groupadd 组名
• Create a user and put it in the monster group [[3-Linux practical operation#Add and delete user groups|Related operations of user groups]]
  • useradd -g monster fox

The group the file/directory belongs to

When a user creates a file, the group of the file is the group of the user.

• Check the group of the file/directory
  • ls -ahlYou can view the group where the file/directory is located by command
• Modify the group of the file/directory
  • chgrp 组名 文件名

other groups

In addition to the owner of the file and the users of the group, other users of the system are other groups of the file

Change the user's group

With root management authority, you can change the group of a user.

• Change the user's group
  • usermod -g 新组名 用户名
  • usermod -d 目录名 用户名 改变该用户登陆的初始目录
    • ❗️The user needs to have permission to enter the new directory

Basic introduction to permissions

Description of 0-9 digits

• Bit 0 : Determines the type of the file
  • lIt is a link, equivalent to a Windows shortcut
  • dIt is a directory, which is equivalent to a windows folder
  • cIt is a character device file, such as mouse, keyboard, etc.
  • bIs a block device, such as a hard disk
  • -It is an ordinary file, such as a *.txt file
• Bits 1-3 : Determine the file owner's permissions on the file – User
• Bits 4-6 : Make sure the group you belong to has permissions to the file – Group
• Bits 7-9 : Make sure other users (other groups) have permissions to the file – Other

Detailed explanation of rwx permissions

When rwx decorates the file

• [ r ]: stands for readable (read): the file can be read and viewed
• 【w】: Represents writable (write): can be modified, but it does not mean that the file can be deleted. The prerequisite for deleting a file is that the directory where the file is located has write permission to delete the file.
• [ x ]: stands for executable (execute): can be executed

When rwx modifies the directory

• [ r ]: stands for readable (read): the file can be read, ls to view the contents of the directory
• [ w ]: stands for writable (write): can be modified, create + delete or rename the contents of the directory
• [ x ]: stands for executable (execute): you can enter this directory

It can be represented by numbers: r=4, w=2, x=1 , so rwx=4+2+1=7.

other instructions:

Modify permissions

Basic instructions: Through chmodinstructions, you can modify the permissions of files or directories

The first way: +, -, = change permissions

The meaning of +, -, =:

• • Indicates increased permissions
• • Indicates the cancellation of permissions
• = Indicates the only setting permission

The meaning of u, g, o, a:

• u : owner
• g : all groups (in which group)
• o : others
• a : everyone

For example:

chmod u=rwx,g=rx,o=r 文件名/目录
chmod o+w 文件名/目录: Add write permission to other users
chmod a-x 文件名/目录: Remove execute permission from all users

The second way: changing permissions through numbers

r=4、w=2、x=1

chmod u=rwx,g=rw,o=r filename ==> chmod 751 filename

change file owner

chown newowner filename: change owner

chown newowner:newgroup filename: change owner and group

-R : If it is a directory, it should make all sub-files or directories under it recursively effective