Detailed usage of the CHMOD command

Command name: chmod
Permission: All Users
Usage: chmod [-CFVR] [-- help] [-- version] mode file...
Note: The file calling permissions for Linux/Unix are divided into three levels: file owner, group, and others. Chmod can be used to control how files are called by others.
Parameters:
Mode: permission setting string in the following format: [ugoa...] [[+-=] [rwxx]...] [,...], where
U indicates the owner of the file, G indicates that the owner of the file belongs to the same group, O indicates that the owner of the file belongs to other people, and a indicates that all three are.
+ Adds a permission,-Indicates canceling the permission, and = indicates a unique permission.
R indicates that the file can be read, W indicates that the file can be written, and X indicates that the file can be executed only when the file is a subdirectory or the file has been set to executable.
-C: if the permission of the file has been changed, the change action is displayed.
-F: Do not display an error message if the file permission cannot be changed.
-V: displays details of permission changes.
-R: Change the permissions of all files and sub-directories in the current directory in the same way (that is, change one by one in the way of delivery)
-- Help: displays auxiliary instructions
-- Version: displays the version.
Example: Set the file file1.txt to readable by all users:
Chmod Ugo + R file1.txt
Set file1.txt to readable:
Chmod A + R file1.txt
Set file1.txt and file2.txt as the owner of the archive, which can be written to the same group to which the archive belongs, but not to others:
Chmod ug + W, o-w file1.txt file2.txt
Set ex1.py to only the owner of the file to execute:
Chmod U + x ex1.py
Set all files and subdirectories in the current directory to be readable by anyone:
Chmod-r a + R *
In addition, chmod can use numbers to indicate permissions, such as chmod 777 file.
Syntax: chmod ABC File
Each A, B, and C is a number, indicating the permissions of the user, group, and other respectively.
R = 4, W = 2, x = 1
If you want the rwx attribute, 4 + 2 + 1 = 7;
If the RW-attribute is required, 4 + 2 = 6;
If you want the R-x attribute, 4 + 1 = 7.
Example:
Chmod A = rwx File
And
Chmod 777 File
Same effect
Chmod ug = rwx, O = X file
And
Chmod 771 File
Same effect
If chmod 4755 filename is used, the program can have root permissions.