CentOSchmod command usage

Command name: chmod permission: Usage of all users: chmod [-cfvR] [-- help] [-- version] modefile... 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. Parameter: mode: permission setting string. format: [ugoa...] [[+-=] [rwxX].

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.