Linux chmod command parsing and linuxchmod Parsing

Linux chmod command parsing and linuxchmod Parsing

Chmod command

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:

Chmod ugo + r file.txt set the file file.txt to be readable by all users.

Chmod a + r file.txt sets the file file.txt to be readable by all users.

Chmod ug + w, o-w file.txt set file.txt and file.txt as the owner of the archive, which can be written to the same group but not to others.

Chmod u + x ex1.py sets ex1.py to be executed only by the owner of the file.

Chmod-R a + r * sets all files and subdirectories in the current directory as readable by anyone.

Use numbers to indicate Permissions

Syntax: chmod abc file

Parameter: 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 you want the rw-attribute, 4 + 2 = 6.

If you want the r-x attribute, 4 + 1 = 7.

Example:

Chmod a = rwx file and chmod 777 file have the same effect.

Chmod ug = rwx, o = x file, and chmod 771 file have the same effect.

If you use chmod 4755 filename, this program can have root permissions.