How to use the Linux chmod command

Linux/Unix file calling permissions are divided into three levels: file owner, group, and others. Chmod can be used to control how files are called by others.

Permission: all users

Syntax

Chmod [-cfvR] [-- help] [-- version] mode file...

Parameter description

• 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 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: If the file permission cannot be changed, do not display an error message.

• -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.

Instance

Set file1.txt to readable by all users:

Chmod ugo + r file1.txt

Set file1.txt to readable by all users:

Chmod a + r file1.txt

Set file1.txt and file2.txt as the owner of the file, which can be written to the same group, but not to others:

Chmod ug + w, o-w file1.txt file2.txt

Set ex1.py to be executed only by the file owner:

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 also use numbers to indicate permissions, for example:

Chmod777file

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 = 5.

Chmod a = rwx file

And

Chmod777file

Same effect

Chmod ug = rwx, o = x file

And

Chmod771file

Same effect

If chmod 4755 filename is used, the program can have root permissions.