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.