Linux File/directory permissions

File type permission belongs to the main group directory name/file name
DRWX------2 Alice girls 4096 September 11:33 Alice
DRWX------2 Rose girls 4096 September 10:47 Rose
DRWX------2 Tom boys 4096 September 10:43 Tom

File type:-Normal file D directory

O (∩_∩) o~~ File/directory permissions:
1. User owner (creator U of main owner file)
2. Group G where Group owner is located
For example: Useradd-g girls Alice Alice belongs to the girls group
Useradd xiaohong default Xiaohong group name is Xiaohong
Alice and Rose are in the girls group.
3. Other o is neither user nor in the same group

Ls-l starts with 10 characters:
File type file/directory permissions
-File---------
D Directory owner Group Other

4. Three kinds of access rights: readable R, writable W, executable x
RWX------appear fixed rwx missing use-replace
R Readable r--100 4
W Writable-w-010 2
X executable--x 001 1

-rw-r--r--Normal file: 644 permissions of the digital expression method concise
Self: readable, writable same group: read-only other: read-only

D rwx r-x r-x directory: Permissions 755
Self: readable, writable, executable
Same group: readable, executable other: readable, executable

-rwx rwx rwx executable file 777
For all users: readable, writable, executable

The method of digital expression of right permission
421
0---
001 1--x
010 2-w-
011 3-WX
4 r--
101 5 R-x
6 rw-
111 7 rwx

5, summarize the file and directory of the various rules of authority:
1) file permissions: R readable can use VI, cat to view the contents of the file
W writable can be modified after saving
x executable can be run directly command is executable file

2) directory permissions: R readable LS directory, can see content
W writable can modify directory contents, such as new, delete directory
x executable can be CD in

6. Command to modify file/directory permissions: chmod
Role: U owner user
G Same group
o Other
A All of
Usage:
# chmod u+x 1.txt Add executable permissions for yourself
# chmod u-x 1.txt Remove executable permissions for yourself
# chmod g+w 1.txt Add writable permissions for the same group
# chmod a+r,g+w 1.txt All users are readable, the same group of writable
# chmod 777 1.txt Digital Expression method
RWX rwx rwx
# chmod 644 1.txt

Premise: Only the file owner, root user can change permissions

Case: Modify Alice Home directory permissions by root or Alice:
For O + Rx, other user xiaohong can enter the Alice home directory and can use Ls-l to view current content.
O+w Xiaohong can modify the file by root or Alice to modify the permissions for the 1.txt file. 644-646
rw-r--r--rw-r--rw-
chmod 646 1.txt

Linux File/directory permissions