This Gist contains basics Linux File & Folder Permission Management Commands and their meaning, this gist's sole purpose is to help students learn basic file management commands.

Linux Series part 2: File & Folder Permission Management.txt

Linux Series part 2: File & Folder Permission Management:

To see file list, their crrent permission level and much more, you can run:
ls -la -lh -lt  
(To know more on ls commands check tutorial: https://www.youtube.com/watch?v=h6sDtGN5hYs)

chmod <specification> filename : Change the file permissions. Specifications = u user/owner, g group, o other, + add permission, - remove, r read, w write,x execute.

chmod -R <specification> dir-name: Change the permissions of a directory recursively. To change permission of a directory and everything within that directory, use this command.

chmod go=+r myfile - Add read permission for the owner and the group 

chmod a+rwx myfile Allow all users to read, write or execute myfile.

chmod go-r myfile - Remove read permission from the group and others. 


You Can do it in Numerical way as well:

chmod 777 sample_file.txt
Where it means: Everybody can read, write to, or execute sample_file.txt
Each digit of this code sets permissions for one of these groups as follows. Read is 4. Write is 2. Execute is 1.
The sums of these numbers give combinations of these permissions:

0 = no permissions whatsoever; this person cannot read, write, or execute the file
1 = execute only
2 = write only
3 = write and execute (1+2)
4 = read only
5 = read and execute (4+1)
6 = read and write (4+2)
7 = read and write and execute (4+2+1)

Sample combination:
Command	            Meaning
chmod 700 sample_file.txt	Only you can read, write to, or execute sample_file.txt
chmod 777 sample_file.txt	Everybody can read, write to, or execute sample_file.txt
chmod 744 sample_file.txt	Only you can read, write to, or execute sample_file.txt Everybody can read sample_file.txt;
chmod 444 sample_file.txt	You can only read sample_file.txt, as everyone else.

let's break it into more simple words:
e.g. we have a test file as test.txt and we want write access to owner of file only, so now:
Owner rwx = 4+2+1 = 7
Group r-x = 4+0+1 = 5
Other r-x = 4+0+1 = 5
So the entire command will be:
chmod 755 test

Other uses & Commands:

chmod owner1 filename - Change ownership of a file to user owner1. 

chgrp grp_owner filename - Change primary group ownership of file filename to group grp_owner. 

chgrp -R grp_owner dir-name - Change primary group ownership of directory dir-name to group grp_owner recursively. To change group ownership of a directory and everything within that directory, use this command.


Note: If you want to try above commands without any risk, use Docker, so install docker and use below docker commands to run a Linux cotainer and use the shell, e.g. as in tutorial I have shown:
docker run -it ubuntu:16.04 /bin/bash 
But you can use any linux OS , it's your choice. Docker Tutorial Link: https://www.youtube.com/watch?v=Y56FMHC1mb8