Group Control
 

I have a file the owner is root:root ( mode is 644 ) , I want to release read & write permission to a non root user ( eg. admin_usr ) , I tried to create a specific group ( eg. ADM ) and release it to root user and admin_usr ( by adding this users to ADM in /etc/group ) , but it is not work , can advise if preserve the file mode to 644 , is it ok ? how to do it if I want to have read & write permission in my case ?

Hello,

Have a look at the following articles about ACL, I'm sure you'll be able to configure just what you need/want with them. The packages/commands discussed offer you possibilities beyond the standard ones on file permissions.

Linux File Security
Know your rights

Kind regards,

Eric

So are you wanting only root to have access to the file? If you just want the owner root to have access, you could make the permissions 600.

Maybe I am misunderstanding what you want to do.

To enable the orig soln, you'd have to change the group owner of the file to the new grp ADM:

change the group ownership

chgrp ADM file1name


gpasswd -M admin_usr ADM

What I think this means is that currently only root can read/write but you want another user (who is a member of admin_usr) to be able to?

In which case the above (chgrp) will still retain the existing permissions on the file (ie, 644). You will need to:
so that the group has rw.