[ubuntu] allow two users to read/write files and folders to an specific folder

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http://ubuntuforums.org – hi, I want to allow two users to read/write privileges to an specific files and folders, currently the owner of the dir is "user1.user1", so, I add the user "user2" the "user1 group" with this command: Code: nano /etc/group then i tried that the user2 to write files into that directory but it does not work, the error got it was: "permission denied", so my question is: what command should i use to add permission to user1 and user 2 to read/write files? regards (Hardware)